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 HERMES PUBLICATIONS 
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Last update: Dec 7, 2020

Dec 7, 2020
Azimuthal single- and double-spin asymmetries in semi-inclusive deep-inelastic lepton scattering by transversely polarized protons
A. Airapetian et al, JHEP (in press) *PDF
Eprint numbers: arXiv:2007.07755 and DESY-20-119
SUBJECT: TRANSVERSE
CITATIONS: SPIRES at SLAC, DESY

Sep 25, 2019
Beam-helicity asymmetries for single-hadron production in semi-inclusive deep-inelastic scattering from unpolarized hydrogen and deuterium targets
A. Airapetian et al, Phys. Lett. B 797 (2019) 134886 *PDF
Eprint numbers: arXiv:1903.08544 and DESY-19-040
INFO: DOI: 10.1016/j.physletb.2019.134886
SUBJECT: AZIMUTHAL: beam
CITATIONS: SPIRES at SLAC, DESY

Apr 15, 2019
Longitudinal double-spin asymmetries in semi-inclusive deep-inelastic scattering of electrons and positrons by protons and deuterons
A. Airapetian et al, submitted to Phys. Rev. D *PDF
Eprint numbers: arXiv:1810.07054 and DESY-18-181
SUBJECT: DELTA-Q
CITATIONS: SPIRES at SLAC, DESY

Jun 13, 2017
Ratios of helicity amplitudes for exclusive rho⁰ electroproduction on transversely polarized protons
A. Airapetian et al, Eur. Phys. J. C 77 (2017) 378 *PDF
Eprint numbers: arXiv:1702.00345 and DESY-17-017
INFO: DOI 10.1140/epjc/s10052-017-4899-1
SUBJECT: EXCLUSIVE: rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Definition of angles in the process eN -> e\rho^{0}N->e\pi^{+}\pi^{-}N. Here, \PHI is the angle between the \rho^{0} production plane and the lepton scattering plane in the CM system of virtual photon and target nucleon. The variables \theta and \phi are respectively the polar and azimuthal angles of the decay \pi^{+} in the \rho^{0}-meson rest frame, with the z axis being anti-parallel to the outgoing nucleon momentum. The XZ and xz planes both the \gamma^{\star} and \rho^{0} three-momenta
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Figure 2 : Helicity-amplitude ratios obtained from the 25-parameter fit characterized by = 4.73 GeV, = 1.93 GeV^{2}, <-t^{\prime}> = 0.132 GeV^{2}
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Figure 3 : Comparison of the SDMEs u^{\lambda_{V}\lambda_{V^{\prime}}_{\lambda_{\gamma}\lambda_{\gamma^{\prime}}} obtained from the amplitude method (red circles) and from the SDME method (blue triangles). The SDMEs are extracted in the entire kinematic region. The points in the shaded area show SDMEs that can be obtained only if the beam is longitudinally polarized
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Figure 4 : Comparison of the SDMEs n^{\lambda_{V}\lambda_{V^{\prime}}_{\lambda_{\gamma}\lambda_{\gamma^{\prime}}} obtained from the amplitude method (red circles) and from the SDME method (blue squares). The SDMEs are extracted in the entire kinematic region. The points in the shaded area show SDMEs that can be obtained only if the beam is longitudinally polarized in addition to the transverse target polarization required for all SDMEs here
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Figure 5 : Comparison of the SDMEs s^{\lambda_{V}\lambda_{V^{\prime}}_{\lambda_{\gamma}\lambda_{\gamma^{\prime}}} obtained from the amplitude method (red circles) and from the SDME method (blue squares). The SDMEs are extracted in the entire kinematic region. The points in the shaded area show SDMEs that can be obtained only if the beam is longitudinally polarized in addition to the transverse target polarization required for all SDMEs here
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Figure 6 : Comparison of amplitude ratios to those calculated in the Goloskokov-Kroll model
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May 10, 2016
Spin density matrix elements in exclusive omega electroproduction on ¹H and ²H targets at 27.6 GeV beam energy
A. Airapetian et al, Eur. Phys. J. C 74 (2014) 3110 *PDF
Eprint numbers: arXiv:1407.2119 and DESY-14-116
INFO: DOI 10.1140/epjc/s10052-014-3110-1 This is the arXiv version, which includes the corrected figure 6 [see Erratum Eur. Phys. J C 76 (2016) 162; DOI 10.1140/epjc/s10052-016-3996-x]
SUBJECT: VECTOR-MESONS: omega spin density matrix elements
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Definition of angles in the process eN \rightarrow eN\omega, where \omega \rightarrow \pi^{+}\pi^{-}\pi^{0}
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Figure 2 : Two photon invariant mass distribution after application of all criteria to select exclusively produced \omega mesons. The Breit-Wigner fit to the mass distribution is shown as a continuous line and the dashed line indicates the PDG value of the \pi^{0} mass
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Figure 3 : Breit-Wigner fit (solid line) of \pi^{+}\pi^{-}\pi^{0} invariant mass deistribution after application of all criteria to select \omega mesons produced exclusively from proton (top) and from deuteron (bottom). The dashed line represents the PDG value of the \omega mass
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Figure 4a : The \Delta E distribution of \omega mesons produced in the entire kinematic region is compared with SIDIS \Delta E distributions from PYTHIA (shaded area). The vertical dashed line denotes the upper limit of the exclusive region
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Figure 4b : The \Delta E distribution of \omega mesons produced in the first -t^{\prime} kinematic bins is compared with SIDIS \Delta E distributions from PYTHIA (shaded area). The vertical dashed line denotes the upper limit of the exclusive region
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Figure 4c : The \Delta E distribution of \omega mesons produced in the second -t^{\prime} kinematic bins is compared with SIDIS \Delta E distributions from PYTHIA (shaded area). The vertical dashed line denotes the upper limit of the exclusive region
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Figure 4d : The \Delta E distribution of \omega mesons produced in the third -t^{\prime} kinematic bins is compared with SIDIS \Delta E distributions from PYTHIA (shaded area). The vertical dashed line denotes the upper limit of the exclusive region
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Figure 5a : Distributions of several kinematic variables from experimental data on exclusive \omega meson leptoproduction (black squares) in comparison with simulated exclusive events from the PYTHIA generator (dashed areas). Simulated events are normalized to the experimental data
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Figure 5b : Distributions of several kinematic variables from experimental data on exclusive \omega meson leptoproduction (black squares) in comparison with simulated exclusive events from the PYTHIA generator (dashed areas). Simulated events are normalized to the experimental data
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Figure 6 : The 23 SDMEs for exclusive \omega electroproduction extracted in the entire HERMES kinematic region with \left\langle Q^{2} \right\rangle = 2.42 GeV^{2}, \left\langle W \right\rangle = 4.8 GeV, \left\langle -t^{\prime} \right\rangle = 0.080 GeV^{2}. Proton data are denoted by squares and deuteron data by circles. The inner error bars represent the statistical uncertainties, while the outer ones indicate the statistical and systematic uncertainties added in quadrature. Unpolarized (polarized) SDMEs are displayed in the unshaded (shaded) areas
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Figure 7 : Q^{2} and -t^{\prime} dependences of class-A SDMEs. Proton data are denoted by squares and deuteron data by circles. Data points for deuteron are slightly shifted horizontally for legibility
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Figure 8 : Q^{2} and -t^{\prime} dependences of class-B SDMEs
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Figure 9a : Q^{2} dependence of class-C SDMEs
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Figure 9b : -t^{\prime} dependence of class-C SDMEs
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Figure 10a : Q^{2} dependence of class-D SDMEs
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Figure 10b : -t^{\prime} dependence of class-D SDMEs
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Figure 11 : Q^{2} and -t^{\prime} dependences of class-E SDMEs
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Figure 12 : Comparison of SDMEs in exclusive \omega and \rho^{0} electroproduction at HERMES for the entire kinematic region. The average values of the kinematic variables in exclusive \rho^{0} production are \left\langle Q^{2} \right\rangle = 1.95 GeV^{2}, \left\langle W \right\rangle = 4.8 GeV, and \left\langle -t^{\prime} \right\rangle = 0.13 GeV^{2}
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Figure 13 : The Q^{2} and -t^{\prime} dependences of u_{1},u_{2} and u_{3}. The open symbols represent the values over the entire kinematic region
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Figure 14 : The Q^{2} (left) and -t^{\prime} (right) dependences of the longitudinal-to-transverse virtual photon differential cross-section ratio for exclusive \omega and \rho^{0} electroproduction at HERMES, where the -t^{\prime} bin covers the interval [0.0-0.2] GeV^{2} for \omega production and [0.0-0.4] GeV^{2} for \rho^{0} production. The symbols that are parenthesized in the legend represent the value of R in the entire kinematic region
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Figure 15 : The Q^{2} and -t^{\prime} dependences of the UPE-to-NPE asymmetry P of the transverse differential cross-section for exclusive \omega electroproduction at HERMES. The open symbols represent the values over the entire kinematic region
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Mar 14, 2016
Reply to “Comment on ‘Reevaluation of the parton distribution of strange quarks in the nucleon'”
E.C. Aschenauer et al, Phys. Rev. D 92 (2015) 098102 *PDF
Eprint numbers: arXiv:1508.04020
INFO: Reply to Comment by M. Stolarski [published in PRD 92, 098101 (2015)]. Not a regular HERMES publication, but on behalf of HERMES.
SUBJECT: UNPOL-PDF: sea-flavour
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Comparison of the shapes of multiplicities corrected to 4\pi of charged kaons and pions in semi-inclusive DIS from a deuterium target, as a function of Bjorken x_B. The kaon multiplicities are scaled to agree with those of pions in the range of xB where both distributions flatten. Data are plotted at the average x_B of each individual x_B bin
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Figure 2 : Born space in (x_B, Q²) corresponding to the multiplicities reported in Ref. [2]. Kinematic regions covered by two data points with similar average kinematics, as discussed in the Comment [3], are superimposed (highlighted slices in either x_B or Q²). Note that the color coding is logarithmic, and that most of the events [O(70%)] in either of the two bins are in fact not shared
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Figure 3a : K^{\prime} "multiplicities" corrected to 4\pi of charged kaons in semi-inclusive DIS from a deuterium target, as a function of x_B, evaluated with Eq. (4) using MSTW08 (squares), CTEQ6 (upward triangles), NNPDF3.0 (downward triangles), and NNPDF2.3 (full circles) LO PDF sets. Also shown are the LO predictions [e.g., Eq. (5)] using DSS FFs (crosses) or using the high-x_B HERMES data to constrain the unfavored \bar{u} and \bar{d} to K^{+} FFs (stars). For both the crosses and stars, S\int{dzD_S^K} from Ref. [1] and Q from NNPDF3.0 were used. Note that uncertainties on PDFs or FFs-when available at all-were not propagated, but only total experimental uncertainties
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Figure 3b : K^{\prime} "multiplicities". Equation (5) evaluated in the same way as the crosses to the left, but for a range of scaled DSS unfavored nonstrange kaon FFs [using scaling factors from 0 (bottom) to 4 (top) as in Fig. 2 (left) in the Comment]. As in the Comment [3], all points were evaluated at the average Q² of each individual x_B bin
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Figure 4 : The Q² dependence of the DSS favored u and \bar{s} (scaled by a factor 1/7) as well as the unfavored \bar{u} to K^{+} fragmentation functions. Note that for the DSS FF set D^{K⁺}_\bar{u} = D^{K⁺}_\bar{d} . Chosen Q² values correspond to the average Q² of the x_B bins in Figs. 3(ab) and 5
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Figure 5 : The scaled charge-difference multiplicities dN^K^{diff}/ dN^{DIS}. (⁵Q + ²S)/[4(uv + dv)] of charged kaons in semi-inclusive DIS from a deuterium target, as a function of x_B, evaluated using various LO PDF sets [MSTW08 (squares), CTEQ6 (upward triangles), NNPDF3.0 (downward triangles), and NNPDF2.3 (circles)], compared with the LO predictions based on solely DSS FFs (crosses) and DSS FFs combined with unfavored kaon FFs constrained using HERMES data at high x_B (stars). As in the Comment [3], all points were evaluated at the average Q² of each individual x_B bin
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Jan 15, 2016
Transverse-target-spin asymmetry in exclusive omega-meson electroproduction
A. Airapetian et al, Eur. Phys. J. C 75 (2015) 600 *PDF
Eprint numbers: arXiv:1508.07612 and DESY-15-149
INFO: DOI 10.1140/epjc/s10052-015-3825-7
SUBJECT: VECTOR-MESONS: asymmetry, omega
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Two-photon invariant-mass distribution after application of all criteria to select exclusively produced omega mesons. The Breit-Wigner fit to the mass distribution is shown as a continuous line and the vertical dashed line indicates the PDG value of the \pi^{0} mass
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Figure 2 : Missing-energy distribution for exclusive omega meson production. The unshaded histogram shows experimental data, while the shaded area shows the distribution obtained from a PYTHIA simulation of the SIDIS background. The vertical dashed line denotes the upper limit of the exclusive region
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Figure 3 : The \pi^{+}\pi^{-}\pi^{0} invariant-mass distribution after application of all criteria to select exclusively produced omega mesons. The Breit-Wigner fit to the mass distribution is shown as a continuous line and the vertical dashed line indicates the PDG value of the omega mass
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Figure 4 : Lepton-scattering and omega production planes together with the azimuthal angles \phi and \phi_{S}
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Figure 5 : The five amplitudes describing the strength of the sine modulations of the cross section for hard exclusive omega meson production. The full circles show the data in two bins of Q^{2} or -t^{\prime}. The open squares represent the results obtained for the entire kinematic region. The inner error bars represent the statistical uncertainties, while the outer ones indicate the statistical and systematic uncertainties added in quadrature. The results receive an additional 8.2% scale uncertainty corresponding to the target-polarization uncertainty. The solid (dash-dotted) lines show the calculation of the GK model for a positive (negative) \pi\omega transition form factor, and the dashed lines are the model results without the pion pole
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Figure 6 : As Fig. 5, but only for transversely polarized omega mesons
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Nov 25, 2015
Bose-Einstein correlations in hadron-pairs from lepto-production on nuclei ranging from hydrogen to xenon
A. Airapetian et al, Eur. Phys. J. C 75 (2015) 361 *PDF
Eprint numbers: arXiv:1505.03102 and DESY-15-074
INFO: DOI: 10.1140/epjc/s10052-015-3566-7
SUBJECT: BEC
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Schematic illustration of the Bose–Einstein effect
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Figure 2 : Top panel: normalized experimental (stars) and simulated (line) distributions for unlike-sign hadron pairs as a function of the variable T. Bottom panel: the ratio of these experimental (exp) and simulated (MC) distributions
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Figure 3 : Consistency check of the two chosen reference samples. The quantity R^TST is defined in the text. The curve is a linear fit to the data for T between 0.05 GeV and 1.3 GeV
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Figure 4 : Double ratio correlation function for like-sign hadron pairs obtained with MEM and MUS based on hydrogen target data
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Figure 5 : Parameter r_G (top panel) and λ (bottom panel) as a function of W, obtained with MEM and MUS methods on hydrogen. The inner and outer error bars indicate the statistical and total uncertainties. For the latter the statistical and systematic uncertainties are added in quadrature
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Figure 6 : Goldhaber radius r_G, as a function of W, obtained in lepton nucleon scattering experiments. Different markers are used to indicate the different methods for the construction of the reference sample and the kinds of uncertainties included
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Figure 7 : The parameters r_G (top panel) and λ (bottom panel) are shown as a function of the target atomic mass A. The inner part of the error bars indicate the statistical uncertainty and the total error bars have systematic uncertainties added in quadrature. The horizontal lines correspond to the average value of the parameters
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Apr 13, 2015
Pentaquark Theta+ search at HERMES
N. Akopov et al, Phys. Rev. D 91 (2015) 057101 *PDF
Eprint numbers: arXiv:1412.7317 and DESY-14-245
INFO: DOI: 10.1103/PhysRevD.91.057101
SUBJECT: EXOTICS: pentaquark
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Diagram of the kinematic reconstruction of the decay of a \Theta^{+}. The angle \alpha is the difference in the direction of the K_{S}^{0} momentum (dotted line), as given by the pion momenta, and by the vector connecting the event origin, V_{p}^{Beam}, with the decay of the K_{S}^{0} (dash-dotted line)
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Figure 2 : Invariant-mass spectra of two oppositely charged pions showing a clear K_{S}^{0} signal peak. The black squares denote this analysis with data from 1998-2000 and 2006-2007 while the open circles are the previously published analysis of the 1998-2000 data For comparison, the standard deviations and mean values of a single Gaussian function fit to the data together with a third-order Chebychev function for the background are given. The new analysis has a much improved mass resolution and signal-to-noise ratio compared to that of the previous HERMES analysis
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Figure 3 : The various M(pK_{S}^{0}) spectra for deuterium data taken at the HERMES experiment in the years 1998-2000 (top), 2006-2007 (middle), and for both periods combined (bottom). Also shown in the top panel is the previously published spectrum from 1998-2000 of data that has been reanalyzed here. A Voigtian (using a Gaussian with a width fixed to 6 MeV) together with two different background hypotheses was fitted to the summed spectrum in the bottom panel. The resulting curves are shown separated into signal and background contribution and also combined. The width \Gamma of the Breit-Wigner function, the peak position M, and the number of signal events obtained from the fits are given in the panel
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Figure 3a : M(pK_{S}^{0}) spectrum for combined deuterium data taken at the HERMES experiment in the years 1998-2000 and 2006-2007
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Figure 4 : M(pK_{S}^{0}) spectrum from the hydrogen target
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Oct 20, 2014
Transverse polarization of Lambda hyperons from quasireal photoproduction on nuclei
A. Airapetian et al, Phys. Rev. D 90 (2014) 072007 *PDF
Eprint numbers: arXiv:1406.3236 and DESY-14-097
INFO: DOI: 10.1103/PhysRevD.90.072007
SUBJECT: LAMBDA-POL: transverse
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Invariant-mass distributions for \Lambda events obtained with hydrogen and deuterium targets (top panel) and with krypton and xenon targets (bottom panel). The vertical lines indicate the invariant-mass interval used for the determination of the \Lambda polarization. The quantities given in the legends are the number of analyzed \Lambda events, N^{\Lambda}, in the selected invariant-mass window after subtraction of background events, the reconstructed \Lambda mass M^{\Lambda}, the resolution \sigma of the invariant-mass distribution, and the fraction \eta of \Lambda events in this mass window
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Figure 2 : Sketch of \Lambda production and decay. The polarization vector \vec{P^{\Lambda}_{n}} is directed along the normal \hat{n} to the \Lambda production plane; \theta is the angle between the momentum of the decay proton and \hat{n} in the rest frame of the \Lambda hyperon
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Figure 3 : Dependence of the transverse polarization P^{\Lambda}_{n} on the atomic-mass number A of the target nuclei. The inner error bars represent the statistical uncertainties; the full error bars represent the total uncertainties, evaluated as the sum in quadrature of statistical and systematic uncertainties
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Figure 4 : Dependence of the transverse polarization P^{\Lambda}_{n} for the combined hydrogen and deuterium data (closed symbols) and the combined krypton and xenon data (open symbols) on the variable \zeta. The error bars represent statistical uncertainties only; the systematic uncertainties are not shown, since they are strongly correlated for the kinematic dependences. The values of \left\langle p_{T} \right\rangle for each \zeta bin are shown in the lower panel
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Figure 5 : Dependence of the transverse polarization P^{\Lambda}_{n} on the transverse \Lambda momentum p_{T}. Closed circles (squares) represent the combined hydrogen and deuterium data for the region \zeta < 0.2 (\zeta > 0.3). The combined krypton and xenon data (open triangles) are shown for the full \zeta range. The error bars represent the statistical uncertainty. The values of \left\langle \zeta \right\rangle for each p_{T} bin are shown in the lower panel
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Jun 14, 2014
Reevaluation of the parton distribution of strange quarks in the nucleon
A. Airapetian et al, Phys. Rev. D 89 (2014) 097101 *PDF
Eprint numbers: arXiv:1312.7028 and DESY-13-246
INFO: DOI: 10.1103/PhysRevD.89.097101
Summary of paper for the general science reader: *PDF
SUBJECT: UNPOL-PDF: sea-flavour
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The multiplicity of charged kaons in semi-inclusive DIS from a deuterium target, as a function of Bjorken x. The continuous curve is calculated from the strange-quark contribution taken from the fit in Fig. 3, together with the non-strange contribution as extracted from the high-x multiplicity data (see text). The green dashed (magenta dash-dotted) curve shows separately the nonstrange- (strange-) quark contribution to the multiplicity for that fit. The blue-dotted curve is the LO prediction obtained with CTEQ6L PDFs and fragmentation functions from [9]. The values of the average Q² for each x bin are shown in the lower panel. The band represents systematic uncertainties
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Figure 2 : The strange-parton distribution xS(x,Q²) from the measured HERMES multiplicity for charged kaons evolved to Q² = 2.5 GeV² using the compilation of fragmentation functions (FFs) from [9] (DSS). The solid curve is a three-parameter fit to the data, the dashed curve gives xS(x) from CTEQ6L, and the dot-dash curve is the sum of light anti-quarks from CTEQ6L. The dotted curve is from CTEQ 6.5 S-0, a PDF reference set [10] in which the shape of xS(x) has not been constrained. The band containing the experimental points represents the fully correlated systematic uncertainties arising from the imprecision of \int D_Q^K (z, Q²)dz
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Figure 3 : The product, S(x,Q²)\int D_S^K (z, Q²)dz, of the strange-quark PDF and the integral of the fragmentation function for strange quarks (squares) obtained from the measured HERMES multiplicity for charged kaons at the average Q² for each bin. The solid curve is a least-squares fit with the result f(x)=x^{-0.834\pm0.019} e^{-x/(0.0337\pm0.0014)} (1-x). The band represents propagated experimental systematic uncertainties. The open points and the dashed curve show the data and fit published previously in Ref. [7]
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Figure 4 : The strange-parton distribution xS (x, Q² ) from the measured HERMES multiplicity for charged kaons evolved to Q² = 2.5 GeV² assuming \int D_S^K (z, Q²)dz = 1.27. The solid curve is a two-parameter fit with S(x)=(\int D_S^K (z, Q²)dz)^-1 x^{-0.867\pm0.019} e^{-x/(0.0331\pm0.0014)} (1-x). The dashed, dot-dash, dotted curves are as given in Fig. 2. The broad band is the \pm 1 sigma zone of allowed values predicted by the neural network (NNPDF2.3) reference set [14]. The band at the bottom represents the propagated experimental systematic uncertainties. A scale uncertainty of approximately 10% coming from the precision of \int D_S^K (z, Q²)dz is not shown
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Jan 20, 2014
Beam-helicity asymmetry in associated electroproduction of real photons ep → eγπN in the ∆-resonance region
A. Airapetian et al, JHEP01(2014)077 *PDF
Eprint numbers: arXiv:1310.5081 and DESY-13-188
INFO: DOI: 10.1007/JHEP01(2014)077 ISSN: 1029-8479
SUBJECT: DVCS: associated
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : Distribution of chi²(ep->e\gamma\pi0p) for the channel ep->e\gamma\pi0p. Experimental data are presented by points, and the results of the Monte Carlo simulation by lines. Contributions from the associated, ep-> e\gammap, and SIDIS reactions are shown by red dash-dotted, blue dashed, and green dotted lines, respectively. Data and Monte Carlo yields are normalized to the corresponding numbers of DIS events
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Figure 1b : Distribution of chi²(ep->e\gamma\pi+n) for the channel ep->e\gamma\pi+n. Experimental data are presented by points, and the results of the Monte Carlo simulation by lines. Contributions from the associated, ep-> e\gammap, and SIDIS reactions are shown by red dash-dotted, blue dashed, and green dotted lines, respectively. Data and Monte Carlo yields are normalized to the corresponding numbers of DIS events
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Figure 2a : Distributions of t for the associated channel ep->e\gammapi0p. Notations are the same as in figure 1
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Figure 2b : Distributions of xB for the associated channel ep->e\gammapi0p. Notations are the same as in figure 1
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Figure 2c : Distributions of Q² for the associated channel ep->e\gammapi0p. Notations are the same as in figure 1
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Figure 2d : Distributions of t for the associated channel ep->e\gammapi+n. Notations are the same as in figure 1
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Figure 2e : Distributions of xB for the associated channel ep->e\gammapi+n. Notations are the same as in figure 1
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Figure 2f : Distributions of Q² for the associated channel ep->e\gammapi+n. Notations are the same as in figure 1
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Figure 3 : Amplitudes of the single-charge beam-helicity asymmetry extracted in the associated channel ep->e\gammapi0p obtained with recoil-proton reconstruction. The amplitudes are presented in projections of -t, xB, and Q². The "overall" results shown in the very left panel are extracted in a single kinematic bin covering the entire kinematic acceptance. Statistical (systematic) uncertainties are represented by error bars (bands). A separate scale uncertainty arising from the measurement of the beam polarization amounts to 1.96%
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Figure 4 : Amplitudes of the single-charge beam-helicity asymmetry extracted in the associated channel ep->e\gammapi+n obtained with recoil-proton reconstruction. The amplitudes are presented in projections of -t, xB, and Q². The "overall" results shown in the very left panel are extracted in a single kinematic bin covering the entire kinematic acceptance. Statistical (systematic) uncertainties are represented by error bars (bands). A separate scale uncertainty arising from the measurement of the beam polarization amounts to 1.96%
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Dec 9, 2013
Transverse target single-spin asymmetry in inclusive electroproduction of charged pions and kaons
A. Airapetian et al, Phys. Lett. B 728 (2014) 183-190 *PDF
Eprint numbers: arXiv:1310.5070 and DESY-13-187
INFO: DOI: 10.1016/j.physletb.2013.11.021
SUBJECT: TRANSVERSE: inclusive
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The definition of the azimuthal angle $\psi$
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Figure 2a : A^{sin\psi}_{UT} amplitudes for charged pions and kaons as a function of P_{T}. Positive (negative) particles are denoted by closed (open) symbols. When visible, the inner error bars show the statistical uncertainties, while the total ones represent the quadratic sum of statistical and systematic uncertainties. Not shown is an additional 8.8% scale uncertainty due to the precision of the measurement of the target polarization. The bottom subpanels show the P_{T} dependence of the average x_{F}. Data points for negative particles are slightly shifted horizontally for legibility
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Figure 2b : A^{sin\psi}_{UT} amplitudes for charged pions and kaons as a function of x_{F}. Positive (negative) particles are denoted by closed (open) symbols. When visible, the inner error bars show the statistical uncertainties, while the total ones represent the quadratic sum of statistical and systematic uncertainties. Not shown is an additional 8.8% scale uncertainty due to the precision of the measurement of the target polarization. The bottom subpanels show the x_{F} dependence of the average P_{T}. Data points for negative particles are slightly shifted horizontally for legibility
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Figure 3 : A^{sin\psi}_{UT} amplitudes for charged pions and kaons as a function of P_{T} for various slices in x_{F}. Symbol definitions and additional 8.8% scale uncertainty as in Fig. 2
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Figure 4 : A^{sin\psi}_{UT} amplitudes for charged pions and kaons as a function of x_{F} for various slices in P_{T}. Symbol definitions and additional 8.8% scale uncertainty as in Fig. 2
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Figure 5 : A^{sin\psi}_{UT} amplitudes for charged pions and kaons for the `anti-tagged' category and the two DIS subsamples with 0.2 < z < 0.7 and z > 0.7, respectively. Also shown are the relative fractions of the two DIS subsamples with respect to the total inclusive sample of the corresponding hadron species after correction for trigger efficiency. Positive (negative) particles are denoted by filled (open) symbols. Inner error bars show the statistical uncertainties and the total error bars represent statistical and systematic uncertainties added in quadrature. Not shown is an additional 8.8% scale uncertainty due to the precision of the measurement of the target polarization
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May 10, 2013
Multiplicities of charged pions and kaons from semi-inclusive deep-inelastic scattering by the proton and the deuteron
A. Airapetian et al, Phys. Rev. D87 (2013) 074029 *PDF
Eprint numbers: arXiv:1212.5407 and DESY-12-157
INFO: The covariance matrices of the provided data can be found here. DOI: 10.1103/PhysRevD.87.074029
Summary of paper for the general science reader: *PDF
SUBJECT: FRAGMENTATION
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Schematic view of the HERMES spectrometer
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Figure 2 : Born space in (x,Q²) for the multiplicities extracted
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Figure 3 : Fraction of mesons generated by the decay of exclusive vector mesons as a function of z, from PYTHIA. The widths of the bands indicate the uncertainty in the corresponding fractions. The vertical dashed lines are the limits in z used in the multiplicity extractions
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Figure 4 : Multiplicities corrected for exclusive vector mesons as a function of z from a hydrogen target (full circles) and a deuterium target (empty squares). Error bars for the statistical uncertainties are too small to be visible. The systematic uncertainties are given by the error bands
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Figure 5a : Comparison of measured Born multiplicities for a proton target with and without the correction for exclusive vector mesons as a function of z. The open (closed) circles include (exclude) exclusive vector meson production. The statistical error bars are too small to be visible
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Figure 5b : Ratios of measured Born multiplicities for a proton target with and without the correction for exclusive vector mesons as a function of z. The statistical error bars are too small to be visible
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Figure 6 : The asymmetry A^{h}_{d-p} as a function of z, for the multiplicities shown in Fig. 4. The values given by a LO calculation using fragmentation functions from DSS and parton distributions from CTEQ6L are given by the solid curves
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Figure 7 : The asymmetry A^{h}_{d-p} as a function of xB, for the pion multiplicities shown in Fig. 8. The statistical uncertainty is shown by the error bars, while the systematic uncertainty is given by the error bands
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Figure 8a : Multiplicities of pions for the proton and the deuteron as a function of Ph\perp in four z bins. Positive charge is on the left and negative charge is on the right of each panel. Uncertainties are as in Fig. 4
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Figure 8b : Multiplicities of kaons for the proton and the deuteron as a function of Ph\perp in four z bins. Positive charge is on the left and negative charge is on the right of each panel. Uncertainties are as in Fig. 4
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Figure 8c : Multiplicities of pions for the proton and the deuteron as a function of xB in four z bins. Positive charge is on the left and negative charge is on the right of each panel. Uncertainties are as in Fig. 4
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Figure 8d : Multiplicities of kaons for the proton and the deuteron as a function of xB in four z bins. Positive charge is on the left and negative charge is on the right of each panel. Uncertainties are as in Fig. 4
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Figure 8e : Multiplicities of pions for the proton and the deuteron as a function of Q² in four z bins. Positive charge is on the left and negative charge is on the right of each panel. Uncertainties are as in Fig. 4
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Figure 8f : Multiplicities of kaons for the proton and the deuteron as a function of Q² in four z bins. Positive charge is on the left and negative charge is on the right of each panel. Uncertainties are as in Fig. 4
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Figure 9 : Comparison of the vector-meson-corrected multiplicities measured on the proton for various hadrons with LO calculations using CTEQ6L parton distributions and three compilations of fragmentation functions. Also shown are the values obtained from the HERMES Lund Monte Carlo. The statistical error bars on the experimental points are too small to be visible
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Figure 10 : Comparison of the vector-meson-corrected multiplicities measured on the deuteron for various hadrons with LO calculations using CTEQ6L parton distributions and three compilations of fragmentation functions. Also shown are the values obtained from the HERMES Lund Monte Carlo. The statistical error bars on the experimental points are too small to be visible
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Jan 31, 2013
Azimuthal distributions of charged hadrons, pions, and kaons produced in deep-inelastic scattering off unpolarized protons and deuterons
A. Airapetian et al, Phys. Rev. D 87 (2013) 012010 *PDF
Eprint numbers: arXiv:1204.4161 and DESY-12-060
INFO: DOI: 10.1103/PhysRevD.87.012010
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: AZIMUTHAL
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Depiction of the azimuthal angle phi
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Figure 2 : Average kinematics for the integration range 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV, as extracted from a 4pi Monte Carlo (shown here for positive hadrons on hydrogen; other cases exhibit only minor deviations). The data in multi-dimensional bins (900 bins), as well as the covariance matrices can be found in here
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Figure 3 : Average kinematics for the integration range 0.042 < x < 0.27, 0.3 < y < 0.7, 0.2 < z < 0.6, 0.2 < P_h\perp < 0.7 GeV, as extracted from a 4pi Monte Carlo
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Figure 4 : cos 2phi amplitudes for positive (upper panels) and negative (lower panels) pions integrated over the kinematic range of 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV. Closed and open squares are for amplitudes extracted from hydrogen and deuterium targets, respectively. The inner bar represents the statistical uncertainty; the outer bar is the total uncertainty, evaluated as the sum in quadrature of statistical and systematic uncertainties. Points have been slightly shifted horizontally for visibility
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Figure 5 : cos phi amplitudes for positive (upper panels) and negative (lower panels) pions integrated over the kinematic range of 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV. Closed and open squares are for amplitudes extracted from hydrogen and deuterium targets, respectively. The inner bar represents the statistical uncertainty; the outer bar is the total uncertainty, evaluated as the sum in quadrature of statistical and systematic uncertainties. Points have been slightly shifted horizontally for visibility
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Figure 6 : cos 2phi amplitudes for positive (upper panels) and negative (lower panels) kaons integrated over the kinematic range of 0.042 < x < 0.27, 0.3 < y < 0.7, 0.2 < z < 0.6, 0.2 < P_h\perp < 0.7 GeV. Closed and open squares are for amplitudes extracted from hydrogen and deuterium targets, respectively. The inner bar represents the statistical uncertainty; the outer bar is the total uncertainty, evaluated as the sum in quadrature of statistical and systematic uncertainties. Points have been slightly shifted horizontally for visibility
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Figure 7 : cos phi amplitudes for positive (upper panels) and negative (lower panels) kaons integrated over the kinematic range of 0.042 < x < 0.27, 0.3 < y < 0.7, 0.2 < z < 0.6, 0.2 < P_h\perp < 0.7 GeV. Closed and open squares are for amplitudes extracted from hydrogen and deuterium targets, respectively. The inner bar represents the statistical uncertainty; the outer bar is the total uncertainty, evaluated as the sum in quadrature of statistical and systematic uncertainties. Points have been slightly shifted horizontally for visibility
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Figure 8 : cos 2phi amplitudes for positive (upper panels) and negative (lower panels) unidentifed hadrons integrated over the kinematic range of 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV. Closed and open squares are for amplitudes extracted from hydrogen and deuterium targets, respectively. The inner bar represents the statistical uncertainty; the outer bar is the total uncertainty, evaluated as the sum in quadrature of statistical and systematic uncertainties. Points have been slightly shifted horizontally for visibility
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Figure 9 : cos phi amplitudes for positive (upper panels) and negative (lower panels) unidentifed hadrons integrated over the kinematic range of 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV. Closed and open squares are for amplitudes extracted from hydrogen and deuterium targets, respectively. The inner bar represents the statistical uncertainty; the outer bar is the total uncertainty, evaluated as the sum in quadrature of statistical and systematic uncertainties. Points have been slightly shifted horizontally for visibility
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Figure 12 : cos 2phi amplitudes from a deuterium target for positive (upper panels) and negative (lower panels) unidentifed hadrons (triangles), pions (squares) and kaons (circles), integrated over the kinematic range 0.042 < x < 0.27, 0.3 < y < 0.7, 0.2 < z < 0.6, 0.2 < P_h\perp < 0.7 GeV. Points have been slightly shifted horizontally for visibility
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Figure 13 : cos phi amplitudes from a deuterium target for positive (upper panels) and negative (lower panels) unidentifed hadrons (triangles), pions (squares) and kaons (circles), integrated over the kinematic range 0.042 < x < 0.27, 0.3 < y < 0.7, 0.2 < z < 0.6, 0.2 < P_h\perp < 0.7 GeV. Points have been slightly shifted horizontally for visibility
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Figure 14 : Difference between the amplitudes of negative and positive pions within the kinematic range 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV. Closed and open symbols are for amplitudes extracted from hydrogen and deuterium targets, respectively. Points have been slightly shifted horizontally for visibility
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Figure 15 : Difference between the amplitudes of negative and positive kaons within the kinematic range 0.042 < x < 0.27, 0.3 < y < 0.7, 0.2 < z < 0.6, 0.2 < P_h\perp < 0.7 GeV. Closed and open symbols are for amplitudes extracted from hydrogen and deuterium targets, respectively. Points have been slightly shifted horizontally for visibility
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Figure 16 : Difference between the amplitudes of negative and positive unidentifed hadrons within the kinematic range 0.023 < x < 0.27, 0.3 < y < 0.85, 0.2 < z < 0.75 and 0.05 < P_h\perp < 1.0 GeV. Closed and open symbols are for amplitudes extracted from hydrogen and deuterium targets, respectively. Points have been slightly shifted horizontally for visibility
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Oct 14, 2012
Beam-helicity asymmetry arising from deeply virtual Compton scattering measured with kinematically complete event reconstruction
A. Airapetian et al, JHEP10(2012)042 *PDF
Eprint numbers: arXiv:1206.5683 and DESY-12-095
Summary of paper for the general science reader: *PDF
SUBJECT: DVCS
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Momenta and azimuthal angle for exclusive electroproduction of real photons in the target rest frame
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Figure 2a : Leading-order diagram for the channel ep -> ep\gamma for deeply virtual Compton scattering (DVCS) process
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Figure 2b : Leading-order diagram for the channel ep -> ep\gamma for Bethe-Heitler (BH) processe
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Figure 3 : Schematic diagram of the Hermes recoil detector (cross-section view). The Hera lepton beamis perpendicular to the paper plane. The cross section of the target cell is shown as ellipse. The tracking layers are indicated, from inside to outside: inner and outer layers (in diamond shape) of the Silicon Strip Detector (SSD), inner and outer barrels (circles) of the Scintillating Fiber Tracker (SFT). Space-points are indicated by crosses. The SSD modules are located inside the vacuum chamber (dashed circle). The Photon Detector (PD) shown as a dash-dotted circle is not used in the present analysis. The magnet (not shown) surrounds the detector assembly. Also shown are examples of tracks reconstructed from two, three, and four space-points
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Figure 4a : The momentum resolution versus momentum for proton reconstruction by using only the information on the curvature in the magnetic field (circles) and by combining the information on curvature with energy deposition in the SSD (squares)
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Figure 4b : The azimuthal-angle resolution versus momentum
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Figure 4c : The polar-angle resolution versus momentum
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Figure 5a : Distribution of the squared missing mass from experimental data for unresolved, unresolved-reference and pure exclusive event samples. The requirements applied on the squared missing mass in order to select (only) the unresolved and the unresolved-reference samples are indicated as vertical dashed-dotted lines. The exclusive signal is expected around the square of the proton mass, indicated as vertical dashed line
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Figure 5b : Left: unresolved; middle: unresolved-reference; right: pure sample. Experimental data, shown as data points (uncertainties covered by symbols), are compared to simulated data. In every panel, the contribution from BH events is indicated as dashed histogram, and the contributions from associated production and semi-inclusive background are shown as hatched histograms. The sum of the simulated distributions is shown as solid histogram
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Figure 6 : The fractional contributions from the BH process (closed symbols) and associated BH process (open symbols), for each of the exclusive samples. The fractional contributions are extracted from Monte Carlo simulations and are presented in the same kinematic binning as the asymmetry amplitudes. Symbols for the unresolved (unresolved-reference) sample are shifted to the left (right) for better visibility. If the points were plotted without such shifts, a difference would only be visible in the first -t bin
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Figure 7 : Amplitudes of single-charge beam-helicity asymmetry in DVCS shown in projections of -t, xB, and Q². Statistical uncertainties are shown by error bars. The bands represent the systematic uncertainties of the amplitudes extracted from the pure sample. A separate scale uncertainty arising from the measurement of the beam polarization amounts to 1.96%. Shown are amplitudes extracted from a) the pure sample (red circles, shown at their kinematic values), i.e., obtained with recoil-proton reconstruction; b) the unresolved-reference sample (blue triangles, shifted to the right for better visibility), i.e., without recoil-proton reconstruction but requiring its four-momentum to be in the recoil-detector acceptance; c) the unresolved sample (black stars, shifted to the left for better visibility), i.e., without requirements from recoil-detector acceptance and reconstruction. The latter two sets of amplitudes are subject to an average contribution of 14% and 12%, respectively, for associated processes
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Figure 8 : Amplitudes of single-charge beam-helicity asymmetry extracted from pure sample obtained with recoil-proton reconstruction. The amplitudes are presented in projections of -t, xB, and Q². The overall results shown in the very left panel are extracted in a single kinematic bin covering the entire kinematic acceptance. Statistical (systematic) uncertainties are represented by error bars (bands). A separate scale uncertainty arising from the measurement of the beam polarization amounts to 1.96%. The theoretical models are evaluated at the average values of the kinematics. The thickness of the VGG lines represents the range bval = 1...infinity
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Jul 5, 2012
Beam-helicity and beam-charge asymmetries associated with deeply virtual Compton scattering on the unpolarised proton
A. Airapetian et al, JHEP 07 (2012) 032 *PDF
Eprint numbers: arXiv:1203.6287 and DESY-12-040
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DVCS: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : The leading DVCS process in which an electron/positron interacts with a quark in the nucleon via a virtual photon. The quark is found in the nucleon with longitudinal momentum fraction x+xi and emits a real photon. The quark is absorbed by the nucleon withlongitudinal momentum fraction x-xi

