Hard Diffraction and Central Diffraction in Hadron–hadron and Photon–hadron Collisions∗

Hadron production in single and central diffraction dissociation is studied in a model which includes soft hadron interaction as controlled by a supercritical pomeron parametrization and hard diffraction. Hard diffraction is described using leading-order QCD matrix elements together with the parton distributions for the proton, the less well known photon parton densities and a conjectured parton distribution function for the pomeron. Within this model, particle production in collisions with pomerons exhibit properties like multiple soft interactions and multiple minijets, quite similar to hadron production in non-diffractive hadronic collisions at high energies. However, important differences occur in transverse momentum jet and hadron distributions. It is shown that the model is able to describe data on single diffractive hadron production from the CERN-SPS collider and from the HERA lepton-proton collider as well as first data on central diffraction dissociation. We present also model predictions for single and central diffraction at TEVATRON.