Experimental Results from HERA-I

In this section an overview of the results and measurements obtained with HERA-I data is given. In general, due to acceptance limitations of the experimental apparatus, the measurements are performed in restricted kinematic regions, which differ between different analyses, depending on the analysis technique and data sample. The tables 1, 2, 3 give an overview of the measurements of charm and beauty processes at HERA.

In order to allow for comparisons of measurements with results from other experiments or with theory predictions most analyses perform extrapolations of their data into unmeasured regions. The size of the corrections are often as small as a few percent but can reach a factor of order 10 in rare cases. In analyses using $D^*$-mesons the momentum and angular distributions of the decay particles ($K\pi\pi$) are usually assumed to be known and are extrapolated, such that the quoted cross sections are independent of the detector-specific cuts on the decay particles. These corrections are typically of order 25% reaching up to 50% at small values of $p_t(D^*)$. In analyses with jets, detector effects are removed by correcting the measured distributions to the hadron-level. Depending on the analysis the hadron-level may be differently defined, e.g. using the heavy hadrons before or after the decay and including or excluding neutrinos. In some analyses, the results are extrapolated to a larger phase space using model assumptions (as taken from next-to-leading order (NLO) calculations or LO+PS Monte Carlo models) of the angular and momentum spectra of the particles and jets. In these cases the extrapolation factors can become fairly large leading to corrections of the cross sections of up to a factor of 5. The uncertainties arising from these extrapolations are therefore often difficult to determine and the extrapolated results should be treated with caution.