Figure 1b : The leading Bethe-Heitler process, i.e. the emission of a real photon from the incoming or outgoing lepton. This process has the same initial and final states as DVCS

Figure 2 : Beam-helicity asymmetry amplitudes extracted separately from the unpolarised 1996-2005 (open triangles) and 2006-2007 (filled squares) hydrogen data. The error bars represent the statistical uncertainties. The error bands represent the systematic uncertainties. An additional 2.8 % and 3.4 % scale uncertainty for the 1996-2005 and 2006-2007 data respectively is present in the amplitudes due to the uncertainty of the beam polarisation measurement. The simulated fractional contribution from associated production to the yield in each kinematic bin is shown in the bottom row
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Figure 3 : Beam-charge asymmetry amplitudes extracted separately from the unpolarised 1996-2005 (open triangles) and 2006-2007 (filled squares) hydrogen data. The error bars represent the statistical uncertainties. The error bands represent the systematic uncertainties. The simulated fractional contribution from associated production to the yield in each kinematic bin is shown in the bottom row
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Figure 4 : The beam-helicity asymmetry amplitudes extracted from all the unpolarised hydrogen data recorded at HERMES from 1996 until 2007. The error bars (bands) represent the statistical (systematic) uncertainties. An additional 3.2 % scale uncertainty is present in the amplitudes due to the uncertainty of the beam polarisation measurement. Solid, dashed (KM09) and dashed-dotted lines (GGL11) show model calculations. See text for details. The simulated fractional contribution from associated production to the yield in each kinematic bin is shown in the bottom row
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Figure 5 : The beam-charge asymmetry amplitudes extracted from all the unpolarised hydrogen data recorded at HERMES from 1996 until 2007. The error bars (bands) represent the statistical (systematic) uncertainties. Theoretical calculations are shown as solid and dashed lines (KM09) or as dashed-dotted lines (GGL11). See text for details. The simulated fractional contribution from associated production to the yield in each kinematic bin is shown in the bottom row
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Figure 6 : The beam-helicity asymmetry amplitudes extracted from all the unpolarised hydrogen data recorded at HERMES from 1996 until 2007 as a function of -t for three different x_B ranges. The error bars (bands) represent the statistical (systematic) uncertainties. An additional 3.2 % scale uncertainty is present in the amplitudes due to the uncertainty of the beam polarisation measurement. The simulated fractional contribution from associated production to the yield in each kinematic bin is shown in the bottom row
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Figure 7 : The beam-charge asymmetry amplitudes extracted from all the unpolarised hydrogen data recorded at HERMES from 1996 until 2007 as a function of -t for three different x_B ranges. The error bars (bands) represent the statistical (systematic) uncertainties. The simulated fractional contribution from associated production to the yield in each kinematic bin is shown in the bottom row
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Figure 8 : The covariance matrix results for the asymmetries extracted in a single bin across the whole kinematic range. The size of the symbols in the chart reflect the magnitude of the corresponding correlation. Closed (open) symbols represent positive (negative) correlations
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Figure 9 : The beam-charge asymmetry amplitudes extracted in 4 and 6 bins
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Figure 10 : The beam-charge asymmetry amplitudes extracted in 4 and 6 bins

