Suppression factors in diffractive photoproduction of dijets

After new publications of H1 data for the diffractive photoproduction of dijets, which overlap with the earlier published H1 data and the recently published data of the ZEUS collaboration, have appeared, we have recalculated the cross sections for this process in next-to-leading order (NLO) of perturbative QCD to see whether they can be interpreted consistently. The results of these calculations are compared to the data of both collaborations. We find that the NLO cross sections disagree with the data, showing that factorization breaking occurs at that order. If direct and resolved contributions are both suppressed by the same amount, the global suppression factor depends on the transverse-energy cut. However, by suppressing only the resolved contribution, also reasonably good agreement with all the data is found with a suppression factor independent of the transverse-energy cut.Comment: 28 pages, 11 figures, 3 table

Exclusive diffractive production of real photons and vector mesons in a factorized Regge-pole model with non-linear Pomeron trajectory

Exclusive diffractive production of real photons and vector mesons in ep collisions has been studied at HERA in a wide kinematic range. Here we present and discuss a Regge-type model of real photon production (Deeply Virtual Compton Scattering), as well as production of vector mesons (VMP) treated on the same footing by using an extension of a factorized Regge-pole model proposed earlier. The model has been fitted to the HERA data. Despite the very small number of the free parameters, the model gives a satisfactory description of the experimental data, both for the total cross section as a function of the photon virtuality Q2 or the energy W in the center of mass of the gamma\star-p system, and the differential cross sections as a function of the squared four-momentum transfer t with fixed Q2 and W.Comment: 34 pages, 82 figures accepted by Physical Review

Inclusive Diffraction at HERA

New precision measurements of inclusive diffractive deep-inelastic ep scattering interactions, performed by the H1 and ZEUS collaborations at the HERA collider, are discussed. A new set of diffractive parton distributions, determined from recent high precision H1 data, is presented.Comment: 5 pages, to appear in the proceedings of the 31st Intl. Conference on High Energy Physics ICHEP 2002, Amsterdam, July 200

Charm and Beauty Photoproduction at HERA

After the completion of data taking at HERA-2, a large data set is at hand to study the photoproduction of charm and beauty quarks in ep collisions. New measurements of charm production based on D^* meson tagging and beauty production based on muon and electron reconstruction test perturbative QCD calculations with improved accuracy. In general, QCD calculations at NLO describe the data well. The scale uncertainties are, however, large and dominate over the experimental uncertainties, calling for more precise calculations.Comment: Parallel talk at ICHEP08, Philadelphia, USA, July 2008. 4 pages, LaTeX, 3 eps figure

Deep inelastic diffractive scattering at HERA

Recent high precision measurements of deep inelastic diffractive scattering at HERA are presented in an increased region of phase space. Current models for diffractive photon dissociation are compared to the data.Comment: 6 pages, 6 figures, talk presented at QCD03, Montpellier, France, July 2-9, 200