Deep inelastic scattering with leading protons or large rapidity gaps at HERA 

                            ZEUS Collaboration 

The dissociation of virtual photons, gamma* p -> X p, in events with a 
large rapidity gap between X and the outgoing proton, as well as in events 
in which the leading proton was directly measured, has been studied with 
the ZEUS detector at HERA. The data cover photon virtualities Q2 > 2 GeV2 
and gamma* p centre-of-mass energies 40 < W < 240 GeV, with MX > 2 GeV, 
where MX is the mass of the hadronic final state, X . Leading protons were 
detected in the ZEUS leading proton spectrometer. The cross section is 
presented as a function of t, the squared four-momentum transfer at the 
proton vertex and Phi, the azimuthal angle between the positron scattering 
plane and the proton scattering plane. It is also shown as a function of 
Q2 and xIP, the fraction of the proton's momentum carried by the 
diffractive exchange, as well as beta, the Bjorken variable defined with 
respect to the diffractive exchange.