Mar 19, 2012
Measurement of the virtual-photon asymmetry A₂ and the spin-structure function g₂ of the proton
A. Airapetian et al, Eur. Phys. J. C 72 (2012) 1921 *PDF
Eprint numbers: arXiv:1112.5584 and DESY-11-249
INFO: DOI: 10.1140/epjc/s10052-012-1921-5
SUBJECT: G1: g2
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The spin-structure function xg2(x;Q²) of the proton as a function of Q² for selected values of x. Data from the experiments E155 and E143 are presented also. The error bars represent the quadratic sum of the statistical and systematic uncertainties. The solid curve is the result of the Wandzura-Wilczek relation
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Figure 2a : The virtual-photon asymmetry A2 of the proton as a function of x. HERMES data are shown together with data from the E155, E143, and SMC experiments. The total error bars for the HERMES, E155, and E143 experiments represent the quadratic sum of the statistical and systematic uncertainties. The statistical uncertainties are indicated by the inner error bars. The error bars for the SMC experiment represent the statistical uncertainties only. The solid curve corresponds to the Wandzura-Wilczek relation evaluated at the average Q² values of HERMES at each value of x. For the HERMES data, the closed (open) symbols represent data with < Q² > > 1 GeV² ( < Q² > < 1 GeV²)
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Figure 2b : The spin-structure function xg2 of the proton as a function of x. HERMES data are shown together with data from the E155, E143, and SMC experiments. The total error bars for the HERMES, E155, and E143 experiments represent the quadratic sum of the statistical and systematic uncertainties. The statistical uncertainties are indicated by the inner error bars. The error bars for the SMC experiment represent the statistical uncertainties only. The solid curve corresponds to the Wandzura-Wilczek relation evaluated at the average Q² values of HERMES at each value of x. For the HERMES data, the closed (open) symbols represent data with < Q² > > 1 GeV² ( < Q² > < 1 GeV²)
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Dec 12, 2011
Inclusive Measurement of Inelastic Electron and Positron Scattering on Unpolarized Hydrogen and Deuterium Targets
A. Airapetian et al, JHEP 05 (2011) 126 *PDF *PostScript
Eprint numbers: arXiv:1103.5704 and DESY-11-048
SUBJECT: F2
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Binning in (x,Q²) used in the analysis and kinematic acceptance of events. The kinematic region covered is limited by the geometrical acceptance in theta and constraints on y and W². The symbols mark the locations of the average values of (x,Q²) of each bin. The symbols A to F denote bins with increasing Q² at given x
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Figure 2 : Trigger efficiencies for data taken in the year 2000 shown separately for the top and bottom spectrometer halves. The error bars represent only statistical uncertainties. The symbols refer to the Q² bins shown in 11-066
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Figure 3 : Lepton identification efficiency (top) and hadron contamination (bottom) in the year 2000. The symbols refer to the Q² binning shown in 11-066
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Figure 4 : Percentage of charge-symmetric background, calculated from the ratio of the charge-symmetric events to the total events in each bin, for the 2000 deuterium data. The symbols refer to the Q² binning shown in 11-066
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Figure 5 : Inelastic proton differential DIS cross section multiplied by a factor Q⁴ for the purpose of illustration and scaled by powers of 1.6, in the kinematic range 0.008 < x < 0.639 and 0.2 GeV² < Q² < 20 GeV². The results are overlaid with the phenomenological parameterization GD11-P (central curves) and its uncertainty (outer curves). The error bars represent the total uncertainties calculated as the sum in quadrature of all statistical and systematic uncertainties including normalization, and are smaller than the symbols
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Figure 6 : Inelastic deuteron differential DIS cross section multiplied by a factor Q⁴ for the purpose of illustration and scaled by powers of 1.6, in the kinematic range 0.008 < x < 0.639 and 0.2 GeV² < Q² < 20 GeV². The results are overlaid with the phenomenological parameterization GD11-D (central curves) and its uncertainty (outer curves). The error bars represent the total uncertainties calculated as the sum in quadrature of all statistical and systematic uncertainties including normalization, and are smaller than the symbols
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Figure 7 : HERMES data for F^p₂ together with world data in the kinematic range 0.008 < x < 0.679 and 0.02 GeV² < Q² < 20 GeV². The results are overlaid with the phenomenological parameterization GD11-P (black solid central curve) and its uncertainty (outer curves). A bin-centering correction is applied to the data in order to match the central values of the x bins. The values of F_p² are scaled by powers of 1.6. Inner error bars are statistical uncertainties, while outer error bars are total uncertainties calculated as the sum in quadrature of all statistical and systematic uncertainties including normalization
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Figure 8 : HERMES data for F^d₂ together with world data in the kinematic range 0.008 < x < 0.679 and 0.02 GeV² < Q² < 20 GeV². The results are overlaid with the phenomenological parameterization GD11-D (black solid central curve) and its uncertainty (outer curves). A bin-centering correction is applied to the data in order to match the central values of the x bins. The values of F_d² are scaled by powers of 1.6. Inner error bars are statistical uncertainties, while outer error bars are total uncertainties calculated as the sum in quadrature of all statistical and systematic uncertainties including normalization
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Figure 9 : HERMES data for the photon-proton cross section as a function of W², together with world data and the results from the GD11-P fit (central curves) and its uncertainties (outer curves), in bins of Q². The data points denoted real photon are for photoproduction. Inner error bars are statistical uncertainties, while outer error bars are total uncertainties calculated as the sum in quadrature of all statistical and systematic uncertainties including normalization
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Figure 10 : HERMES data for the photon-deuteron cross section as a function of W², together with world data and the results from the GD11-D fit (central curves) and its uncertainties (outer curves), in bins of Q². The data points denoted real photon are for photoproduction. Inner error bars are statistical uncertainties, while outer error bars are total uncertainties calculated as the sum in quadrature of all statistical and systematic uncertainties including normalization
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Figure 11 : The Q² dependence of sigma_d/sigma_p for data from SLAC, HERMES, EMC, NMC, JLAB and BCDMS in bins of x. The error bars on the data points represent total uncertainties. The data points are overlaid with the results from the fit described by the functional form A(x) + B(x) ln Q² (blue solid line), with the unity line (red dashed) and with the ratio of the GD11-D over GD11-P fits (green dash-dotted line)
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Figure 12 : Same as 11-072, HERMES data for F^p₂ together with world data as a function of Q², but in the kinematic region where there is only HERMES data
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Figure 13 : Same as 11-073, HERMES data for F^d₂ together with world data as a function of Q², but in the kinematic region where there is only HERMES data
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Figure 14 : Same as 11-072, HERMES data for F^p₂ together with world data as a function of Q², but in the kinematic region where there is overlap with existing data
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Figure 15 : Same as 11-073, HERMES data for F^d₂ together with world data as a function of Q², but in the kinematic region where there is overlap with existing data
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Figure 16 : The world data on F^p₂ as a function of Q² in the kinematic region 0.00006 < x < 0.85 and 0.03 < Q² < 1000 GeV², overlapped with the phenomenological parameterization GD11-D
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Figure 17 : The world data on F^d₂ as a function of Q² in the kinematic region 0.0008 < x < 0.85 and 0.03 < Q² < 300 GeV², overlapped with the phenomenological parameterization GD11-D
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Sep 23, 2011
Multidimensional Study of Hadronization in Nuclei
A. Airapetian et al, Eur. Phys. J. A 47 (2011) 113 *PDF
Eprint numbers: arXiv:1107.3496 and DESY-11-120
Summary of paper for the general science reader: *PDF
SUBJECT: HADRON-ATTENUATION
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Dependence of R^h_A on nu for positively charged hadrons for three slices in z. The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In addition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Figure 2 : Dependence of R^h_A on nu for negatively charged hadrons for three slices in z. The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In addition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Figure 3 : Dependence of R^h_A on z for positively charged hadrons for three slices in nu. The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In addition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Figure 4 : Dependence of R^h_A on z for negatively charged hadrons for three slices in nu. The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In addition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Figure 5 : Dependence of R^h_A on p_t² for positively charged hadrons for three slices in z. The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In addition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Figure 6 : Dependence of R^h_A on z for positively charged hadrons for three slices in p_t². The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In addition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Figure 7 : Dependence of R^h_A on z for negatively charged hadrons for three slices in p_t². The inner and outer error bars indicate the statistical and total uncertainties, respectively. For the latter the statistical and systematic bin-to-bin uncertainties were added in quadrature. In a201012_Helamprho/data_filesddition, scale uncertainties of 3%, 5%, 4%, and 10% are to be considered for pions, kaons, protons and antiprotons, respectively
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Sep 15, 2011
Measurement of double-spin asymmetries associated with deeply virtual Compton scattering on a transversely polarized hydrogen target
A. Airapetian et al, Phys. Lett. B 704 (2011) 15-23 *PDF *PostScript
Eprint numbers: arXiv:1106.2990 and DESY-11-100
Summary of paper for the general science reader: *PDF
SUBJECT: DVCS: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Momenta and azimuthal angles for exclusive real-photon electroproduction in the target rest frame. The quantity phi denotes the angle between the lepton scattering plane containing the three-momenta k and k' of the incoming and outgoing lepton and the photon production plane correspondingly defined by the vector q=k-k' and the momentum q' of the real photon. The symbol phi_S denotes the angle between the lepton scattering plane and S_\perp , the component of the target polarization vector that is orthogonal to q . These definitions are consistent with the Trento conventions
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Figure 2 : Charge-difference double-spin asymmetry amplitudes describing the dependence of the interference term on transverse target polarization in combination with beam helicity and beam charge extracted from hydrogen target data. The error bars (bands at the bottom of the panels) represent the statistical (systematic) uncertainties. There is an additional overall 8.6 % scale uncertainty arising from the uncertainties in the measurements of the beam and target polarizations. The curves show the results of theoretical calculations using the VGG double-distribution model with a Regge ansatz for modeling the t dependence of GPDs. The widths of the curves represent the effect of varying the total angular momentum J_u of u-quarks between 0.2 and 0.6, with J_d=0. The bottom row shows the fractional contribution of associated BH production as obtained from a MC simulation
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Figure 3 : Charge-averaged double-spin asymmetry amplitudes describing the dependence of the sum of squared DVCS and BH terms on transverse target polarization in combination with beam helicity extracted from hydrogen target data. The error bars (bands at the bottom of the panels) represent the statistical (systematic) uncertainties. There is an additional overall 8.6 % scale uncertainty arising from the uncertainties in the measurements of the beam and target polarizations. The curves and the bottom row of panels have the same meaning as in 11-084
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Figure 4 : Correlation matrix for all fitted asymmetry amplitudes. The closed symbols represent positive values, while the open ones are for negative values. The area of the symbols represents the size of the correlation
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May 2, 2011
Ratios of Helicity Amplitudes of Exclusive rho⁰ Electroproduction
A. Airapetian et al, EPJ C 71 (2011) 1609 *PDF *PostScript
Eprint numbers: arXiv:1012.3676 (hep-ex) and DESY-10-229
Summary of paper for the general science reader: *PDF
SUBJECT: EXCLUSIVE: rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Definition of angles in the process eN -> e' rho⁰ N' -> e' pi^+ pi^- N'. Here Phi is the angle between the rho⁰ production plane and the lepton scattering plane in the CM system of virtual photon and target nucleon. The variables \theta and \phi are respectively the polar and azimuthal angles of the decay pi^+ in the rho⁰-meson rest frame, with the Z axis being anti-parallel to the outgoing nucleon momentum
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Figure 2 : Comparison of SDME and amplitude methods. Red squares show the results of the SDME analysis. Blue circles (amplitude method) are obtained in the present work from amplitude ratios fitted directly to the three-dimensional angular distribution in every Q² and -t' bin. The proton data at < Q² > = 3 GeV², < -t' > = 0.019 GeV² are presented. Yellow bands mark those SDMEs that are non-zero in the SCHC approximation. Total uncertainties are depicted
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Figure 3 : Comparison of SDME and amplitude methods. Red squares show the results of the SDME analysis. Blue circles (amplitude method) are obtained in the present work from amplitude ratios fitted directly to the three-dimensional angular distribution in every Q² and -t^' bin. The deuteron data at < Q²> = 1.19 GeV², <-t'>= 0.145 GeV² are presented. Yellow bands mark those SDMEs that are non-zero in the SCHC approximation. Total uncertainties are depicted
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Figure 4a : The Q² dependence of Re( T_{11}/T_{00} ) for proton data, showing the result for the 16 (Q², -t') bins. Inner error bars show the statistical uncertainty and the total error bars represent statistical and systematic uncertainties added in quadrature. The data is fitted. Central lines are calculated with the fitted values of parameters, while the dashed lines correspond to one standard deviation of the curve parameter. Except for the second -t' bin, the data points are shifted for better visibility
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Figure 4b : same as 10-082 but for deuteron
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Figure 5a : The Q² dependence of Re(T_{11}/T_{00} for proton and deuteron data. Points show the amplitude ratios after averaging over four -t^' bins. The parameterization of the curves obtained from combined proton and deuteron data is also shown
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Figure 5b : same as 10-84 but for Im( T_{11}/T_{00})
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Figure 6a : The Q² dependence of the phase difference \delta_{11} (left panel) between the amplitudes T_{11} and T_{00} obtained for proton and deuteron data. Inner error bars show the statistical uncertainty and the outer ones show the statistical and systematic uncertainties added in quadrature. The fitted parameterization is also shown. The central lines are calculated with the fitted values of the parameters, while the dashed lines correspond to one standard deviation in the uncertainty of the curve parameter
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Figure 6b : same as 10-086 but for \delta_{01}
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Figure 7a : The t' dependence of Q* Re(T_{11}/T_{00}) for proton and deuteron data. Points show the amplitude ratios after averaging over four Q² bins. The straight lines show the value of the fitted parameters. The meaning of the error bars and the explanation of the curves are the same as for 10-086
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Figure 7b : The same as 10-088 but for Im(T_{11}/T_{00}) / Q
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Figure 8a : The dependences of |U_{11}/T_{00}| on Q² and t' for proton and deuteron data. The points show the amplitude ratios after averaging over -t' binsl. The inner error bars show the statistical uncertainty and the outer ones show the statistical and systematic uncertainties added in quadrature. The results fitting the combined data set with a constant (central line), |U_{11}/T_{00}|=g, are shown. The dashed lines correspond to one standard deviation in the total uncertainty
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Figure 8b : The same as 10-090 but after averaging over Q²
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Figure 9a : The t' dependence of Re(T_{01}/T_{00}) for proton and deuteron data. Points show amplitude ratios after averaging over $Q²$ bins. Inner error bars show the statistical uncertainty and the outer bars show statistical and systematic uncertainties added in quadrature. Central lines are calculated with fitted values of parameters, while the dashed lines correspond to one standard deviation of the curve parameter
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Figure 9b : The same as 10-092 but for Q * Im (T_{01}/T_{00} )
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Figure 10a : The Q² dependence of Re(T_{01}/T_{00}) / \sqrt{-t'} for proton and deuteron data. Points show amplitude ratios after averaging over -t' bins. Inner error bars show the statistical uncertainty and the outer bars show statistical and systematic uncertainties added in quadrature. Central lines are calculated with fitted values of parameters, while the dashed lines correspond to one standard deviation of the curve parameter
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Figure 10b : The same as 10-094 but for Im(T_{01}/T_{00}) / \sqrt{-t'}
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Figure 11a : The Q² dependence of Re(T_{10}/T_{00}) / \sqrt{-t'} for proton and deuteron data. Points show amplitude ratios after averaging over -t' bins. Inner error bars show the statistical uncertainty and the outer ones indicate statistical and systematic uncertainties added in quadrature. Central lines are calculated with the fitted values of parameters, while the dashed lines correspond to one standard deviation of the curve parameter
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Figure 11b : The same as 10-096 but for Im(T_{10}/T_{00})/\sqrt{-t'}
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Figure 12a : The Q² dependence of Re(T_{1-1}/T_{00})/(-t') for proton and deuteron data. Points show amplitude ratios after averaging over $-t'$ bins. Inner error bars show the statistical uncertainty and the outer ones indicate statistical and systematic uncertainties added in quadrature. Central lines are calculated with the fitted values of parameters, while the dashed lines correspond to one standard deviation of the curve parameter
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Figure 12b : The same as 10-098 but for Im(T_{1-1}/T_{00}) / (-t')
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Figure 13a : The kinematic dependences of Re(T_{11}/T_{00}) and for proton and deuteron data from HERMES and H1. Inner error bars show the statistical uncertainty and the outer ones indicate statistical and systematic uncertainties added in quadrature
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Figure 13b : The same as 10-100 but for Re(T_{01}/T_{00})
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Oct 19, 2010
Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on a longitudinally polarized deuterium target
A. Airapetian et al, Nucl. Phys. B842 (2011) 265-298 *PDF
Eprint numbers: arXiv:1008.3996 (hep-ex) and DESY-10-136
Summary of paper for the general science reader: *PDF
SUBJECT: DVCS: deuterium
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : Results from the present work (red filled squares) representing single-charge beam-helicity asymmetry amplitudes describing the dependence of the sum of squared DVCS and interference terms on the beam helicity, for a tensor polarization of P_zz=0.827 . The black open squares represent charge-difference amplitudes from only the interference term, extracted from unpolarized deuterium data. The error bars represent the statistical uncertainties, while the coarsely hatched (open) bands represent the systematic uncertainties of the filled (open) squares. There is an additional overall 1.9% (2.4%) scale uncertainty arising from the uncertainty in the measurement of the beam polarization in the case of polarized (unpolarized) deuterium data. The points for unpolarized deuterium data are slightly shifted to the left for better visibility. The finely hatched band shows the results of theoretical calculations for the combination of incoherent scattering on proton and neutron, using variants of the VGG double-distribution model with a Regge ansatz for modeling the t dependence of GPDs
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Figure 1b : Simulated yield fractions of coherent and resonant production
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Figure 2 : Single-charge target-spin asymmetry amplitudes describing the dependence of the sum of squared DVCS and interference terms on the target vector polarization, for a tensor polarization of P_zz=0.827. The squares represent the results from the present work. The triangles denote the corresponding amplitudes extracted from longitudinally polarized hydrogen data. The error bars (bands) represent the statistical (systematic) uncertainties. The finely hatched bands have the same meaning as in 10-064. There is an additional overall 4.0% (4.2%) scale uncertainty arising from the uncertainty in the measurement of the target polarization in the case of deuterium (hydrogen). The points for hydrogen are slightly shifted to the left for better visibility
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Figure 3 : Single-charge double-spin asymmetry amplitudes describing the dependence of the sum of Bethe-Heitler, squared DVCS and interference terms on the product of the beam helicity and target vector polarization, for a tensor polarization of P_zz=0.827. The plotted symbols and bands have the same meaning as in 10-060. There is an additional overall 4.4% (5.3%) scale uncertainty arising from the uncertainties in the measurement of the beam and target polarizations in the case of deuterium (hydrogen) data
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Figure 4 : Results representing single-beam-helicity charge asymmetry amplitudes (red filled squares) for P_ell=-0.530 and a tensor polarization of P_zz=0.827. The black open squares are A_C^{\cos(n\phi)} amplitudes extracted from data recorded with an unpolarized beam and unpolarized deuterium target. The error bars and bands and finely hatched bands have the same meaning as in 10-060. The points for unpolarized deuterium data are slightly shifted to the left for better visibility. There is an additional overall 2.2% scale uncertainty arising from the uncertainty in the measurement of the beam polarization
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Figure 5 : Kinematic dependence of the charge-averaged single-beam-helicity target-spin asymmetry amplitudes for P_ell=-0.530 and a tensor polarization of P_zz=0.827. The plotted symbols and bands have the same meaning as in 10-060. There is an additional overall 5.3% (5.7%) scale uncertainty for the extracted amplitudes arising from the uncertainties in the measurement of the target (beam and target) polarizations
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Figure 6 : Kinematic dependence of the single-beam-helicity beam-charge $\otimes$ target-spin asymmetry amplitudes for P_ell=-0.530 and a tensor polarization of P_zz=0.827. The plotted symbols and bands have the same meaning as in 10-060. There is an additional overall 5.3% (5.7%) scale uncertainty for the extracted amplitudes arising from the uncertainties in the measurement of the target (beam and target) polarizations
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Sep 5, 2010
Leading Order Determination of the Gluon Polarization from high-p_T Hadron Electroproduction
A. Airapetian et al, JHEP 08 (2010) 130 *PDF *PostScript
Eprint numbers: arXiv:1002.3921(hep-ex) and DESY-10-021
Summary of paper for the general science reader: *PDF
SUBJECT: HIGH-PT
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Feynman diagrams for hard subprocesses: a) \ordera{0} DIS, b) \ordera{1} Photon-Gluon Fusion, and c) \ordera{1} QCD Compton scattering
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Figure 2 : Measured asymmetry for the anti-tagged category of events for positive (left) and negative (right) inclusive hadrons from hydrogen (top) and deuterium (bottom) targets as a function of p_{T(beam)}. The uncertainties are statistical only. There is an overall normalization uncertainty of 5.2% (3.9%) for hydrogen (deuterium). The curves show the Monte Carlo asymmetries for three different fixed values assumed for the gluon polarization
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Figure 3 : Measured asymmetry for the tagged category of events for positive (left) and negative (right) inclusive hadrons from hydrogen (top) and deuterium (bottom) targets as a function of p_{T(\gamma^*)}. The uncertainties are statistical only. There is an overall experimental normalization uncertainty of 5.2% (3.9%) for hydrogen (deuterium). The curves show the Monte Carlo asymmetries for three different fixed values assumed for the gluon polarization
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Figure 4 : Measured asymmetry for hadron pairs produced from hydrogen (left) and deuterium (right) targets as a function of the minimum value of $\sum{p_{T(beam)}^2}$. The uncertainties are statistical only. There is an overall experimental normalization uncertainty of 5.2% (3.9%) for hydrogen (deuterium). The curves show the Monte Carlo asymmetries for three different values assumed for the gluon polarization
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Figure 5 : Contributions to hard p interactions: (a) VMD, (b) direct, and (c) anomalous. Only the basic graphs are illustrated; additional partonic activity is allowed in all three processes. The presence of spectator jets has been indicated by dashed lines, while full lines show partons that (may) give rise to high-p_t jets. The gray ovals represent multiparton wave functions. Anomalous states are built up from a perturbatively given q \bar q fluctuation, while VMD fluctuations allow no simple perturbative representation
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Figure 6 : Top panels: Measured cross section in the HERMES acceptance for tagged hadrons as a function of x_B (left), Q² (middle), and z (right) for positive (full points) and negative hadrons (open points) using a deuterium target. The lines show the tuned Pythia 6.2 calculation. Bottom panels: The corresponding ratios of the Pythia calculation to the measured cross section
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Figure 7 : Cross sections for inclusive pi⁰ production from resolved photon, QCDC, and PGF processes simulated using Pythia (solid lines) compared to the LO pQCD calculations (full points). Simulation and calculation are done in the collinear approach at Q² < 0.01 GeV², 0.2 < y < 0.9. Green/Grey lines: subprocess cross sections after varying the renormalization and factorization scales by factors of 1/2and 2 in the simulation
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Figure 8 : The simulated cross section for inclusive pi⁰ production from the PGF subprocess vs. p_{T(beam)}, \hat{p}_T², and x for Q² < 0.01 GeV², 0.2 < y < 0.9. The simulations are done using the collinear approach ((green/gray) solid line), the collinear approach together with intrinsic k_T for the partons in nucleon and photon (dashed line), and with intrinsic k_T together with fragmentation transverse momenta (solid line)
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Figure 9 : Left panels: The measured double-spin inclusive asymmetry A_\parallel (full points) and two MC asymmetries (solid and dashed lines) based on different assumptions for the low-p_T subprocess asymmetry (top) and the process fractions vs. x_B (bottom) for tagged events on a hydrogen target. Right panels: Double-spin asymmetry vs. p_{T(beam)} for anti-tagged hadron on a hydrogen (top) and deuterium (bottom) target
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Figure 10 : The cross sections and subprocess contributions, in the HERMES acceptance as a function of p_{T(beam)} for the anti-tagged category of events and a deuterium target (left: positively charged hadrons, right: negatively charged hadrons). Top: The measured cross section and that generated by Pythia . Second row: The ratio of these two cross sections. Also shown is the effect of the k-factor. Third row: The subprocess fractions from Pythia. Bottom two rows: The asymmetries and the asymmetries weighted with the subprocess fractions for each subprocess and for the gluon PDFs
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Figure 11 : The cross sections and subprocess contributions, in the HERMES acceptance, as a function of p_{T(\gamma^*)} for the tagged category of events and a deuterium target (left: positively charged hadrons, right: negatively charged hadrons). Top: The measured cross section and that generated by Pythia . Second row: The ratio of these two cross sections. Third row: The subprocess fractions from Pythia. Bottom two rows: The asymmetries and the asymmetries weighted with the subprocess fractions for each subprocess and for the gluon PDFs
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Figure 12 : The cross sections and subprocess contributions, in the HERMES acceptance, as a function of the minimum value of \sum{p_{T(beam)}^2} for the production of inclusive hadron pairs on a deuterium target. Top: The measured cross section and that generated by \Pythia. Second row: The ratio of these two cross sections. Third row: The subprocess fractions from \Pythia. Bottom two rows: The asymmetries and the asymmetries weighted with the subprocess fractions for each subprocess and for the gluon PDFs
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Figure 13 : The range of generated x for different values of p_{T(beam)} calculated by \Pythia for all signal processes, for the anti-tagged category of events and a deuterium target
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Figure 14 : The correlation of the average hard scattering < \hat p_T² > of all signal subprocesses as calculated by \Pythia with the hadron p_T for inclusive hadrons as calculated for the experimental data for the deuterium target. Left: tagged category; Center: anti-tagged category; Right: hadron pairs category. The dotted line goes along < \hat{p}_T² > = p_T²(h) (< \hat{p}_T² > = \sum{p_T²}/2) and the vertical dashed line shows the minimum p_T (\sum{p_T²}) used for the analysis
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Figure 15 : The value of \dggpfact\ determined in the anti-tagged category for protons (top) and deuterons (bottom) and positive (full points) and negative (open points) hadrons as a function of p_T. Also shown are the values for the tagged (squares) and pairs (triangle) category at their average respective p_T. The uncertainties shown are statistical only
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Figure 16 : Measured asymmetries with statistical uncertainties in four p_T bins for the anti-tagged category and a deuterium target, compared to calculated asymmetries using the two functions
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Figure 17 : Functional forms used with the values and statistical uncertainty bands from the fits. Light shaded area: the total x range spanned by the data; dark shaded area: the range in x where the preponderance of the data lies
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Figure 18 : The light gray band shows the total uncertainty of deltaG / G (x) vs. x with the statistical and total systematic uncertainty added in quadrature. The point shown represents delta G/G (< x >) at < x >=0.22. The inner error bar represents the statistical uncertainty and the outer the total uncertainty obtained by adding statistical and total systematic uncertainty in quadrature
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Figure 19 : The gluon polarization deltaG / G (< x >) from HERMES extracted with fct.~1 (< x > = 0.22, < \mu² > = 1.35 GeV²) compared to the ones from COMPASS (low Q²: \mu²=3 GeV², high Q²: \mu²=2.4 GeV², open charm: \mu²=13 GeV²) and SMC (\mu²=3.6 GeV²) including statistical uncertainties (inner error bars) and total uncertainties (outer error bars). The x region of the data is indicated by the horizontal bars. Fit function fct.~1 is shown over the full x range spanned by the HERMES data. Also shown are a sample of curves from NLO pQCD fits (DSSV, and BB-09) at \mu²=1.5 GeV². For clarity only the central values are shown
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Aug 26, 2010
Effects of transversity in deep-inelastic scattering by polarized protons
A. Airapetian et al, Phys. Lett. B 693 (2010) 11-16 *PDF *PostScript
Eprint numbers: arXiv:1006.4221 (hep-ex) and DESY-10-087
Summary of paper for the general science reader: *PDF
SUBJECT: TRANSVERSE: collins
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The definition of the azimuthal angles phi and phi_S relative to the lepton scattering plane
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Figure 2 : Collins amplitudes for pions and charged kaons as a function of x, z or P_h\perp. The systematic uncertainty is given as a band at the bottom of each panel. In addition there is a 7.3% scale uncertainty from the accuracy in the measurement of the target polarization
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Figure 2a : Same as 10-036 but for pions only
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Figure 2b : Same as 10-036 but the kaon panels only
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Figure 3a : Collins amplitudes for pi⁺ as functions of x. The Q² range for each i-bin in x was divided into the two regions above and below the average Q² of that bin (< Q²(x_i) >). The bottom panels show the x-dependence of the average Q²
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Figure 3b : Collins amplitudes for pi^- as functions of x. The Q² range for each i-bin in x was divided into the two regions above and below the average Q² of that bin (< Q²(x_i) >). The bottom panels show the x-dependence of the average Q²
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Figure 3c : Same as 10-032 but as the plot appears in the original paper
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Jun 16, 2010
Exclusive Leptoproduction of Real Photons on a Longitudinally Polarised Hydrogen target
A. Airapetian et al, JHEP 06 (2010) 019 *PDF *PostScript
Eprint numbers: arXiv:1004.0177 (hep-ex) and DESY-10-046
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DVCS: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Amplitudes of the target-spin asymmetry A_UL sensitive to a combination of the Interference and squared-DVCS terms, for positrons incident on longitudinally polarised protons, as projections in -t, x_B, and Q². The leftmost column shows the asymmetry values when the extraction is performed in a single bin across the entire kinematic range of the data set. The error bars (open red bands) show the statistical (systematic) uncertainties and the solid blue bands represent the predictions from the ``VGG Regge'' GPD model.. There is an additional 4.2% scale uncertainty due to the precision of the measurement of the target polarisation. The fractional contributions from resonance production estimated from an MC model are presented in the bottom panel
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Figure 2 : Amplitudes of the double-spin asymmetry A_LL sensitive to the Interference, squared-DVCS and squared-BH terms in the scattering amplitude, for polarised positrons incident on longitudinally polarised protons, as projections in -t, x_B, and Q². The leftmost column shows the asymmetry values when the extraction is performed in a single bin across the entire kinematic range of the data set. The error bars (open red bands) show the statistical (systematic) uncertainties and the solid blue bands represent the theoretical predictions from the ``VGG Regge'' GPD model. There is an additional 5.3% scale uncertainty due to the precision of the measurement of the beam and target polarisations. The fractional contributions from resonance production estimated from an MC model are presented in the bottom panel
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Mar 8, 2010
Nuclear-mass dependence of beam-helicity and beam-charge azimuthal asymmetries in DVCS
A. Airapetian et al, Phys. Rev. C 81 (2010) 035202 *PDF
Eprint numbers: arXiv:0911.0091 (hep-ex) and DESY-09-190
Summary of paper for the general science reader: *PDF
SUBJECT: DVCS: nuclear
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Distributions in squared missing mass (DVCS) from data using positron (filled circles) or electron (empty circles) beams and a xenon target compared to a MC simulation (solid line). The latter includes coherent Bethe--Heitler (BH) (dashed line), incoherent BH (short-dashed line) and associated BH (filled area) processes as well as semi-inclusive background (dash--dotted line). The two vertical solid lines enclose the selected exclusive region for the positron data
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Figure 2 : Distribution (points) of DVCS events selected in the exclusive region as function of -t compared to a MC simulation (solid line). The latter includes coherent Bethe-Heitler (BH) (dashed line), incoherent BH (dotted line) and associated BH (filled area) processes. Background from semi--inclusive neutral meson production is not included
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Figure 3 : The cos phi amplitude of the DVCS beam-charge asymmetry for hydrogen, krypton and xenon as function of t. The error bars (bands) represent the statistical (systematic) uncertainties
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Figure 4 : The sin phi amplitude of the DVCS beam-helicity asymmetry sensitive to the squared DVCS amplitude for hydrogen, krypton and xenon as function of $t$. The error bars (bands) represent the statistical (systematic) uncertainties. This amplitude is subject to an additional 3.4\% maximal scale uncertainty arising from beam polarimetry
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Figure 5 : The t dependence of the $sin phi$ amplitude of the DVCS beam-helicity asymmetry sensitive to the interference term, A_{LU,I}^{sin phi}, for hydrogen, krypton and xenon (full symbols) or to a linear combination of the interference and the squared DVCS amplitude, A_{LU,+}^{sin phi}, for helium, nitrogen and neon (open symbols). The error bars (bands) represent the statistical (systematic) uncertainties. This amplitude is subject to an additional 3.4\% maximal scale uncertainty arising from beam polarimetry
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Figure 6 : Nuclear-mass dependence of the cos phi amplitude of the DVCS beam-charge asymmetry for the coherent-enriched (upper panel) and incoherent-enriched (lower panel) data samples for hydrogen, krypton and xenon. The coherent-enriched samples have a purity of about 67% and the incoherent-enriched samples a purity of about 60%. The inner error bars represent the statistical uncertainty and the full bars the quadratic sum of statistical and systematic uncertainties
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Figure 7 : Nuclear-mass dependence of the sin phi amplitude of the DVCS beam-helicity asymmetry for the coherent-enriched (upper panel) and incoherent-enriched (lower panel) data samples. The coherent-enriched samples have a purity of about 67% except for He with 34%, and the incoherent-enriched samples a purity of about 60%. The inner error bars represent the statistical uncertainty and the full bars the quadratic sum of statistical and systematic uncertainties. This amplitude is subject to an additional 3.4% maximal scale uncertainty arising from beam polarimetry
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Figure 8 : The cos phi amplitude of the DVCS beam-charge asymmetry for hydrogen, krypton and xenon as function of t. The inner error bars represent the statistical uncertainty and the full bars the quadratic sum of statistical and systematic uncertainties. The purity of the coherent-enriched Kr and Xe samples is indicated for the two t bins
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Figure 9 : The sin phi amplitude of the DVCS beam-helicity asymmetry sensitive to the interference term for hydrogen, krypton and xenon as function of t. This amplitude is subject to an additional 3.4% maximal scale uncertainty arising from beam polarimetry. Otherwise as entry 10-008
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Jan 23, 2010
Transverse momentum broadening of hadrons produced in semi-inclusive deep-inelastic scattering on nuclei
A. Airapetian et al, Phys. Lett. B 684 (2010) 114-118 *PDF *PostScript
Eprint numbers: arXiv:0906.2478 (hep-ex) and DESY-09-082
INFO: A file with DC70 answers to comments on the 1st circulation has been uploaded.
Summary of paper for the general science reader: *PDF
SUBJECT: HADRON-ATTENUATION: pt broadening
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The pt broadening for positively and negatively charged pions and positively charged kaons as a function of atomic mass number A. The inner error bars represent the stataistical uncertainties; the total bars represent the total uncertainty, obtained by adding statistical and sytematic uncertainties in quadrature
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Figure 2 : The nu, Q², xB, and z dependences of the average squared transverse momentum of the detected hadron type (pi⁺, pi^-, or K⁺) for the deuterium target (top row), and pt broadening (remaining rows) for pi⁺ and pi^- produced on He, Ne, Kr, and Xe targets, and for K⁺ produced on a Xe target (bottom row). The inner error bars represent the stataistical uncertainties; the total bars represent the total uncertainty, obtained by adding statistical and sytematic uncertainties in quadrature
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Jan 14, 2010
Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on an unpolarized deuterium target
A. Airapetian et al, Nucl. Phys. B 829 (2010) 1-27 *PDF
Eprint numbers: arXiv:0911.0095 (hep-ex) and DESY-09-189
Summary of paper for the general science reader: *PDF
SUBJECT: DVCS: deuterium
CITATIONS: SPIRES at SLAC, DESY

Figure 3 : The deuteron elastic form factors. See caption of Fig. 3 for more details
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Figure 4 : The measured distribution of electroproduced real-photon events versus the squared missing mass M_X². The solid curve represents a Monte Carlo simulation. See caption of Fig. 4 for more details
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Figure 5 : Distribution in the constrained Mandelstam variable t_c of events selected in the exclusive region of M_X². See caption of Fig. 5 for more details
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Figure 6 : Amplitudes of the DVCS beam-charge asymmetry in 6 bins of -t_c, x_N, or Q² on an unpolarized deuterium target. The error bars (bands) represent the statistical (systematic) uncertainties. Also included are VGG model calculations and the simulated fractions of coherent and resonant production in each kinematic bin
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Figure 7 : Leading amplitudes of the DVCS beam-helicity asymmetries in 6 bins of -t_c, x_N, or Q² on an unpolarized deuterium target. The amplitude in the top row is sensitive to the squared DVCS term, while the amplitudes in the 2nd and 3rd row are sensitive to the Bethe-Heitler/DVCS interference term. There is an overall 2.4% scale uncertainty arising from the uncertainty in the measurement of the beam polarization. The error bars (bands) represent the statistical (systematic) uncertainties. Also included are VGG model calculations
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Figure 8 : The cos(0\phi) amplitudes of the DVCS beam-helicity asymmetries that are included as a consistency test in the maximum likelihood fit
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Figure 9 : Amplitudes of the DVCS beam-charge asymmetry in 6 bins of -t_c, x_N, or Q² on an unpolarized deuterium target and on an unpolarized hydrogen target. The error bars (bands) represent the statistical (systematic) uncertainties
*Colour (eps)

Figure 10 : Amplitudes of the DVCS beam-helicity asymmetries that are sensitive to the squared DVCS term in 6 bins of -t_c, x_N, or Q² on an unpolarized deuterium target and on an unpolarized hydrogen target. The error bars (bands) represent the statistical (systematic) uncertainties
*Colour (eps)

Figure 11 : Amplitudes of the DVCS beam-helicity asymmetries that are sensitive to the Bethe-Heitler/DVCS interference term in 6 bins of -t_c, x_N, or Q² on an unpolarized deuterium target and on an unpolarized hydrogen target. The error bars (bands) represent the statistical (systematic) uncertainties
*Colour (eps)

Dec 12, 2009
Search for a Two-Photon Exchange Contribution to Inclusive Deep-Inelastic Scattering
A. Airapetian et al, Phys. Lett. B 682 (2010) 351-354 *PDF *PostScript
Eprint numbers: arXiv:0907.5369 and DESY 09-117
INFO: This version has the updated author list
Summary of paper for the general science reader: *PDF
SUBJECT: TRANSVERSE: inclusive
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The sin phi_S amplitudes of the inclusive asymmetry A_UT in dependence of x_B, measured with an electron beam (top) and a positron beam (center). The open (closed) circles identify the data with Q² < 1 GeV² (Q² > 1 GeV²). The error bars show the statistical uncertainties, while the error boxes show the systematic uncertainties. The asymmetries integrated over x_B are shown on the left. Bottom panel: average Q² vs. x_B from data (squares), and the fraction of elastic background events to the total event sample from a Monte Carlo simulation (triangles)
*Colour (eps) *Data

Dec 12, 2009
Single-spin azimuthal asymmetry in exclusive electroproduction of pi⁺ mesons on transversely polarized protons
A. Airapetian et al, Phys. Lett. B 682 (2010) 345-350 *PDF
Eprint numbers: arXiv:0907.2596 and DESY 09-106
Summary of paper for the general science reader: *PDF
SUBJECT: EXCLUSIVE: pion
CITATIONS: SPIRES at SLAC, DESY

Figure 0 : Top panel: for the suqared missing mass dependence of the normalised yield N_pi^+ and N_pi^- for data (points) and Pythia Monte Carlo (histograms). Middle panel: the difference N_pi^+-N_pi^- of the distributions of the top panel (including Pythia MC). Bottom panel: as the middle panel, but with an MC histogram from the exclusive event generator normalised to data. The inner error bars represent the statistical uncertainty and the outer error bars represent the quadratic sum of statistical and systematic uncertainties
*Colour *Colour (eps) *Data

Figure 1 : The set of six Fourier amplitudes (A_{UT,\ell}) describing the sine modulations of the single-spin azimuthal asymmetry for unpolarized (U) beam and transverse (T) target polarization, in bins of -t', x_B, and Q². The error bars (bands) represent the statistical (systematic) uncertainties. The results receive an additional 8.2% scale uncertainty corresponding to the target polarization uncertainty
*Colour *Colour (eps) *Data

Figure 2 : Model predictions for the sin(phi-phi_S) Fourier amplitude as a function of -t'. The curves represents predictions of GPDmodel calculations. The full circles show the values of A^sin(phi-phi_S)_{UT,\ell} is taken from Fig. 1 (entry 09-090). The error bars (bands) represent the statistical (systematic) uncertainties
*Colour *Colour (eps) *Data

Nov 19, 2009
Separation of contributions from deeply virtual Compton scattering and its interference with the Bethe--Heitler process in measurements on a hydrogen target
A. Airapetian et al, JHEP 11 (2009) 083 *PDF *PostScript
Eprint numbers: arXiv:0909.3587 and DESY-09-143
Summary of paper for the general science reader: *PDF
SUBJECT: DVCS: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : Feynman-like diagrams of the DVCS process ('normal' and 'crossed')
*Colour (eps)

Figure 1b : Feynman-like diagrams of the Bethe-Heitler process (initial and final state radiation)
*Colour (eps)

Figure 2 : Beam helicity asymmetry amplitudes in Deeply Virtual Compton Scattering (DVCS) from a hydrogen target. Shown are the sin\phi and sin2\phi amplitudes of the DVCS-Bethe-Heitler interference term and the sin\phi amplitude of the squared DVCS term in bins of -t, xB, or Q² (1-dimensional representation). Also shown is the integrated value presenting the data in a single bin ('overall'). All 1996-2005 hydrogen data. The bottom row gives for each bin the fraction of the 'associated' process where the proton is excited to a resonant state. The statistical uncertainties are indicated by the error bars, the systematic uncertainies by the error bands. Not included is a 2.8% scale uncertainty due to the measurement of the beam polarization. Also shown are model calculations using the 'VGG' model, or the Dual 'GT' model
*Colour (eps)

Figure 2a : As entry 09-069, but only the panel showing the sin\phi moment of the A_{LU}^Interference
*Colour (eps)

Figure 2b : As entry 09-069, but only the panel showing the sin\phi moment of the A_{LU}^DVCS
*Colour (eps)

Figure 2c : As entry 09-069, but only the panel showing the sin2\phi moment of the A_{LU}^Interference
*Colour (eps)

Figure 3 : Beam helicity asymmetry amplitudes in Deeply Virtual Compton Scattering (DVCS) from a hydrogen target. Shown are the sin\phi and sin2\phi amplitudes of the DVCS-Bethe-Heitler interference term and the sin\phi amplitude of the squared DVCS term in bins of -t for 3 different bins in xB and resulting different average Q² (2-dimensional representation, otherwise as 09-069). The statistical uncertainties are indicated by the error bars, the systematic uncertainies by the error bands. Not included is a 2.8% scale uncertainty due to the measurement of the beam polarization. All 1996-2005 hydrogen data
*Colour (eps)

Figure 4 : Beam charge asymmetry amplitudes in Deeply Virtual Compton Scattering (DVCS) from a hydrogen target. Shown are the cos0\phi, cos\phi, cos2\phi, and cos3\phi amplitudes in bins of -t, xB, or Q² (1-dimensional representation). Also shown is the integrated value presenting the data in a single bin ('overall'). All 1996-2005 hydrogen data. The bottom row gives for each bin the fraction of the 'associated' process where the proton is excited to a resonant state. The statistical uncertainties are indicated by the error bars, the systematic uncertainies by the error bands. Also shown are model calculations using the 'VGG' model, or the Dual 'GT' model
*Colour (eps) *Data

Figure 4a : As entry 09-071, but only the panel showing the constant term (cos0\phi) of A_C
*Colour (eps)

Figure 4b : As entry 09-071, but only the panel showing the cos\phi term of of A_C
*Colour (eps)

Figure 4c : As entry 09-071, but only the panel showing the cos2\phi term of of A_C
*Colour (eps)

Figure 4d : As entry 09-071, but only the panel showing the cos3\phi term of of A_C
*Colour (eps)

Figure 5 : Beam charge asymmetry amplitudes in Deeply Virtual Compton Scattering (DVCS) from a hydrogen target. Shown are the cos0\phi, cos\phi, cos2\phi, and cos3\phi amplitudes in bins of -t for 3 different bins in xB and resulting different average Q² (2-dimensional representation, otherwise as 09-071). The statistical uncertainties are indicated by the error bars, the systematic uncertainies by the error bands. All 1996-2005 hydrogen data
*Colour (eps) *Data

Oct 19, 2009
Observation of the Naive-T-odd Sivers Effect in Deep-Inelastic Scattering
A. Airapetian et al, Phys. Rev. Lett. 103 (2009) 152002 *PDF
Eprint numbers: arXiv:0906.3918 and DESY-09-089
Summary of paper for the general science reader: *PDF
SUBJECT: TRANSVERSE: sivers
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Sivers amplitudes for pions, charged kaons, and the pion-difference asymmetry in bins of x, z, and P_{h,perb}. The systematic uncertainty is given as a band at the bottom of each panel. In addition, there is a 7.3% scale uncertainty from the target-polarization measurement. Full 2002-2005 transverse data set
*BW (eps) *Data

Figure 1 : Same as entry 09-050, but only for pions and in color for presentations
*Colour (eps)

Figure 1 : Same as entry 09-050, but only for kaons and in color for presentations
*Colour (eps)

Figure 1 : Same as entry 09-050, but only for the pion difference asymmetry (+ minus -) and in color for presentations
*Colour (eps)

Figure 2a : Sivers amplitudes for positively charged pions as functions of z or P_{h,perb}, compared for two different ranges in Q². The corresponding fraction of pions stemming from the decay of exclusive vector mesons is provided in the bottom panel (MC)
*Colour (eps) *Data

Figure 2b : As 09-049a, but for positively charged kaons
*Colour (eps)

Figure 3a : Sivers amplitudes for positively charged pions as functions of x. The Q² range for each bin was divided into the two regions above and below the average Q² of each x-bin. In the bottom panel, the average Q² values are given for the two Q² ranges
*Colour (eps) *Data

Figure 3b : As 09-048a, but for positively charged kaons
*Colour (eps)

Figure 4 : Difference of Sivers amplitudes for positively charged pions and positively charged kaons as function of x for all Q², and separated into the high- and low-Q² regions as done for 09-048
*Colour (eps) *BW (eps) *Data

Aug 14, 2009
Exclusive rho⁰ electroproduction on transversely polarized protons
A. Airapetian et al, Phys. Lett. B679 (2009) 100-105 *PDF *PostScript
Eprint numbers: arXiv:0906.5160 (hep-ex) and DESY-09-094
Summary of paper for the general science reader: *PDF
SUBJECT: EXCLUSIVE: rho, sivers
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The lepton scattering and hadron production planes together with the azimuthal angles phi and phi_S
*Colour (eps)

Figure 2 : The polar and azimuthal angles of the decay pi^+ of the Rho0 in the Rho0 rest frame. The positive z-axis is taken opposite to the direction of the residual proton, while the angle phi is defined with respect to the hadron production plane
*Colour (eps)

Figure 3 : The Delta E distributions of the measured yield (number of counts within the acceptance divided by the integrated luminosity) (dots) and a Monte Carlo simulation with Pythia6 of the non-exclusive background normalized to the same integrated luminosity (histogram). The kinematic cuts and the requirements 0.6 GeV < M_pipi < 1.0 GeV and M_KK > 1.04 GeV were applied. The selected exclusive region is indicated by the dashed area
*Colour (eps)

Figure 4 : Values of SDMEs, or combinations thereof, for a transversely polarized proton target and an unpolarized beam. The SDMEs are sorted into three categories, which are separated from each other by the solid horizontal lines. From top to bottom: SDMEs containing s-channel helicity-conserving amplitudes, combinations containing at least one s-channel helicity-changing amplitude, and SDMEs containing two s-channel helicity-changing amplitudes. Within the second category the combinations are sorted into three groups associated with different virtual photon and Rho0 polarizations. The inner error bars represent the statistical uncertainties. The full error bars represent the quadratic sum of the statistical and systematic uncertainties. In addition there is an overall scale uncertainty of 8.1% due to the uncertainty in the target polarization
*Colour (eps) *Data

Figure 5 : The extracted amplitudes of the sin(phi-phi_S) component of A_UT for longitudinally and transversely polarized Rho0 mesons. The inner error bars represent the statistical uncertainties. The full error bars represent the quadratic sum of the statistical and systematic uncertainties. In addition there is an overall scale uncertainty of 8.1% from the uncertainty in the target polarization
*Colour (eps) *Data

Aug 14, 2009
Spin Density Matrix Elements in Exclusive rho⁰ Electroduction on ¹H and ²H Targets at 27.6 GeV Beam Energy
A. Airapetian et al, EPJC 62 (2009) 659-694 *PDF
Eprint numbers: arXiv:0901.0701 (hep-ex) and DESY-08-203
Summary of paper for the general science reader: *PDF
SUBJECT: VECTOR-MESONS: spin transfer, rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Feynman diagram of a generic t-channel exchange process for gamma^* N -> rho⁰ N'
*BW (eps)

Figure 2 : Examples of a) a two-gluon exchange diagram and b) a quark-exchange diagram, shown for the lowest order in the strong coupling constant alpha_s
*BW (eps)

Figure 3 : Definition of angles in the process gamma^* N -> rho⁰ N' -> pi^+ pi^- N'. Here \Phi is the angle between the rho⁰ production plane and the lepton scattering plane in the "hadronic" center-of-mass system of virtual photon and target nucleon. \Theta and \phi are polar and azimuthal angles of the decay \pi^+ in the vector meson rest frame
*BW (eps)

Figure 4 : Two-pion invariant mass distribution in the spectrometer acceptance, fitted with a skewed Breit-Wigner function (solid line). The dotted line represents a constant background contribution
*BW (eps)

Figure 5 : The distribution of rho⁰ mesons in \Delta E, and t' from the 1996-2005 hydrogen data sample in the range 1GeV² < Q² < 7GeV²
*BW (eps)

Figure 6 : Distribution of \Delta E for the 1996-2005 hydrogen data sample shown for four intervals in t' after application of all event selection requirements, except the one for \Delta E. The shaded areas represent the SIDIS background calculated by PYTHIA, normalized to the data in the region 2GeV < \Delta E < 20GeV
*BW (eps)

Figure 7a : Angular distributions with common arbitrary normalization for rho⁰ meson production and decay. Data points represent the positive helicity sample of the proton data. The dotted lines represent isotropic input Monte Carlo distributions as modified by the HERMES acceptance, while the dashed lines are the results of the 23-parameter fit. Here 16 bins are chosen for a more detailed comparison. The data correspond to the full kinematic region of the analysis
*BW (eps)

Figure 7b : As entry 09-023a, but for deuteron data
*BW (eps)

Figure 8 : Shape comparison of the distributions in W, Q², t' and P_{\pi^+}, the momentum of the pi^+ from rho⁰ decay in the laboratory system, for the hydrogen data sample (squares). The shaded areas show rhoMC results using the extracted 23 SDMEs as input for the simulation, normalized to the data. Background has been subtracted from the data
*BW (eps)

Figure 9 : The 23 SDMEs extracted from rho⁰ data: proton (squares) and deuteron (circles) in the entire HERMES kinematics with < x_B>=0.08, < Q²>= 1.95GeV², <-t'>=0.13GeV². The SDMEs are multiplied by prefactors in order to represent the normalized leading contribution of the corresponding amplitude. The inner error bars represent the statistical uncertainties, while the outer ones indicate the statistical and systematic uncertainties added in quadrature. SDMEs measured with unpolarized (polarized) beam are displayed in the unshaded (shaded) areas. The vertical dashed line at zero is indicated for SDMEs expected to be zero under the hypothesis of SCHC
*BW (eps) *Data

Figure 10 : Q² and t' dependences of the "Class A" SDMEs describing the dominant transitions gamma^*_L -> rho⁰_L and gamma^*_T -> rho⁰_T. Filled squares (circles) correspond to proton (deuteron) data. Total uncertainties are depicted, calculated as statistical and systematic uncertainties combined in quadrature. Deuterium data points are presented with a small horizontal offset to improve their visibility
*BW (eps)

Figure 11 : Q² and t' dependences of the "Class B" SDMEs describing the interference of the dominant transitions gamma^*_L -> rho⁰_L and gamma^*_T -> rho⁰_T. Filled squares (circles) correspond to proton (deuteron) data. Total uncertainties are depicted, calculated as statistical and systematic uncertainties combined in quadrature
*BW (eps)

Figure 12 : The Q² dependence of the phase difference \delta between T_{11} and T_{00} amplitudes calculated according to Eq.50 for the proton (filled squares) and deuteron (filled circles) data. The values of \delta, for yields integrated over the range 1GeV² < Q² < 7 GeV², are shown as open symbols. The inner (outer) bars represent the statistical (total) uncertainty
*BW (eps)

Figure 13 : Q² and t' dependence of the "Class C" SDMEs describing the interference of the helicity-flip transition gamma^*_T -> rho⁰_L and one of the dominant helicity-conserving transition. Filled squares (circles) correspond to proton (deuteron) data. Total uncertainties are depicted, calculated as statistical and systematic uncertainties combined in quadrature
*BW (eps)

Figure 14 : Q² and t' dependences of the "Class D" SDMEs describing the interference of the helicity-flip transition gamma^*_L -> rho⁰_T and the dominant transition gamma^*_T -> rho⁰_T. Filled squares (circles) correspond to proton (deuteron) data. Total uncertainties are depicted, calculated as statistical and systematic uncertainties combined in quadrature
*BW (eps)

Figure 15 : Q² and t' dependences of the "Class E" SDMEs describing the interference of the double-helicity-flip transition gamma^*_{-T} -> rho⁰_{T} and the dominant transition gamma^*_T -> rho⁰_T. Filled squares (circles) correspond to proton (deuteron) data. Total uncertainties are depicted, calculated as statistical and systematic uncertainties combined in quadrature
*BW (eps)

Figure 16a : The Q² dependence of u₁ = 1-r_{00}^{04} + 2 r_{1-1}^{04} - 2 r_{11}^{1} - 2 r_{1-1}^{1} for proton (filled squares) and deuteron (filled circles) data. The values of u₁ for yields integrated over the range 1GeV² < Q² < 7GeV² are shown as open symbols. The inner (outer) error bars represent the statistical (total) uncertainties
*BW (eps)

Figure 16b : As entry 09-032a, but t' dependence
*BW (eps)

Figure 17 : Average values of u₁, u₂ and u₃ calculated according to Eqs.52-54 from HERMES proton (filled squares) and deuteron (filled circles). SDMEs are shown together with the values calculated from published SDMEs from DESY, SLAC'79, SLAC'74, ZEUS BPS, ZEUS DIS, and H1. (See publication for references) For HERMES (other experiments) systematic uncertainties are combined in quadrature with (without) accounting for correlations between the SDMEs. The HERMES deuteron and SLAC'74 data points are presented with a small horizontal offset to improve their visibility
*BW (eps)

Figure 18 : Ratios of certain helicity-flip amplitudes to the square root of the sum of all amplitudes squared: \tau_{01}, \tau_{10}, and \tau_{1-1}. HERMES results on proton (filled squares) and deuteron (filled circles) are calculated according to Eqs.59-61, while results from DESY, SLAC'79, SLAC'74, ZEUS BPS, ZEUS DIS and H1 are calculated according to Eqs.70,72. (See publication for references) For HERMES (other experiments) systematic uncertainties are combined in quadrature with (without) accounting for correlations between the SDMEs. The HERMES deuteron and SLAC'74 data points are presented with a small horizontal offset to improve their visibility
*BW (eps)

Figure 19a : Q² dependence of the longitudinal-to-transverse cross section ratio measured at HERMES. Proton results. Filled symbols represent the value of R^{04} calculated from r^{04}_{00} (Eq.69), open symbols correspond to the true value of R calculated according to Eqs.70,72, and crosses (diamonds) represent R^{NPE} Eq.75. Total uncertainties are shown, calculated by combining the statistical and systematic uncertainties in quadrature. The data points for R and R^{NPE} are presented with a small horizontal offset to improve their visibility
*BW (eps)

Figure 19b : As entry 09-035a, but deuteron results
*BW (eps)

Figure 20a : Q² dependence of the longitudinal-to-transverse cross section ratio for exclusive rho⁰ production on the proton. R^{04} calculated from the SDME r^{04}_{00} according to Eq.69. HERMES proton data (filled squares) are compared to measurements of CLAS, Cornell, E665, H1, and ZEUS. The more recent CLAS data (small squares) are from a narrow bin in x_B with approximately the same < x_B > as the HERMES data, which are integrated over the x_B acceptance. (See publication for references)
*BW (eps)

Figure 20b : Q² dependence of the longitudinal-to-transverse cross section ratio for exclusive rho⁰ production on the proton. $R^{04}$ for ZEUS (triangles) and R^{NPE} for HERMES (squares), fitted separately according to Eq.76. For all data points, total uncertainties are shown. Theoretical calculations of R₀ = |T_{00}|^2/|T_{11}|^2 are shown as dashed line at W=5GeV; the uncertainties arising from the uncertainties in the parton distribution functions are shown as a shaded band. (See publication for references)
*BW (eps)

Jan 8, 2009
Measurement of Azimuthal Asymmetries With Respect To Both Beam Charge and Transverse Target Polarization in Exclusive Electroproduction of Real Photons
A. Airapetian et al, JHEP 06 (2008) 066, 24pp *PDF
Eprint numbers: arXiv:0802.2499
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DVCS: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Leading order diagrams for DVCS and Bethe-Heitler processes
*BW (eps)

Figure 2 : Momenta and azimuthal angles for exclusive electroproduction of photons in the target rest frame
*BW (eps)

Figure 3 : Distributions in squared missing-mass from data with positron and electron beams and from Monte Carlo simulations
*Colour (eps)

Figure 4 : Asymmetry amplitudes describing the dependence of the interference term on the beam charge A_C for the exclusive sample
*Colour (eps) *Data

Figure 5 : Asymmetry amplitudes describing the dependence of the squared DVCS amplitudes and the interference term on the transverse target polarization, for the exclusive sample
*Colour (eps) *Data

Figure 6 : Asymmetry amplitudes that are expected to be suppressed
*Colour (eps)

Figure 7 : same as 08-010 (top row) with curves based on dual-parameterisation GPD model. WARNING: this plot is NOT supposed to be shown anymore at conferences. The Dual model is known to have a theoretical theoretical calculation error which makes the interpretation invalid.
*Colour (eps)

Figure 8 : same as 08-011 (top rows) with curves based on calculations using Regge-inspired form of the t-dependence in the dual-parameterisation GPD model. WARNING: this plot is NOT supposed to be shown anymore at conferences. The Dual model is known to have a theoretical theoretical calculation error which makes the interpretation invalid.
*Colour (eps)

Figure 9 : Model-dependent constraint on u-quark total angular momentum J_u vs d-quark total angular momentum J_d. WARNING: this plot is NOT supposed to be shown anymore at conferences. The Dual model is known to have a theoretical theoretical calculation error which makes the interpretation invalid. The remaining models on the plot (VGG) don't describe all Hermes data.
*Colour (eps)

Dec 21, 2008
Measurement of Parton Distributions of Strange Quarks in the Nucleon from Charged-Kaon Production in Deep-Inelastic Scattering on the Deuteron
A. Airapetian et al, Phys. Lett. B 666 (2008) 446 *PDF *PostScript
Eprint numbers: arXiv:0803.2993
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DELTA-Q: delta-s
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The multiplicity corrected to 4pi of charged kaons in seminclusive DIS from a deuterium target, as a function of Bjorken x. The average Q² for each bin are shown in the lower panel
*Colour (eps)

Figure 2 : The strange fragmentation function product obtained from the measured HERMES multiplicity for charged kaons at the average Q² for each bin
*Colour (eps)

Figure 3 : The strange parton distribution from the measured HERMES multiplicity for charged kaons evolved at Q₀²=2.5 GeV²
*Colour (eps) *Data

Figure 4 : Lepton-nucleon polarized cross section asymmetries for inclusive and seminclusive DIS by a deuteron target as a function of Bjorken x, for identified charged kaons
*Colour (eps)

Figure 5 : Non strange and strange quark helicity distributions at Q₀²=2.5 GeV², as a function of Bjorken x. The curves are the LO results from Leader et al. from their analysis of world data
*Colour (eps) *Data

Jun 22, 2008
Evidence for a transverse single-spin asymmetry in leptoproduction of pi⁺ pi^- pairs
A. Airapetian et al, JHEP 06 (2008) 017, 19pp *PDF *PostScript
Eprint numbers: arXiv:0803.2367 and DESY-08-031
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: TRANSVERSE: 2pion
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Depiction of the azimuthal angles
*Colour (eps)

Figure 2 : The top panels show the values of the amplitudes as a function of M_xx, x and z. The bottom panels show the average values of the variables that were integrated over
*Colour *Colour (eps)

Figure 3 : Yield distribution in the invariant mass of the pi+pi^- pairs for the experimental data compared to a PHYTHIA 6 Monte Carlo simulation
*BW (eps)

Figure 4 : The top panels show the values of the amplitudes as a function of M_xx, x and z for Monte Carlo data extracted both in 4pi and experimental acceptance. The bottom panels show the average values of the variables that were integrated over
*Colour (eps)

Jan 6, 2008
Transverse Polarization of Lambda and Lambda-bar Hyperons in Quasi-Real Photon-Nucleon Scattering at HERMES
A. Airapetian et al, Phys. Rev. D76 (2007) 092008, 9pp. *PDF *PostScript
Eprint numbers: arXiv:0704.3133 and DESY-07-036
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: LAMBDA-POL: transverse
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Schematic diagram of inclusive Lambda production and decay
*Colour (eps)

Figure 2 : Invariant mass distributions for Lambda and antiLambda events
*BW (eps)

Figure 3 : Correlation between x_B and the light cone fraction
*BW (eps)

Figure 4 : Ratio of Lambda to Lambdabar yields versus light-cone fraction after background subtraction
*BW (eps) *Data

Figure 5 : Transverse polarization (upper panel) and mean p_T (lower panel)
*BW (eps)

Figure 6a : Transverse polarization as a function of p_T for hyperons for zeta>0.25
*Colour (eps) *BW (eps)

Figure 6b : Transverse polarization as a function of p_T for hyperons for zeta<0.25
*Colour (eps) *BW (eps)

Jul 2, 2007
Cross sections for hard exclusive electroproduction of pi⁺ mesons on a hydrogen target
A. Airapetian et al, Phys. Lett. B 659 (2008) 486-492 *PDF *PostScript
Eprint numbers: arXiv:0707.0222 and DESY-07-098
Summary of paper for the general science reader: *PDF
SUBJECT: EXCLUSIVE: pion
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Leading-order (left panel) and soft-overlap (right panel) diagram for exclusive pi⁺ electroproduction amplitude
*BW (eps)

Figure 2 : Squared missing mass dependence of the normalized-yield difference N_pi+ - N_pi- for data and PHYTHIA Monte Carlo (upper panel) and squared missing mass dependence of the normalized-yield after background subtraction procedure
*Colour (eps) *BW (eps)

Figure 3 : Distributions of exclusive pi⁺ events within the HERMES acceptance as a function of Q², x_B, -t' and phi for data compared with an exclusive Monte Carlo simulation based on a GPD parametrization (Vanderhaegen, Guichon, Guidal)
*BW (eps)

Figure 4 : Differential cross section for exclusive pi⁺ production by virtual photons as a function of -t' for four Q² bins
*Colour (eps) *BW (eps) *Data

Figure 5 : Cross section for exclusive pi⁺ production by virtual photons as a function of Q² for three x_B bins and integrated over t'
*Colour (eps) *Data

Jun 10, 2007
Hadronization in Semi-inclusive deep inelastic scattering on nuclei
A. Airapetian et al, Nucl. Phys. B 780 (2007) 1-27 *PDF *PostScript
Eprint numbers: arXiv:0704.3270 and DESY-07-050
SUBJECT: HADRON-ATTENUATION
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Diagram of the kinematic variables used in the analysis of deep inelastic hadron production from heavy nuclear targets
*BW (eps)

Figure 2 : Multiplicity ratio R_A^h for positively-charged hadrons produced from four heavy targets, as a function of nu, z, and Q²
*Colour (eps) *Data

Figure 3 : Multiplicity ratio R_A^h for negatively-charged hadrons produced from four heavy targets, as a function of nu, z, and Q²
*Colour (eps) *Data

Figure 4 : Multiplicity ratio R_A^h for charged pi, K, and p produced from four heavy targets, as a function of p_t²
*Colour (eps) *Data

Figure 5 : Multiplicity ratio R_A^h for pi⁰ produced from four heavy targets, as a function of nu, z, and Q²
*Colour (eps) *Data

Figure 6 : Multiplicity ratio R_A^h for charged pions (combined) produced from four heavy targets, in z slices as a function of nu, Q², and p_t²
*Colour (eps) *Data

Figure 7 : Multiplicity ratio R_A^h for charged pions (combined) produced from four heavy targets, in nu slices as a function of z, Q², and p_t²
*Colour (eps) *Data

Figure 8 : Multiplicity ratio R_A^h for charged pions (combined) produced from four heavy targets, in p_t² slices as a function of nu, z, and Q²
*Colour (eps) *Data

Figure 9 : Multiplicity ratio R_A^h for charged pions (combined) produced from four heavy targets, in nu slices as a function of L_c
*Colour (eps) *Data

Figure 10 : Alpha parameter obtained from a fit to the A-dependence of charged-pion (combined) production from four heavy targets, in nu slices and as a function of z
*Colour (eps) *Data

Figure 11 : Alpha and Beta parameters obtained from a fit to the A-dependence of charged-pion (combined) production from four heavy targets, as a function of L_c
*Colour (eps) *Data

Figure 12 : Alpha parameter obtained from a fit to the A-dependence of charged pi, K, and p production from four heavy targets, as a function of nu and z
*Colour (eps) *Data

Feb 20, 2007
Beam-Spin Asymmetries in the Azimuthal Distribution of Pion Electroproduction
A. Airapetian et al, Phys. Lett. B 648 (2007) 164-170 *PDF *PostScript
Eprint numbers: hep-ex/0612059 and DESY-06-227
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: AZIMUTHAL: beam
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Definition of kinematic planes for semi-inclusive deep-inelastic scattering
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Jan 21, 2007
Precise determination of the spin structure function g₁ of the proton, deuteron and neutron
A. Airapetian et al, Phys. Rev. D 75 (2007) 012007 *PDF *PostScript
Eprint numbers: hep-ex/0609039 and DESY-06-142
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: G1
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Schematic picture of Deep-Inelastic Scattering for one photon exchange
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Figure 1a : Tar-file including all the Hermes data included in the paper
*Data

Figure 2 : Schematic view of the longitudinally polarized target. From left to right: Atomic Beam Source (ABS) containing Radio-Frequency Transitions (RFT), target chamber with cell and magnet, diagnostic system composed by Target Gas Analyzer (TGA), and Breit-Rabi Polarimeter (BRP)
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Figure 3 : A schematic side view of the HERMES spectrometer
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Figure 4 : Kinematic x-Q² and x-y planes covered by this analysis. The symbols represent the average values of (x,Q²) (top panel) and (x,y) (bottom panel) in each bin. Subdivision of the x-bins along Q² is denoted by different symbols (A, B, C)
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Figure 4a : Kinematic x-y planes covered by this analysis. The symbols represent the average values (x,y) in each bin. Subdivision of the x-bins along Q² is denoted by different symbols (A, B, C)
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Figure 5 : Percentage of charge symmetric background in each $x-Q²$ bin, for the proton and the deuteron targets
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Figure 6 : The distribution of events originating from the arbitrarily selected x-bin shown as a shaded area, from a simulation of QED radiative effects and detector smearing, using a proton target. The vertical lines indicate x-bin boundaries
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Figure 7 : Efficiency for the detection of B-H elastic (el.) and quasi-elastic (q.el.) events in the HERMES spectrometer, for scattering on both deuteron (d) and proton (p). The efficiency is set to unity for x>0.1
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Figure 8 : Correlation matrix in 19 x-bins of g₁ for the proton. The closed symbols represent positive values, while the open ones are for negative values. The area of the symbols represents the size of the correlation
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Figure 8a : same as 06-039 just for deuterium
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Figure 9 : HERMES results on A₁ vs x for proton and deuteron. Error bars represent statistical uncertainties of the data (diagonal elements of the covariance matrix) combined quadratically with those from Monte Carlo statistics. Bands represent systematic uncertainties. Deuteron data points have been slightly shifted in $x$ for visual purposes
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Figure 10 : HERMES results on A₁^p and A₁^d vs x, shown on separate panels, compared to data from SMC, E143, E155, and COMPASS. Error bars represent the sum in quadrature of statistical and systematic uncertainties. For the HERMES data the closed (open) symbols represent values derived by selecting events with Q² >1GeV² (Q² <1GeV²). The HERMES data points shown are statistically correlated by unfolding QED radiative and detector smearing effects; the statistical uncertainties shown are obtained from the diagonal elements of the covariance matrix, only. The E143 and E155 data points are correlated through QED radiative corrections. The lower panel shows the x dependence of < Q² >$ for the different experiments
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Figure 10a : Same as plot 06-041 just without Q²-panel
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Figure 10b : Panel with Q² vs x for the different experiments for plot 06-041
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Figure 11 : HERMES results on g₁^p and g₁^d vs x, shown on separate panels, compared to data from SMC, E143, E155, and COMPASS, in the HERMES x-range. Error bars represent the sum in quadrature of statistical and systematic uncertainties. The HERMES data points shown are statistically correlated by unfolding QED radiative and detector smearing effects; the statistical uncertainties shown are obtained from only the diagonal elements of the covariance matrix. The E143 and E155 data points are correlated through QED radiative corrections. The E155 points have been averaged over their $Q²$ bins for visibility. For the HERMES data the closed (open) symbols represent values derived by selecting events with Q² >1GeV² (Q² <1GeV²)
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Figure 11a : Panel with Q² vs x for the different experiments for plot 06-042
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Figure 12 : HERMES results for xg₁ vs x for the proton and the deuteron. Error bars represent statistical uncertainties of the data (from the diagonal elements of the covariance matrix combined quadratically with those from Monte Carlo statistics. The upper and lower error bands represent the total systematic uncertainties for the proton and deuteron, respectively. The deuteron data points have been slightly shifted in x for visibility. The closed (open) symbols represent values derived by selecting events with Q² >1GeV² (Q² <1GeV²)
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Figure 12a : same plot as 06-043 with Q²-panel for the HERMES-points
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Figure 13 : HERMES results on xg₁^p and xg₁^d vs x, shown on separate panels, compared to data from SMC, E143, E155, and COMPASS. The error bars represent the sum in quadrature of statistical and systematic uncertainties. The HERMES data points shown are statistically correlated by unfolding QED radiative and detector smearing effects; the statistical uncertainties shown are obtained from only the diagonal elements of the covariance matrix. The E143 and E155 data points are correlated due to the method for correcting for QED radiation. For the HERMES data the closed (open) symbols represent values derived by selecting events with Q²>1GeV² (Q² <1GeV² )
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Figure 13a : Same plot as 06-044 just without Q² pannel and the COMPASS data are from hep-ex/0609038 and not from hep-ex/0501073 like in the bw-paper plots
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Figure 13b : Q²-panel plot for 06-044a
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Figure 14 : Top panel: the structure function g₁ⁿ obtained from g₁^p and g₁^d, compared with similar data from SMC, E143, and E155 in the HERMES x-range. Second panel from the top: g₁ⁿ as obtained from a He³ target by JLab, HERMES, E142, and E154. Total error bars are shown, obtained by combining statistical and systematic uncertainties in quadrature. The bottom panel shows the < Q² >$ of each data point in the top two panels. E155 data have been averaged over their Q² bins for visibility. For the HERMES data the closed (open) symbols represent values derived by selecting events with $Q² >1$~GeV$^2$ ($ Q² <1$~GeV$^2$)
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Figure 14a : Same as 06-045 just xg₁ⁿ
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Figure 15 : Top panel: xg₁ⁿ from data for g₁^p and g₁^d. Bottom panel: the x-weighted non-singlet spin structure function xg₁^{NS}, compared to data from SMC, E143, and E155. All data are presented at their measured values of < Q² >$, except that the E155 data in each x bin have been averaged over Q² for visual purposes. Total uncertainties are shown as bars. For the HERMES data the closed (open) symbols represent values derived by selecting events with Q² >1GeV² (Q²<1GeV²)
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Figure 15a : Same as 06-046 just with including a panel for Q² vs x for the different experiments
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Figure 16 : Integrals of g₁^{p,d,n,NS} over the range 0.021=2=5GeV². Inner error bars represent total uncertainties excluding the normalization systematic uncertainty from beam and target; outer error bars include the contribution coming from the $Q²$ evolution. Three of the four sets of points are slightly shifted in $x$ for visibility
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Figure 17a : Migration matrices $M_{\spar}$ (the $M_{\sant}$ matrices look similar) for two different binnings. Migration matrix for a pure x binning. The horizontal and vertical lines divide the x-bins; within each x-bin the Q²-bins are arranged in increasing Q². The matrices are extracted from a fully reconstructed Monte Carlo data set simulating both QED radiative and detector effects for inclusive DIS on a proton target
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Figure 17b : Migration matrices $M_{\spar}$ (the $M_{\sant}$ matrices look similar) for two different binnings. Migration matrix for the combined x and Q² binning used in this analysis. The horizontal and vertical lines divide the x-bins; within each x-bin the Q²-bins are arranged in increasing Q². The matrices are extracted from a fully reconstructed Monte Carlo data set simulating both QED radiative and detector effects for inclusive DIS on a proton target
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Figure 18 : Top two panels: measured and unfolded Born asymmetries for proton and deuteron. The error bars of the Born asymmetries are the square root of the diagonal elements of the covariance matrix obtained after unfolding, with the inclusion of the uncertainty due to the statistics of the Monte Carlo. Bottom panel: uncertainty inflation when going from measured to Born asymmetry due to the unfolding procedure. The symbols A, B and C refer to the Q²-bins
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Dec 22, 2006
The Beam-Charge Azimuthal Asymmetry and Deeply Virtual Compton Scattering
A. Airapetian et al, Phys. Rev. D 75 (2007) 011103(R), 5pp. *PDF *PostScript
Eprint numbers: hep-ex/0605108 and DESY-06-078
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DVCS: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Distributions in missing--mass squared from data (statistical error bars) and from Monte Carlo simulations (line). The latter include elastic BH (filled area) and associated BH (hatched area) processes as well as semi--inclusive background. The vertical lines enclose the selected exclusive region
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Figure 2 : Beam--charge asymmetry $A_C$ for the hard electroproduction of photons off protons as a function of the azimuthal angle \phi, for the exclusive sample (-1.5GeV < M_X < 1.7GeV) before background correction. Statistical uncertainties are shown. The solid curve shows the result of a four--parameter fit: (-0.011\pm0.019) + (0.060\pm0.027) \cos \phi + (0.016\pm0.026) \cos 2 \phi + (0.034\pm0.027) \cos 3 \phi. The dashed line shows the pure \cos \phi dependence
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Figure 3 : function of the missing mass. Statistical uncertainties are shown
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Figure 4 : The $cos \phi$ amplitude of the beam--charge asymmetry as a function of $-t$ for the exclusive region (-1.5GeV < M_X < 1.7GeV), after background correction. The error bars (band) represent(s) the statistical (systematic) uncertainties. The calculations based on GPD models (VGG, PRD 60 (1999) 094017, Goeke et al. Prog. Part. Nucl. Phys. 47 (2001) 401) use either a factorized t--dependence with (dashed--dotted) or without (dotted) the D-term contribution, or a Regge--inspired t--dependence with (dashed) or without (solid) the D-term contribution
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Oct 31, 2006
Longitudinal Spin Transfer to the Lambda Hyperon in Semi-Inclusive Deep-Inelastic Scattering
A. Airapetian et al, Phys. Rev. D 74 (2006) 072004, 11 pp. *PDF *PostScript
Eprint numbers: hep-ex/0607004 and DESY-06-100
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: LAMBDA-POL: longitudinal
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The single-quark scattering mechanism leading to Lambda- production in polarized deep-inelastic positron scattering
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Figure 2 : Purities for \lam production from the proton target within the HERMES acceptance, calculated separately for quarks and antiquarks of various flavors at x_F>0 with < Q² > $=2.41 GeV²
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Figure 3 : The yield of semi-inclusively produced \lam hyperons in deep-inelastic scattering. The left (right) panel shows the invariant-mass spectrum before (after) the application of background suppression cuts. The vertical lines show the boundaries at \pm 3.3\sigma. The spectra include essentially all data recorded from unpolarized targets by the HERMES spectrometer in the years 1996 -- 1997 and 1999 -- 2000, corresponding to a yield of 30.3 \times 10⁶ inclusive deep-inelastic scattering events
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Figure 4 : Dependence of the longitudinal spin-transfer coefficient on z, for x_F > 0. The curves represent the phenomenological model calculations as described in the text. Error bars are statistical only
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Figure 5 : Dependence of the longitudinal spin-transfer coefficient on x_F. The HERMES measurements are represented by the solid circles, while the open symbols represent data from NOMAD (squares) and E665 (circles). Error bars are statistical only. As explained in the text, for the neutrino-induced NOMAD data the quantity plotted is $-P^\nu_\Lambda$
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Apr 26, 2006
Double-hadron Leptoproduction in the Nuclear Medium
A. Airapetian et al, Phys. Rev. Lett. 96 (2006) 162301, 5pp. *PDF *PostScript
Eprint numbers: hep-ex/0510030 and DESY-05-205
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: HADRON-ATTENUATION
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The ratio $R_{2h}$ as a function of z₂ for N¹⁴ (squares), Kr (circles) and Xe (triangles) with z₁>0.5. The systematical uncertainty is 2\% for all the targets and is independent of z₂. In the upper panel the curves (solid for N¹⁴, dashed for Kr, dotted for Xe) are calculated within a BUU transport model by Falter et al. In the bottom panel the same data are shown with calculations that assume only absorption for the three nuclei (same line types as in the upper plot)
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Figure 2 : The ratio $R_{2h}$ as a function of z₂ for N¹⁴ (squares), Kr (circles) and Xe (triangles) with z₁>0.5 for Selection II. The systematic uncertainty is 4\% (3\%) for xenon and krypton (nitrogen) and is independent of z₂. The curves N¹⁴: solid; Kr: dashed; Xe: dotted) are from the models by X.N.Wang and A.Majumder
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Dec 18, 2005
Measurement of the Tensor Structure Function b₁ of the Deuteron
A. Airapetian et al, Phys. Rev. Lett. 95 (2005) 242001, 6pp. *PDF *PostScript
Eprint numbers: hep-ex/0506018 and DESY-05-077
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: B1
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The tensor asymmetry $\At(x)$. The error bars are statistical and the shaded band shows the systematic uncertainty
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Figure 1a : Korrelation matrix for the born level asymmetries on the deuteron
*Data

Figure 2 : The tensor structure function presented as (top) $\bd(x)$ and (middle) $x\bd(x)$. The error bars are statistical and the shaded bands show the systematic uncertainty. The bottom panel shows the average value of $Q²$ in each $x$-bin
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Aug 24, 2005
Subleading-twist Effects in Single-spin Asymmetries in Semi-inclusive Deep-inelastic Scattering on a Longitudinally Polarized Hydrogen Target
A. Airapetian et al, Physics Letters B 622 (2005) 14-22 *PDF *PostScript
Eprint numbers: hep-ex/0505042 and DESY-05-072
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: AZIMUTHAL: pi-proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The definitions of the azimuthal angle $\phi$ of the hadron production plane, relative to the plane containing the momentum $\vec{l}$ ($\vec{l}'$) of the incident (scattered) lepton
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Figure 2 : The various azimuthal moments appearing in the measurement of the $\sin\phi$ modulations of single-spin asymmetries on a longitudinally polarised target. Open symbols: measured epton axis moments; the ones from a transversely polarised target are multiplied by $-\sin\theta_{gamma ^*}$. Closed symbols: subleading-twist contribution to the measured lepton-axis asymmetries on a longitudinally polarised target. An overall systematic error of 0.003 is not included in the figure
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May 20, 2005
The HERMES Polarized Hydrogen and Deuterium Gas Target in the HERA Electron Storage Ring
A. Airapetian et al, Nucl. Instr. and Meth. A540 (2005) 68 *PDF *PostScript
Eprint numbers: physics/0408137 and DESY-04-128
SUBJECT: EXPERIMENT: target
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Schematic view of the HERMES longitudinally polarized target. From left to right: Atomic Beam Source (ABS), target chamber with cell and magnet, and diagnostic system composed by Target Gas Analyzer (TGA) and Breit-Rabi Polarimeter (BRP). The locations of the radio-frequency transition (RFT) units are indicated
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Figure 2 : Longitudinal target chamber and superconducting magnet viewed from downstream with respect to the HERA beam direction (left), and from above (right)
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Figure 3a : Field strength of the longitudinal target magnet measured along the HERA beam direction {\it{z}}, covering the full length of the storage cell. The line shows a polynomial fit to the measurement
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Figure 3b : Transverse magnet field uniformity measured along the {\it{z}} axis at the nominal field strength B=297 mT. Deviations of \Delta B_y=0.15 mT (vert.) and \Delta B_x=0.60 mT (horiz.) have been measured within the cell volume
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Figure 4 : The storage cell and its support flange
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Figure 5 : Schematic view (from downstream of the electron beam) of the HERMES ABS with dissociator and collimator for beam formation. Two sets of sextupole magnets are located along the beam axis as are the high-frequency transitions. The axis of the ABS is tilted by $30^\circ$ downwards with respect to the horizontal plane
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Figure 6 : Hyperfine energy levels of hydrogen (left) and deuterium (right) atoms as a function of the magnetic holding field (Breit-Rabi diagram) and corresponding labeling. The field values are scaled with the corresponding critical field and energy values with the corresponding hyperfine energy
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Figure 7 : A schematic diagram of the Target Gas Analyzer. The gas of atoms and molecules diffuses through the extension tube and is collimated by two baffles before entering the ionizing volume. The chopper is used for background subtraction
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Figure 8 : Schematic view of the BRP/TGA vacuum system
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Figure 9 : Time spectrum of atomic count rates in the TGA. The vertical lines indicate the binning used to define the chopper positions open, undefined and closed
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Figure 10 : Schematic layout of the BRP. The rf-transition units extend from z = 600 to 810 mm. The beam blocker at the entrance to the first 6-pole magnet ensures 100% rejection of atoms with $m_s=-\frac{1}{2}$. The beam shutter is used to measure the hydrogen contribution coming from dissociative water ionization
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Figure 11 : Measured fractional hyperfine populations vs. magnetic field for hydrogen for the various injection modes. The measured values are given by symbols, while the lines show a fit using the solutions of equation 28
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Figure 12 : Possible beam-induced nuclear depolarizing resonances in the HERMES target. The frequency difference between pairs of hyperfine states whose transitions lead to nuclear depolarization are plotted as a function of the holding field. The frequency values are normalized to $\nu_{HERA}=10.42\,$MHz. The symbols representing the resonance conditions are clearly distinguishable for the $\pi$ transitions, while they overlap with each other in the case of $\sigma$ and $\pi\ket{3}\leftrightarrow\ket{6}$ transitions, which are separated by a difference in the intensity of the holding field $\Delta B_T$ of only 0.37\,mT. The dashed lines represent the working fields of the transversely (left) and longitudinally (right) polarized targets
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Figure 13 : Simulated correlation between the values measured by the TGA or BRP detectors and their corresponding density-weighted average values in the storage cell. The three solid curves represent the three scenarios for the state of the cell surface: homogeneous cell (HC), homogeneous beam tube (HBT), and inhomogeneous beam tube (IBT). The left figure shows the range for recombination and the right picture shows the range for wall depolarization. Acceptable uncertainties of $\alpha_r$ and $\depol_{WD}$ (differences among the three horizontal dotted lines) can be achieved only with $\alpha_r^{TGA}$ and $\depol_{WD}^{BRP}$ close to unity (vertical dotted lines). The corresponding uncertainty grows rapidly with increasing recombination or depolarization
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Figure 14a : The TGA measurements for the entire 1997 data taking period. The vertical dashed lines indicate HERA beam loss events which affected the cell surface properties, and the solid line indicates the replacement of the target cell
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Figure 14b : The TGA measurements for the entire 1997 data taking period. The vertical dashed lines indicate HERA beam loss events which affected the cell surface properties, and the solid line indicates the replacement of the target cell
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Figure 15a : Atomic fraction, $\alpha^{TGA}$ measured by TGA during the year 2000 running period. Each symbol represents data averaged over a 72-hour bin. The absolute bin averaged values are always above 0.9
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Figure 15b : Vector/tensor polarization, $P^{BRP}$, measured by BRP during the year 2000 running period. Each symbol represents data averaged over a 72-hour bin. The tensor polarization (lower plot) was employed from July on
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Figure 16 : Nuclear vector polarization $P_z^{BRP}$ as function of the cell temperature T measured in August 2000. No dependence on the temperature is observed. The operating temperature of the target during data collection was ⁶⁰K
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Figure 17a : Measured atomic fraction as a function of the cell temperature for $T_{cell}<100\,$K for the deuterium running in 2000. No dependence on the temperature can be seen. The working temperature during normal operation was set to $T_{cell}=60\,$K
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Figure 17b : A temperature scan with hydrogen taken in 1997
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Figure 18a : The TGA measurements for the 2002/03 data taking period
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Figure 18b : The BRP measurements for the 2002/03 data taking period
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Mar 28, 2005
Single-Spin Asymmetries in Semi-Inclusive Deep-Inelastic Scattering on a Transversely Polarized Hydrogen Target
A. Airapetian et al, Phys. Rev. Lett. 94 (2005) 012002 *PDF *PostScript
Eprint numbers: hep-ex/0408013 and DESY-04-141
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: TRANSVERSE
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The definitions of the azimuthal angles of the hadron production plane and the axis of the relevant component $\vec{S}_\perp$ of the target spin, relative to the plane containing the momentum $\vec{k}$ ($\vec{k}'$) of the incident (scattered) lepton
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Figure 2a : Virtual-photon Collins moments for charged pions as as a function of $x$ and $z$, multiplied by two to have the possible range $\pm1$. The error bars represent the statistical uncertainties. Common 8\% scale uncertainty in the moments. X-Axis included, contrary to plot 05-062
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Figure 2b : Virtual-photon Sivers moments for charged pions as as a function of $x$ and $z$, multiplied by two to have the possible range $\pm1$. The error bars represent the statistical uncertainties. Common 8\% scale uncertainty in the moments. X-Axis included, contrary to plot 05-064
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Figure 2c : The plot shows the relative contributions to the data from simulated exclusive vector meson production
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Feb 26, 2005
Search for an Exotic S=-2, Q=-2 Baryon Resonance at a Mass near 1862 MeV in Quasireal Photoproduction
A. Airapetian et al, Phys. Rev. D 71 (2005) 032004 *PDF *PostScript
Eprint numbers: hep-ex/0412027 and DESY-04-239
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: EXOTICS: pentaquark
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : Invariant mass distribution of the p pi^-pi^- system and charge conjugated (c.c.) mode
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Figure 1b : Invariant mass distribution of the p pi^- system and charge conjugated (c.c.) mode
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Figure 2 : Invariant mass distribution of the p pi^- pi^- pi^- system, subject to the constraints in event topology discussed in the text. The mixed-event background is represented by the gray shaded histogram, which is normalized to the background component of the fitted curve described in the text. The arrow shows the hypothetical \Xi^{--}_{3/2} mass
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Figure 3 : Invariant mass distribution of the p\pi^-\pi^-\pi^+$(plus c.c.) system, subject to the constraints in event topology discussed in the text. The mixed-event background is represented by the gray shaded histogram, which is normalized to the background component of the fitted curve described in the text. The arrow shows the hypothetical \Xi^{0}_{3/2} mass. The excess near 1.77GeV has a statistical significance of only 1.8 \sigma
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Jan 31, 2005
Quark Helicity Distributions in the Nucleon for up, down, and strange Quarks from Semi-inclusive Deep-inelastic Scattering
A. Airapetian et al, Phys. Rev D 71 (2005) 012003 *PDF *PostScript
Eprint numbers: hep-ex/0407032 and DESY-04-107
SUBJECT: DELTA-Q
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Diagram of the deep-inelastic scattering process. The incoming lepton emits a virtual photon which is absorbed by one of the quarks in the nucleon. In the case depicted, the struck quark fragments into a pion in the final state. In semi--inclusive processes, the scattered lepton and part of the hadronic final state are detected in coincidence
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Figure 2 : Schematic diagram of the HERA accelerator layout until 2000 with the location of the four experiments. Also shown are the locations of the spin--rotators and the two polarimeters
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Figure 3 : Diagram of the HERMES polarized target. Shown are the atomic beam source (ABS), the target gas analyzer (TGA) and the Breit--Rabi polarimeter (BRP). SFT, MFT, and WFT label the strong, medium, and weak field transitions in the ABS and the BRP
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Figure 4 : Side view of the HERMES spectrometer. The positron beam enters from the left. The spectrometer is split into two halves, one above the beam and one below, by a flux exclusion plate to protect the beams from the magnetic field. See the text for further details on the detectors
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Figure 5 : Typical PID detector responses. The distributions are based on a small set of the data collected in 2000, except for the threshold \v{C}erenkov response, which was computed from a data set of similar size collected in 1997. The truncated mean is shown in the case of the TRD. The relative size of the lepton (dashed line) and hadron distributions (solid line) was scaled to the flux ratio in the respective data--taking periods to give a better idea of the level of contamination possible from each detector. The flux ratio of electrons to hadrons is typically $\sim 10\,\%$ for these data
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Figure 6 : Tracking system resolution for lepton and hadron tracks for the detector configuration used since 1998. In the left panel the relative momentum resolution is displayed, and the right panel shows the resolution in the horizontal scattering angle $\theta_x$, both as a function of the track momentum $p$
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Figure 7 : Two--dimensional distribution of PID values for all particles in the acceptance. The quantities $\mathrm{PID3}$ and $\mathrm{PID5}$ are defined as $\mathrm{PID3}\equiv\mathrm{PID}_{cal}+\mathrm{PID}_{pre} +\mathrm{PID}_{ric}$ and $\mathrm{PID5}\equiv\mathrm{PID}_{trd}
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Figure 8 : The distribution of the total $\mathrm{PID}$ value. This logarithmic ratio of probabilities includes the particle fluxes and the responses of all PID detectors. The left hand peak is the hadron peak, while the right hand peak originates from leptons. The limits that were applied in the analysis are shown as vertical lines
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Figure 9 : Identification efficiency and hadron contamination of the DIS lepton sample as a function of $x$. Because correlations between the responses of the PID detectors were neglected, the contaminations are uncertain by a factor of two. The deuteron data have slightly worse efficiencies and contaminations because of the better hadron--lepton discrimination of the threshold \v{C}erenkov counter compared to the RICH
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Figure 10 : Cerenkov angles associated with the three particle hypotheses as a function of the particle momentum. The characteristic angles of \v{C}erenkov light emitted in the aerogel ($n=1.03$) are given by the solid lines. The characteristic angles for emission in the gas ($n=1.0014$) are shown as the dashed lines. The corresponding histogram entries are experimentally determined angles of a sample of SIDIS hadrons
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Figure 11 : The observed asymmetries $A_\|$ and $A_\|^{\pi^+}$ on the proton target compared with the corresponding Born asymmetries. The Born asymmetries are offset horizontally for better presentation. See the text for details
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Figure 12 : Uncertainty inflation caused by detector smearing and QED radiative effects. The left hand panel shows the uncertainty inflation of the inclusive asymmetry for the proton and the right hand panel that of the positive pion asymmetry. In both panels the open triangles present the uncertainty inflation caused by detector effects, the open squares present the inflation caused by QED radiative effects, and the filled circles show the total uncertainty inflation
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Figure 13 : The inclusive and semi--inclusive Born level asymmetries on the proton, corrected for instrumental smearing and QED radiative effects. The error bars give the statistical uncertainties, and the shaded bands indicate the systematic uncertainty. The open squares show the positive and negative hadron asymmetries measured by the SMC collaboration, limited to the HERMES $x$--range
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Figure 13a : Korrelation matrix for the born level asymmetries on the proton
*Data

Figure 14 : The inclusive and semi--inclusive Born level asymmetries on the deuteron. One data point at $x = 0.45$ for the $K^-$ asymmetry including its large error bar is outside the displayed range; all data points are listed in XIII
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Figure 14a : Korrelation matrix for the born level asymmetries on the deuteron
*Data

Figure 15 : The semi--inclusive Born asymmetries for positive and negative pion production on the proton as a function of $z$. The error bars indicate the statistical uncertainties and the error band represents the systematic uncertainties. The solid line is the z dependence from the Monte Carlo simulation of the asymmetries
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Figure 16 : Born level Monte Carlo asymmetries on the proton in the experimental acceptance and in $4\pi$. The left hand plot compares the semi--inclusive asymmetries $A_{1,p}^{\pi^+}$ and the right hand plot the semi--inclusive asymmetries $A_{1,p}^{\pi^-}$. The asymmetries in the experimental acceptance also include the hadron momentum cut. For display purposes the full data points have been offset horizontally. The lower panels present the same data in the form of the difference in the asymmetries divided by the total experimental uncertainty $\sigma_{born}$ in the corresponding measured Born asymmetry
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Figure 17 : Multiplicities of charged pions and kaons in the HERMES acceptance compared with Monte Carlo data as function of $z$. Statistical uncertainties in the data are too small to be visible. The multiplicities shown were not corrected for radiative and instrumental effects
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Figure 18 : Purities for positive and negative pions and kaons on a proton and a free neutron target. Each column corresponds to scattering off a certain quark flavor. The shaded bands indicate the estimated systematic uncertainties due to the fragmentation parameters. The estimate derives from a comparison of two parameter sets
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Figure 19 : The quark polarizations in the 5 parameter $\times$ 9 $x$--bins fit. The polarizations, shown as a function of $x$, were computed from the HERMES inclusive and semi--inclusive asymmetries. The error bars are the statistical uncertainties. The band represents the total systematic uncertainty, where the light gray area is the systematic error due to the uncertainties on the fragmentation model, and the dark gray area is from the contribution of the Born asymmetries
*Colour (eps) *BW (eps) *Data

Figure 20 : The quark helicity distributions $x\,\Delta q(x,Q₀²)$ evaluated at a common value of $Q²₀=2.5\,\GeV²$ as a function of $x$. The dashed line is the GRSV2000 parameterization (LO, valence scenario) scaled with $1/(1+R)$ and the dashed--dotted line is the Bl\"umlein--B\"ottcher (BB) parameterization (LO, scenario 1)
*Colour (eps) *BW (eps) *Data

Figure 21 : The flavor asymmetry in the helicity densities of the light sea evaluated at $Q₀²=2.5\,\GeV²$. The data are compared with predictions in the $\chi$QSM and a meson cloud model \cite{Cao:2003}. The solid line with the surrounding shaded band show the $\chi$QSM prediction together with its $\pm 1\,\sigma$ uncertainties while the dash--dotted line shows the prediction in the meson cloud model. The uncertainties in the data are presented as in Fig. 19
*Colour (eps) *BW (eps) *Data

Figure 22 : The semi--inclusive Born level asymmetry $A_{1,d}^{K^+ + K^-}$ for the total charged kaon flux on a deuterium target, corrected for instrumental smearing and QED radiative effects. The uncertainties are presented analogously to Fig. 13
*Colour (eps) *BW (eps) *Data

Figure 23 : The average strange quark helicity density $x\cdot[\Delta s(x)+\Delta\bar{s}(x)]/2$ from the isoscalar extraction method (full points). For comparison the open symbols denote the results from a five parameter fit (see text), which are offset horizontally for presentation. The band in the bottom part gives the total systematic uncertainty on the results from the isoscalar extraction. The dark shaded area corresponds to the uncertainty from the input asymmetries, and the open part relates to the uncertainty in $\lambda_s$
*Colour (eps) *BW (eps) *Data

Figure 24 : Matrices $n_u(i,j)=n_\spar(i,j)+n_\sant(i,j)$ for DIS events and SIDIS $\pi^+$ events on the proton. The binning shown corresponds to the 9 bins in $x$ that were used in the asymmetry and $\Delta q$ analysis
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Aug 30, 2004
Hard Exclusive Electroproduction of pi⁺ pi^- Pairs
A. Airapetian et al, Physics Letters B 599 (2004) 212 *PDF *PostScript
Eprint numbers: hep-ex/0406052 and DESY-04-097
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: EXCLUSIVE: 2pion
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : for explanation see 04-071d
*Colour (eps) *BW (eps)

Figure 1b : for explanation see 04-071d
*Colour (eps) *BW (eps)

Figure 1c : for explanation see 04-071d
*Colour (eps) *BW (eps)

Figure 1d : Leading twist diagrams for the hard exclusive reaction e^+ T ---> e^+ T' pi^+ pi^-$. Gluon exchange (a) gives rise to pions in the isovector state only, while the quark exchange mechanism (b,c,d) gives rise to pions in both isoscalar and isovector states
*Colour (eps) *BW (eps)

Figure 2a : Distribution of pi^+pi^- events versus $\Delta E$ for hydrogen with 0.60 < m_{pipi} < 0.95 GeV}. The data are represented by the solid circles, while the simulated (SIDIS) background is represented by the histogram. The Monte Carlo results are normalized to the data using the region of the spectrum above \Delta E>2 GeV
*Colour (eps) *BW (eps)

Figure 2b : Yield of the exclusive events as obtained by subtracting the normalized Monte Carlo events from the data. The result (thin line) of an arbitrarily normalized Monte Carlo simulation using the diffractive \rho⁰ DIPSI generator is superimposed on the exclusive distribution
*Colour (eps) *BW (eps)

Figure 3a : Invariant mass spectrum for hydrogen for \Delta E<0.625 GeV (solid points) and \Delta E<0.125 GeV} (shaded area). For the spectrum the requirement x>0.1 has been applied. The m_{\pi\pi}-spectrum} for \Delta E<0.125 GeV is normalized and superimposed (shaded area) to show the suppression of the \omega ---> \pi^+\pi^-\pi⁰ contamination
*Colour (eps) *BW (eps)

Figure 3b : Invariant mass spectrum for deuterium for \Delta E<0.625 GeV (solid points) and \Delta E<0.125 GeV} (shaded area). For the spectrum the requirement x>0.1 has been applied. The m_{\pi\pi}-spectrum} for \Delta E<0.125 GeV is normalized and superimposed (shaded area) to show the suppression of the \omega ---> \pi^+\pi^-\pi⁰ contamination
*Colour (eps) *BW (eps)

Figure 4a : for explanation see 04-074d
*Colour (eps) *BW (eps) *Data

Figure 4b : for explanation see 04-074d
*Colour (eps) *BW (eps)

Figure 4c : for explanation see 04-074d
*Colour (eps) *BW (eps)

Figure 4d : The m_{\pi\pi}-dependence of the Legendre moments \la P₁ \ra (04-074a/b) and \la P₃ \ra (04-074c/d) for hydrogen (04-074a/c) and deuterium (04-074b/d), for x>0.1. The region 0.80(980) resonance, as shown in the insert. In 04-074a/b, leading twist predictions for the hydrogen target including the two-gluon exchange mechanism contribution, at x=0.16 are shown. A calculation without the gluon exchange contribution is shown for limited m_{\pi\pi} values, (open squares at x=0.1, open triangles at x=0.2). In these calculations, the contribution from f₀ meson decay was not considered. Instead, the inset panel for the hydrogen target shows a prediction, which includes the f₀ meson contribution. All experimental data have \la x \ra =0.16, \la Q² \ra = 3.2 (3.3) GeV², and \la -t \ra = 0.43 (0.29) GeV²} for hydrogen (deuterium). The systematic uncertainty is represented by the error band
*Colour (eps) *BW (eps)

Figure 5a : for explanation see 04-075d
*Colour (eps) *BW (eps)

Figure 5b : for explanation see 04-075d
*Colour (eps) *BW (eps)

Figure 5c : for explanation see 04-075d
*Colour (eps) *BW (eps)

Figure 5d : The m_{\pi\pi}-dependence} of \la P₁ + 7/3 \cdot P₃ \ra (04-075a/b) and \la P₁ - 14/9 \cdot P₃ \ra (04-075c/d) for hydrogen (04-075a/c) and deuterium (04-075b/d). The data have \la x \ra =0.16, \la Q² \ra = 3.2 (3.3) GeV²}, and \la -t \ra = 0.43 (0.29) GeV² for hydrogen (deuterium). The systematic uncertainty is represented by the error band
*Colour (eps) *BW (eps)

Figure 6a : for explanation see 04-076b
*Colour (eps) *BW (eps)

Figure 6b : The x-dependence of the Legendre moments< P₁ > for both targets separately, in the regions 0.30 *Colour (eps) *BW (eps)

Apr 22, 2004
Nuclear Polarization of Molecular Hydrogen Recombined on a Non-metallic Surface
A. Airapetian et al, Eur. Phys. J D 29 (2004) 21 *PDF *PostScript
Eprint numbers: physics/0408138 and DESY-03-168
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: EXPERIMENT: target
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : A schematic layout of the HERMES hydrogen target. From left to right: injection tube for atomic beam source (ABS), target chamber with cell and magnet, sample tube taking gas to target gas analyzer (TGA) and Breit-Rabi polarimeter (BRP)
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Figure 2 : Summary of the existing measurements of the nuclear polarization of recombined molecules. The newly obtained HERMES measurement at 260 K with a holding field of 330 mT is compared to the measurement by AmPS and IUCF obtained at room temperature and magnetic holding fields of 28 mT and 440 mT respectively
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Mar 8, 2004
Evidence for a Narrow |S|=1 Baryon State at a Mass of 1528 MeV in Quasi-real Photoproduction
A. Airapetian et al, Physics Letters B 585 (2004) 213 *PDF *PostScript
Eprint numbers: hep-ex/0312044 and DESY-03-213
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: EXOTICS: pentaquark
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Invariant mass distribution of two oppositely charged pions. A window corresponding to \pm 2 \sigma is shown by the vertical lines
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Figure 2 : Distribution in invariant mass of the $p \pi^+\pi^-$ system. The experimental data are represented by the filled circles with statistical error bars, while the fitted smooth curves result in the indicated position and \sigma width of the peak of interest. In panel a), the PYTHIA-6 Monte Carlo simulation is represented by the gray shaded histogram, the mixed-event model normalised to the PYTHIA-6 simulation is represented by the fine-binned histogram, and the fitted curve is described in the text. In panel b), a fit to the data of a Gaussian plus a third-order polynomial is shown
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Figure 3 : Spectra of invariant mass $M_{pK^-}$ (top) and M_{pK^+} (bottom). A clear peak is seen for the \Lambda(1520) in the M_{pK^-} invariant mass distribution. However, no peak structure is seen for the hypothetical \Theta^{++} in the M_{pK^+} invariant mass distribution near 1.53GeV
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Figure 4 : Mass values and experimental FWHM widths observed in various experiments for the $\Theta^+$ state. The inner error bars represent the statistical uncertainties, and the outer error bars represent the quadratic sum of the statistical and systematic uncertainties. (Some uncertainties for the widths are not available from the other experiments.) The hatched area corresponds to the weighted average of all data \pm1 standard deviation
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Jan 30, 2004
Evidence for Quark-Hadron Duality in the Proton Spin Asymmetry A₁
A. Airapetian et al, Phys. Rev. Lett. 90 (2003) 092002 *PDF *PostScript
Eprint numbers: hep-ex/0209018 and DESY-02-137
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: G1: duality
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : A₁ vs x for both the resonance and DIS regions, demonstrating that quark-hadron duality holds in the spin sector
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Jan 25, 2004
Flavor Decomposition of the Sea Quark Helicity Distributions in the Nucleon from Semi-inclusive Deep-inelastic Scattering
A. Airapetian et al, Phys. Rev. Lett. 92 (2004) 012005 *PDF *PostScript
Eprint numbers: hep-ex/0307064 and DESY 03-067
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DELTA-Q
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Virtual photo-absorption asymmetries A^h₁ for semi-inclusive DIS on the deuterium target as a function of Bjorken x, for identified charged pions (compared to all charged hadrons from SMC in the x-range of the present experiment), and for identified charged kaons. The error bars are statistical, and the bands at the bottom represent the systematic uncertainties. Two data points for K^- at large x are off-scale with large error bars
*Colour (eps) *BW (eps) *Data

Figure 2 : Quark helicity distributions at Q²=2.5 GeV², as a function of Bjorken x, compared to two LO QCD fits to previously published inclusive data shown as dashed GRSV-2000 (standard scenario) and dot-dashed BB (scenario~1) curves. The error bars are statistical and the bands at the bottom represent the systematic uncertainties, where the light area is the contribution due to the uncertainties of the fragmentation model, and the dark area is the contribution due to those of the asymmetries
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Figure 3 : The light quark sea flavor asymmetry x*(\Delta \bar{u} - \Delta\bar{d}) in the helicity distributions, at Q²=2.5 GeV² compared to a theoretical prediction from the chiral quark soliton model (dashed curve with theoretical uncertainty band). The experimental error bars and bands have the same meaning as in Fig.2 (03-114)
*Colour (eps) *BW (eps) *Data

Dec 1, 2003
Quark Fragmentation to pi^+/-, pi⁰, K^+/-, p and pbar in the Nuclear Environment
A. Airapetian et al, Phys. Lett. B 577 (2003) 37-46 *PDF *PostScript
Eprint numbers: hep-ex/0307023 and DESY-03-088
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: HADRON-ATTENUATION
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : kinematic plan for hadron production in semi-inclusive DIS
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Figure 2 : Charged hadron multiplicity ratio R_M^h as a function of nu for z > 0.2. Targets: Krypton and Nitrogen
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Figure 3 : Charged hadron multiplicity ratio R_M^h as a function of z for nu > 7. GeV. Targets: Krypton and Nitrogen
*Colour (eps) *BW (eps) *Data

Figure 4a : Multiplicity ratio for identified pions, kaons, protons and antiprotons as a function of nu for z > 0.2 Target: Krypton
*Colour (eps) *BW (eps) *Data

Figure 4b : Multiplicity ratio for identified pions, kaons, protons and antiprotons as a function of z for nu > 7 GeV. Target: Krypton
*Colour (eps) *BW (eps) *Data

Figure 5 : Multiplicity ratio for charged hadrons as a function of pt² for z > 0.2 and nu > 7 GeV. Target: Krypton and Nitrogen
*Colour (eps) *BW (eps) *Data

Aug 18, 2003
Double-spin Asymmetries in the Cross Section of Diffractive rho⁰ and phi Production at Intermediate Energies
A. Airapetian et al, Eur. Phys. J. C 29, 171 - 179 (2003) *PDF *PostScript
Eprint numbers: hep-ex/0302012 and DESY-02-230
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: VECTOR-MESONS: asymmetry
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Exclusive rho⁰ invariant mass distribution with fits
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Figure 2 : Delta E (missing energy) distribution for exclusive rho⁰ production with fits
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Figure 3 : Exclusive phi invariant mass spectrum and delta E (missing energy) distribution, both with fits
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Figure 4 : A₁ for exclusive rho⁰ production vs x overlaid with a theory prediction. Targets: proton and deuteron
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Figure 5 : A₁ for exclusive rho⁰ production vs -t overlaid with a theory prediction. Targets: proton and deuteron
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Figure 6 : A₁ for exclusive rho⁰ production vs Q² overlaid with a theory prediction. Targets: proton and deuteron. Results for quasi-real photoproduction data are included
*Colour (eps)

Figure 7 : A_|| for exclusive rho⁰ production vs p_t and and the energy of the rho⁰ in quasi-real photoproduction. Targets: proton and deuteron
*Colour (eps) *Data

Aug 11, 2003
Erratum to K. Ackerstaff et al, Phys. Lett. B 475 (2000) 386
A. Airapetian et al, Phys. Lett.B 567 (2003) 339 *PDF *PostScript
Eprint numbers: hep-ex/0210067 and DESY-02-092
SUBJECT: F2: f2ratio
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : The nuclear-elastic Bethe-Heitler cross section on ¹⁴N
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Figure 2 : Ratio of track reconstruction efficiencies in $^1$H, $^3$He, $^{14}$N and $^{84}$Kr with respect to $^2$H as function of $x$
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Figure 3 : Comparison between data (open and closed circles) and MC simulation (histogram) for the ratio of fractional changes in the yields of nitrogen and deuterium when treating the upper and lower HERMES detector halves independently
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Figure 4 : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nucleus A and D versus x
*BW (eps) *Data

Figure 5a : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nitrogen and deuterium for fixed values of x as a function of Q²
*BW (eps) *Data

Figure 5b : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nitrogen and deuterium for fixed values of x as a function of epsilon
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Figure 6 : The isoscalar-corrected ratio R_A / R_D for several nuclei (A) with respect to deuterium as a function of Q² for four different x bins
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Figure 7 : The isoscalar-corrected ratio R_A / R_D for several nuclei (A) with respect to deuterium as a function of Q²
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May 15, 2003
Q² Dependence of Nuclear Transparency for (In)coherent rho⁰ Production
A. Airapetian et al, Phys. Rev. Lett. 90 (2003) 052501 *PDF *PostScript
Eprint numbers: hep-ex/0209072 and DESY-02-152
SUBJECT: VECTOR-MESONS: xsec
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Nuclear transperency as a function of coherence length for coherent and incoherent rho⁰ production on ¹⁴N
*Colour (eps) *Data

Figure 2 : Scatter plot of Q² versus coherence length for exclusive rho⁰ production on ¹⁴N and H
*Colour (eps)

Figure 3 : Nuclear transparency as a function of Q² in coherence length bins for coherent rho⁰ production on ¹⁴N
*Colour (eps)

Figure 4 : Same as Fig. 3 (03-062) but now for incoherent production on ¹⁴N
*Colour (eps)

May 13, 2003
Measurement of Single-spin Azimuthal Asymmetries in Semi-inclusive Electroproduction of Pions and Kaons on a Longitudinally Polarized Deuterium Target
A. Airapetian et al, Phys. Lett. B562 (2003) 182 - 192 *PDF *PostScript
Eprint numbers: hep-ex/0212039 and DESY-02-226
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: AZIMUTHAL
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Diagram of the kinematics and angle definitions for azimuthal asymmetries
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Figure 2 : pi⁰ invariant mass spectrum with fit
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Figure 3 : Target spin asymmetry A_UL(phi) for pi⁺, pi^-, pi⁰ and K⁺ on a longitudinally polarised deuteron target. Two fits are shown with the data
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Figure 4 : Target spin analysing powers A_UL^sin(phi) for pi⁺, pi^-, pi⁰ and K⁺ on longitudinally polarised deuteron and proton targets vs different kinematic variables
*Colour (eps) *BW (eps) *Data

Figure 5 : Target spin analysing powers A_UL^sin(phi) for pi⁺, pi^-, pi⁰ and K⁺ on a longitudinally polarised deuteron vs x_Bj, compared to different model calculations
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Figure 6 : Target spin analysing powers A_UL^sin(2phi) for pi⁺, pi^-, pi⁰ and K⁺ on a longitudinally polarised deuteron vs x_Bj, compared to different model calculations
*Colour (eps) *BW (eps)

Figure 7 : Target spin analysing powers A_UL^sin(phi) for pi⁺, pi^-, pi⁰ on longitudinally polarised deuteron and proton targets vs z. The exclusive region is shown as well
*Colour (eps) *BW (eps)

Oct 31, 2002
Deep-inelastic Scattering on Nuclei
A. Airapetian et al, *PDF *PostScript
Eprint numbers: hep-ex/0210068 and DESY-02-091
INFO: This paper was never published only submittted in this version to hep-ex
SUBJECT: F2: f2ratio
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Ratio of track reconstruction efficiencies in $^1$H, $^3$He, $^{14}$N and $^{84}$Kr with respect to $^2$H as function of x
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Figure 2 : Comparison between data (points) and MC simulation (histogram) for the fractional change in the cross section ratios when treating the upper and lower HERMES detector halves independently
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Figure 3 : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nucleus A and D versus x. The error bars represent the statistical uncertainties, the systematic uncertainties are given by the error bandsi (ordered as HERMES, SLAC, NMC). The HERMES $^3$He/D and $^{14}$N/D data have been renormalised by 1.5%
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Figure 4a : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nucleus $A$ and $D$ as function of $Q²$ for fixed values of $x$. The error bars represent the statistical uncertainties. The HERMES $^{14}$N/D data have been renormalised by 1.5%
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Figure 4b : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nucleus $A$ and $D$ as function of $Q²$ for fixed values of $x$. The error bars represent the statistical uncertainties. The HERMES $^{14}$N/D data have been renormalised by 1.5%
*BW (eps)

Figure 5 : Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nitrogen and deuterium (renormalised by 1.5%) as function of $\epsilon$ for fixed values of $x$. The error bars represent the statistical uncertainties
*BW (eps)

Figure 6 : The isoscalar-corrected ratio $R_A / R_D$ for several nuclei (A) with respect to deuterium as a function of $Q²$ for four different x bins. The open triangles ($^{12}$C) and crosses ($^{4}$He) have been derived from the NMC data using Eq.~3. The other SLAC and NMC data displayed have been derived from published values of $\Delta R = R_A - R_D$ and a parameterisation for $R_D$. The inner error bars represent the statistical uncertainty and include the correlated error in $F₂^A/F₂^D$. The outer error bars represent the quadratic sum of the statistical and systematic uncertainties. In the upper panel the HERMES results at the lowest $Q²$ value have been suppressed because of its large error bar
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Figure 7 : The isoscalar-corrected ratio $R_A / R_D$ for several nuclei (A) with respect to deuterium as a function of $Q²$. The HERMES and NMC data have been combined in the determination of $R_A / R_D$. The other data are the same as in Fig. 6
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Oct 21, 2002
The Q² Dependence of the Generalized Gerasimov-Drell-Hearn Sum Rule for the Proton and the Neutron
A. Airapetian et al, EPJ C 26 (2003) 527-538 *PDF *PostScript
Eprint numbers: hep-ex/0210047 and DESY-02-172
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: G1: gdh
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Data-MC comparison of inclusive yield vs W² in the resonance region
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Figure 2 : Cross section difference Delta sigma for the deuteron target vs photon energy and for different Q² bins
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Figure 3 : Generalized GDH integral for the deuteron target vs Q² for all kinematic regions
*Colour (eps) *BW (eps)

Figure 4 : Cross section difference Delta sigma for the proton target vs photon energy and for different Q² bins
*BW (eps) *Data

Figure 5 : Generalized GDH integral for the proton target vs Q² for all kinematic regions
*Colour (eps) *BW (eps)

Figure 6 : Generalized GDH integral for the neutron (= deuteron - proton) vs Q² for all kinematic regions
*Colour (eps) *BW (eps)

Figure 7 : Generalized GDH integral for the neutron (= deuteron - proton) vs Q² for the DIS region
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Figure 8 : Generalized GDH integral for all targets (neutron, deuteron, proton) vs Q² for all kinematic regions
*Colour (eps) *BW (eps)

Figure 9 : Generalized GDH integral for neutron and proton targets vs Q², after dividing out the leading-twist Q² dependence
*Colour (eps) *BW (eps)

Figure 10 : Generalized GDH integral for the Proton - Neutron difference vs Q²
*Colour (eps) *BW (eps)

Apr 17, 2002
Single-spin Azimuthal Asymmetries in Electroproduction of Exclusive pi⁺
A. Airapetian, et al., Phys. Lett. B 535 (2002) 85-92 *PDF *PostScript
Eprint numbers: hep-ex/0112022 and DESY-01-223
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: AZIMUTHAL
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Missing mass distribution for $\pi^+$ (filled circles) and $\pi^-$ (empty circles) electroproduction at HERMES. The histogram is a Monte Carlo prediction for exclusive $\pi^+$ production with arbitrary normalization. b) Difference between the $\pi^+$ and normalized $\pi^-$ distributions (see text). The curve is a Gaussian fit to the data for $0.4X<1.2$ GeV. The vertical dotted line indicates the nucleon mass. The error bars represent the statistical uncertainties
*Colour (eps)

Figure 2 : $A_{\mathrm{UL}}^{\sin \phi}$ for the $e^+ + \vec{p} \rightarrow e^{\prime +} + h^+ + X$ reaction as a function of missing mass. The error bars represent the statistical uncertainties
*Colour (eps)

Figure 3 : Cross section asymmetry $A(\phi)$ averaged over $x$, $Q²$, and $t$ for the reaction $e^+ + \vec{p} \rightarrow e^{\prime +} + n + \pi^+$. The curve is the best fit to the data by $A(\phi) = A_{\mathrm{UL}}^{\sin \phi} \cdot \sin \phi$ with $ A_{\mathrm{UL}}^{\sin \phi} = -0.18 \pm 0.05$ at a reduced $\chi²$ of 0.8. The error bars and bands represent the statistical and systematic uncertainties, respectively
*Colour (eps)

Figure 4 : Kinematic dependence of $ A_UL^{\sin \phi}$ on the variables $x$, $Q²$, and $t$ for the reaction $e^+ + \vec{p} \rightarrow e^{\prime +} + n + \pi^+$. The error bars and bands represent the statistical and systematic uncertainties, respectively. The solid lines show the upper limits for any asymmetry arising from the transverse target polarization component. Table of data values in latex
*Colour (eps) *Data

Sep 11, 2001
Measurement of the Beam-Spin Azimuthal Asymmetry associated with Deeply-Virtual Compton Scattering
A. Airapetian et al., Phys. Rev. Lett. 87 (2001) 182001 *PDF *PostScript
Eprint numbers: hep-ex/0106068 and DESY-01-091
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: DVCS
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : (a) Feynman diagram for deeply-virtual Compton scattering, and (b) photon radiation from the incident and scattered lepton in the Bethe-Heitler process
*Colour (eps)

Figure 2: Plot 01-073 but including new contribution BH(N-Delta) which is plotted with pink color. The ratio of R=BH(N-Delta)/BH(N-N) was found to be on the level of 10% based on computation following paper by Frankfurt et al. hep-ph/9808449 for the average values of x,Q² and t and in the range of Mx<1.7 GeV
*Colour (eps)

Figure 2 : The measured distribution of photons observed in hard electroproduction versus the missing mass squared M_x². In the upper panel the full kinematic range is displayed, while the low M_x² domain is shown in the lower panel. The light-gray histogram represents the results of a Monte-Carlo simulation in which fragmentation processes and the Bethe-Heitler process are included, while the dark-shaded histogram represents only the BH contribution. The Monte-Carlo simulation includes the effect of the detector resolution
*Colour (eps)

Figure 3 : Beam-spin asymmetry A_LU for hard electroproduction of photons as a function of the azimuthal angle phi. The data correspond to the missing mass region between -1.5 and +1.7 GeV. The dashed curve represents a sin phi dependence with an amplitude of 0.23, while the solid curve represents the result of an SPD calculation taken from Ref.16. The horizontal error bars represent the bin width, and the error band below represents the systematic uncertainty
*Colour (eps) *Data

Figure 4 : The sin phi-moment A_LU^sin phi^+/- as a function of the missing mass for positive beam helicity (circles), negative beam helicity (squares) and the averaged helicity (open triangles). A negative value is assigned to M_x if M_x² lt 0. The error bars are statistical only. The systematic uncertainty is represented by the error band at the bottom of the figure
*Colour (eps) *Data

Figure 5 : The beam-spin analyzing power A_LU^sin phi for hard electroproduction of photons on hydrogen as a function of the missing mass. The systematic uncertainty is represented by the error band at the bottom of the figure
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Aug 1, 2001
Multiplicity of Charged and Neutral Pions in Deep-inelastic Scattering of 27.5 GeV Positrons
A. Airapetian et al, Eur.Phys.J. C21 (2001) 599-606 *PDF *PostScript
Eprint numbers: hep-ex/0104004 and DESY-01-037
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: FRAGMENTATION: pion
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Semi-inclusive pion electroproduction diagram
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Figure 2 : Two-photon invariant mass spectrum. The solid line is a fit with a Gaussian plus a polynomial. The dashed line represents the background only
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Figure 3 : Comparison between the measured and simulated pion energy spectra. Filled circles (triangles) are the neutral (charged) pion measurements. The histograms are the simulated spectra for neutral (dashed line) and charged (full line) pions. All spectra have been normalized to unit area
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Figure 4 : Detection probability as a function of z for charged (triangles) and neutral (circles) pions when the DIS positron is detected
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Figure 5a : Neutral (circles) and average charged (triangles) pion multiplicities. The error bars show the statistical uncertainty only. The systematic uncertainty for the charged (neutral) pions is 7percent (9percent). The solid line is a parameterization using the independent fragmentation model. The dashed line is a fit to the present neutral pion data using the parameterization given in the text. The charged pion data have been shifted slightly in z to make them visible
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Figure 5b : Ratio of neutral to average charged pion multiplicities. The systematic uncertainty on the ratio (not included in the error bar) is 6percent
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Figure 6a : pi⁰ multiplicity from HERMES, EMC and SLAC
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Figure 6b : Average charged pion multiplicity from HERMES compared to EMC fragmentation functions. Only the statistical uncertainties are s hown. The systematic uncertainties for neutral (charged) pions are 9percent (7percent) for HERMES, less than or equal 15percent for SLAC and less than or equal 13percent (10percent) for EMC
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Figure 7a : Multiplicities for neutral pions. The HERMES results have been evolved to Q²=25 GeV² using a NLO QCD model. Only statistical uncertainties are shown. The systematic uncertainties for neutral pions are 9percent for HERMES and less than or equal 13percent for EMC
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Figure 7b : Multiplicities for charged pions (note the EMC data for charged pions are for fragmentation functions). The HERMES results have been evolved to Q²=25 GeV² using a NLO QCD model. Only statistical uncertainties are shown. The systematic uncertainties for neutral pions are 7percent for HERMES and less than or equal 10percent for EMC
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Figure 8 : Charged pion multiplicities from HERMES (filled symbols) as a function of x in four different z-bins, compared to charged hadron multiplicities from EMC (open symbols). All data have been evolved to 2.5~GeV² and are plotted at the measured x-value
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Figure 9 : Total (neutral plus charged) pion multiplicity as a function of Q² for various z-bins. The systematic uncertainty on the data is 8.5percent. The three curves shown are NLO QCD calculations of fragmentation functions (see paper)
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Jul 29, 2001
Single Spin Azimuthal Asymmetry in Electroproduction of Neutral Pions in Semi-inclusive Deep Inelastic Scattering
A. Airapetian et al, Phys.Rev. D64 (2001) 097101 *PDF *PostScript
Eprint numbers: hep-ex/0104005 and DESY-01-047
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: AZIMUTHAL
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Analysing power in the sin phi moment for pi ^0 (circles) compared to previous results for pi^+ (triangles) and pi^- (squares) as a function of the pion fractional energy z, the Bjorken variable x and of the pion transverse momentum P_T. Error bars include the statistical uncertainties only. The filled and open bands at the bottom of the panels represent the systematic uncertainties for neutral and charged pions, respectively. The data for charged pion production are slightly shifted in z, x, and P_T for clarity. The shaded areas show a range of predictions of a model calculation applied to the case of pi⁰ electroproduction (see our paper)
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Jul 27, 2001
Hadron Formation in Deep-Inelastic Positron Scattering from ¹⁴N and ²H
A. Airapetian et al, Eur. Phys. J. C 20 (2001) 479-486 *PDF *PostScript
Eprint numbers: hep-ex/0012049 and DESY-00-191
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: HADRON-ATTENUATION
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Scatter plot of the hadron (or pion) energy E_h (E_pi) and the energy transfer nu. Lines representing constant values of z are shown as well
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Figure 2 : Charged hadron multiplicity ratio R_M^h as a function of nu for values of z larger than 0.2. In the upper panel the CERN and SLAC data for Cu are compared to various phenomenological calculations taken from the original publications. In the lower panel the HERMES data on nitrogen are represented by solid squares, while the open star represents the CERN data point on carbon and the open square the SLAC data point on carbon. The error bars represent the statistical uncertainty only. The systematic uncertainty of the HERMES data is less than 3 percent. The curves are described in the publication
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Figure 3 : The multiplicity ratio as a function of z for all charged pions (open circles) and all charged hadrons including pions (closed squares). The full curve represents a gluon-bremsstrahlung model calculation for pions. The dotted, dashed and dot-dashed curves represent phenomenological formation-time calculations
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Figure 4 : The multiplicity ratio as a function of nu for charged pions with z greater than 0.5. The solid curve represents a gluon-bremsstrahlung model calculation. The dotted curve is the result of a one time-scale model calculation assuming a (1-z)nu-dependence of the formation time
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Figure 5 : Multiplicity ratios for hadrons including pions (top panel) and identified pions (bottom panel) as a function of nu. The open (closed) squares represent the positive (negative) hadrons. Identified pions are represented by open (positive) and closed (negative) circles. The curves are parameterizations of the data using the one time-scale model assuming t_f^h = c_h (1-z)nu
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Jul 20, 2001
Measurement of Longitudinal Spin Transfer to Lambda Hyperons in Deep Inelastic Lepton Scattering
A. Airapetian et al, Phys.Rev. D64 (2001) 112005 *PDF *PostScript
Eprint numbers: hep-ex/9911017 and DESY-99-151
SUBJECT: LAMBDA-POL: longitudinal
CITATIONS: SPIRES at SLAC, DESY

Figure 1a : Lambda invariant mass spectrum, with highlighted signal and background regions
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Figure 1b : Spectrum of cos theta_pLambda for Lambda's reconstructed within the HERMES acceptance
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Figure 2 : Extracted spin transfer from virtual photon to Lambda, compared with theoretical curves
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Apr 6, 2001
Double-Spin Asymmetry in the Cross Section for Exclusive rho⁰ Production in Lepton-Nucleon Scattering
A. Airapetian et al, Phys. Lett. B 513 (2001) 301-310 *PDF *PostScript
Eprint numbers: hep-ex/0102037 and DESY-00-189
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: VECTOR-MESONS: asymmetry, rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Schematic graphs for various models of exclusive diffractive rho⁰ production: a) Reggeon or Pomeron exchange in models based on Regge theory, b) two-gluon exchange and c) quark exchange in models inspired by perturbative QCD
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Figure 2 : Distribution in the excitation energy Delta E for the decay channel rho⁰ to pi^+ pi^-, after all other event selection criteria were applied. The histogram is a Monte Carlo simulation of combinatorial background from deep-inelastic scattering (DIS). The shaded area indicates the events that were used for the analysis
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Figure 3a : Photon-nucleon asymmetry A₁^rho in exclusive rho⁰ production versus Q². Error bars and error bands denote the statistical and experimental systematic uncertainties, respectively
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Figure 3b : Photon-nucleon asymmetry A₁^rho in exclusive rho⁰ production versus W. Error bars and error bands denote the statistical and experimental systematic uncertainties, respectively
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Figure 3c : Photon-nucleon asymmetry A₁^rho in exclusive rho⁰ production versus x. Error bars and error bands denote the statistical and experimental systematic uncertainties, respectively
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Figure 3d : Photon-nucleon asymmetry A₁^rho in exclusive rho⁰ production versus -t'. Error bars and error bands denote the statistical and experimental systematic uncertainties, respectively
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Figure 3e : Photon-nucleon asymmetry A₁^rho in exclusive rho⁰ production versus Phi. Error bars and error bands denote the statistical and experimental systematic uncertainties, respectively
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Figure 3f : Photon-nucleon asymmetry A₁^rho in exclusive rho⁰ production versus theta. Error bars and error bands denote the statistical and experimental systematic uncertainties, respectively
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Figure 4 : Schematic graphs for exclusive rho⁰ production (a) and inclusive lepton-nucleon scattering (b)
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Nov 17, 2000
The Q²-dependence of the Generalised Gerasimov-Drell-Hearn Integral for the Proton
A. Airapetian et al, Phys. Lett. B 494 (2000) 1-8 *PDF *PostScript
Eprint numbers: hep-ex/0008037 and DESY-00-096
SUBJECT: G1: gdh, resonance
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Comparison of the event distribution for W² > 1GeV2 (squares) with the Monte-Carlo simulation (histogram). An overall normalisation factor was applied to the simulation to match the data. Also shown are the smeared distributions from the elastic, resonance and the deep inelastic regions. The vertical lines indicate the resonance region considered in the analysis
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Figure 2 : The GDH integral as a function of Q² for the region 1.0GeV2 < W² < 4.2GeV2. The error bars show the statistical uncertainties. The white and the hatched bands represent the systematic uncertainties with and without the A2 uncertainty contribution. The dashed and the solid curves are predictions based on a Q²-evolution of nucleon-resonance amplitudes
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Figure 3 : a) I(GDH) as a function of Q² for various upper limits of integration: W² < 4.2GeV2 (triangles), W² < 45GeV2 (squares), and the total integral I(GDH) (circles). The curve is the Soffer-Teryaev model for the total integral. b) I(GDH) Q² /(16 pi2 alpha) as a function of Q². For both panels, the error bars show the statistical uncertainties, and the white and the hatched bands at the bottom represent the systematic uncertainties for the total integral with and without the A2 contribution
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Nov 7, 2000
Exclusive Leptoproduction of rho⁰ Mesons on Hydrogen at Intermediate W Values
A. Airapetian et al, Eur. Phys. Jour. C 17 (2000) 389-398 *PDF *PostScript
Eprint numbers: hep-ex/0004023 and DESY-00-058
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: VECTOR-MESONS: xsec, rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Missing energy spectra for leptoproduction of rho⁰ mesons off H at an incident energy of 27.5 GeV
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Figure 2 : Invariant mass spectrum of the two oppositely charged hadrons assuming that they are pions
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Figure 3 : The virtual-photoproduction cross section for exclusive rho⁰ production versus W for the indicated values of average Q²
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Figure 4 : The virtual-photoproduction cross section for rho⁰ production on H versus Q²
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Figure 5 : The virtual-photoproduction cross section for rho⁰ production versus W at average Q² values of 0.83, 1.3, 2.3 and 4.0 GeV² (from top to bottom)
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Figure 6 : The longitudinal component of the virtual-photoproduction cross section for rho⁰ production versus W at average Q² values of 2.3 (left) and 4.0 GeV² (right)
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Nov 3, 2000
Measurement of Angular Distributions and R=sigma_L/sigma_T in Diffractive Electroproduction of rho⁰ Mesons
K. Ackerstaff et al, Eur. Phys. Jour. C 18 (2000) 303-316 *PDF *PostScript
Eprint numbers: hep-ex/0002016 and DESY-99-199
SUBJECT: VECTOR-MESONS: spin transfer, rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Diagram of diffractive rho production, showing rho decay to pi⁺ pi^-
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Figure 2 : Invariant mass spectrum for diffractive rho production from ³He
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Figure 3 : DeltaE spectrum for diffractive rho production from ³He
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Figure 4 : t' spectrum for diffractive rho production from ³He
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Figure 5 : Parametrization of DeltaE spectrum for double-diffractive dissociation (arbitrary units)
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Figure 6 : Diagram of the angles theta, phi, and Phi used to describe diffractive rho production and decay
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Figure 7 : Phase difference delta between the longitudinal and transverse amplitudes for diffractive rho production from ³He
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Figure 8 : Acceptance corrected cos(theta) spectrum for diffractive rho production from ³He
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Figure 9 : Acceptance corrected psi spectrum for diffractive rho production from ³He
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Figure 10 : Spin density matrix elements r⁰⁴₀₀ and r¹_1-1 for diffractive rho production from ³He
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Figure 11 : Acceptance corrected phi spectrum for diffractive rho production from ³He
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Figure 12 : Spin density matrix elements r⁰⁴_1-1 and r³_1-1 for diffractive rho production from ³He
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Figure 13 : Acceptance corrected Phi spectrum for diffractive rho production from ³He
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Figure 14 : Spin density matrix elements Tr(r¹), Tr(r⁵), and Tr(r⁸) for diffractive rho production from ³He
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Figure 15 : Ratio R = sigma_L/sigma_T for diffractive rho production from ³He
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May 3, 2000
Observation of a Single-Spin Azimuthal Asymmetry in Semi-Inclusive Pion Electro-Production
A. Airapetian et al, Phys. Rev. Lett. 84 (2000) 4047-4051 *PDF *PostScript
Eprint numbers: hep-ex/9910062 and DESY-99-149
SUBJECT: AZIMUTHAL: pi-proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : Diagram of kinematic planes and azimuthal angle phi for pion production in semi-inclusive DIS
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Figure 2 : Azimuthal sin(phi) and sin(2phi) moments of A_UL vs x, for pi⁺ production
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Figure 3 : Azimuthal sin(phi) moment of A_UL vs p_T, for pi⁺ (red squares) and pi^- (blue circles) production
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Mar 20, 2000
Nuclear Effects on R=sigma_L/sigma_T in Deep Inelastic Scattering
K. Ackerstaff et al, Phys. Lett. B 475 (2000) 386-394 *PDF *PostScript
Eprint numbers: hep-ex/9910071 and DESY-99-150
INFO: 2002: The data have been re-analysed. Erratum: A. Airapetian et al, Phys. Lett.B 567 (2003) 339 Please contact the Hermes management for further information.
Summary of paper for the general science reader: *PDF *PostScript
SUBJECT: F2: f2ratio
CITATIONS: SPIRES at SLAC, DESY

Figure 1 : DIS cross section ratio vs x for ¹⁴N/D (top panel) and ³He/D (bottom panel), overlaid with ¹²C/D and ⁴He/D data from NMC, SLAC, and E665
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Figure 2 : DIS cross section ratio vs Q², in x slices for ¹⁴N/D (solid circles), overlaid with ¹²C/D data from NMC (open squares)
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Figure 3 : DIS cross section ratio vs epsilon, in x slices for ¹⁴N/D (solid circles), overlaid with ¹²C/D data from NMC (open squares)
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Figure 4 : F₂ ratio vs x for ¹⁴N/D (top panel) and ³He/D (bottom panel), overlaid with parametrizations of ¹²C/D and ⁴He/D data from NMC and SLAC
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Figure 5 : R ratio for ¹⁴N/D and ³He/D, overlaid with data from NMC and SLAC for various nuclei
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Mar 20, 2000
Measurement of the Spin Asymmetry in the Photoproduction of Pairs of High-p_T Hadrons at HERMES
A. Airapetian et al, Phys. Rev. Lett. 84 (2000) 2584-2588 *PDF *PostScript
Eprint numbers: hep-ex/9907020 and DESY-99-071
SUBJECT: HIGH-PT
CITATIONS: SPIRES at SLAC, DESY

Figure 1: A_parallel for high-p_T hadron pairs in 2 views: top (bottom) panel has positive (negative) hadron p_T > 1.5
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Figure 2: Comparison of data and PYTHIA Monte Carlo for yield of hadron pairs vs p_T^h2, with p_T^h1 > 1.5
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Figure 3: Measured A_parallel for hadrons pairs vs p_T^h2, overlaid with Monte Carlo predictions for various values of deltaG/G
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Figure 4: Best fit deltaG/G point vs x_G, overlaid with four theoretical parametrizations
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Jan 13, 2000
Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-Inclusive Deep-inelastic Scattering
K. Ackerstaff et al, Phys. Lett. B464 (1999) 123-134 *PDF *PostScript
Eprint numbers: hep-ex/9906035 and DESY-99-048
SUBJECT: DELTA-Q
CITATIONS: SPIRES at SLAC, DESY

Figure 1: Six input asymmetries used for delta-q extraction
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Figure 2: Extracted quark polarizations, flavour symmetric decomposition
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Figure 3: The x-weighted quark spin distributions in the flavour symmetric decomposition
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Figure 4: The x-weighted quark spin distributions in the valence-sea decomposition, overlaid with data from SMC
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Figure 5: The x-weighted non-singlet quark spin distribution
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Figure 6: The x-weighted octet quark spin distribution, separately shown for our two sea polarization assumptions
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Nov, 1998
Observation of a Coherence Length Effect in Exclusive rho⁰ Electroproduction
K. Ackerstaff et al, Phys. Rev. Lett. 82 (1999) 3025-3029 *PDF *PostScript
Eprint numbers: hep-ex/9811011 and DESY-98-178
SUBJECT: VECTOR-MESONS: coherence length, rho
CITATIONS: SPIRES at SLAC, DESY

Figure 1: Spectrum of diffractive rho events vs deltaE and invariant mass
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Figure 2: Distribution of momentum transfer t' for exclusive rho production from ¹H, ²H, ³He, ¹⁴N
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Figure 3: Nuclear transparency T_A as a function of coherence length for ²H, ³He, ¹⁴N
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Sep, 1998
Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron
K. Ackerstaff et al, Phys. Lett. B444 (1998) 531-538 *PDF *PostScript
Eprint numbers: hep-ex/9809015 and DESY-98-122
SUBJECT: G1: gdh
CITATIONS: SPIRES at SLAC, DESY

Figure 1: Kinematic plane (Q²,nu) of the GDH analysis
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Figure 2: Cross section difference for proton and neutron from the GDH analysis
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Figure 2left: Cross section difference for the proton from the GDH analysis
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Figure 2right: Cross section difference for the neutron from the GDH analysis
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Figure 3a: DIS contribution to the GDH integral for the proton
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Figure 3b: DIS contribution to the GDH integral for the neutron
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Jul, 1998
Measurement of the Proton Spin Structure Function g₁^p with a Pure Hydrogen Target
A. Airapetian et al, Phys. Lett. B442 (1998) 484-492 *PDF *PostScript
Eprint numbers: hep-ex/9807015 and DESY-98-072
SUBJECT: G1: proton
CITATIONS: SPIRES at SLAC, DESY

Figure 1: Final result for g₁/F₁ from 97 data
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Figure 2: Final result for g₁/F₁ from 97 data in comparison to SLAC-E143 and SMC
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Figure 3: Final result for g₁^p from 97 data in comparison to SLAC-E143 (Q²=2 GeV**2) and SMC (Q²=10 GeV**2)
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Jul, 1998
The Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-inelastic Scattering
K. Ackerstaff et al, Phys. Rev. Lett. 81 (1998) 5519-5523 *PDF *PostScript
Eprint numbers: hep-ex/9807013 and DESY-98-078
SUBJECT: UNPOL-PDF: sea-flavour
CITATIONS: SPIRES at SLAC, DESY

Figure 1: Final result for dbar-ubar vs z
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Figure 2: Final result for dbar-ubar vs x (a) dbar-ubar/u-d (b) dbar/ubar in comparison to E866
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Jun, 1998
Beam-Induced Nuclear Depolarisation in a Gaseous Polarised Hydrogen Target
K. Ackerstaff et al., Phys. Rev. Lett. 82 (1999) 1164-1168 *PDF *PostScript
Eprint numbers: hep-ex/9806006 and DESY-98-058
SUBJECT: EXPERIMENT: target
CITATIONS: SPIRES at SLAC, DESY

Jun, 1998
The HERMES Spectrometer
K. Ackerstaff et al., Nucl. Instr. and Meth. A417 (1998) 230 *PDF *PostScript
Eprint numbers: hep-ex/9806008 and DESY-98-057
SUBJECT: EXPERIMENT: spectrometer
CITATIONS: SPIRES at SLAC, DESY

Mar 19, 1997
Measurement of the neutron spin structure function g₁ⁿ with a polarized ³He internal target
K. Ackerstaff et al, Phys. Lett. B 404 (1997) 383-389 *PDF
Eprint numbers: hep-ex/9703005 and DESY-97-085
INFO: DOI: 10.1016/S0370-2693(97)00611-4
SUBJECT: G1: neutron
CITATIONS: SPIRES at SLAC, DESY