Exclusive Photoproduction at HERA

The exclusive Υ photoproduction, γ p → Υp, has been studied with the ZEUS experiment in ep collisions at HERA using an integrated luminosity of 468 pb−1. The measurement covers the kinematic range 60 < W < 220 GeV and Q2 < 1 GeV2, where W is the photon-proton centre-ofmass energy and Q2 is the photon virtuality. These results, which represent the analysis of the full ZEUS data sample for this channel, are compared to predictions based on perturbative QCD. The proton-dissociative diffractive photoproduction of J/ψ mesons, γ p → J/ψ Y , with Y being the proton dissociative system, has been studied in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 112 pb−1 in the range 30 <W < 160 GeV and 2 < |t|< 30 GeV2, where t is the four-momentum transfer squared at the proton vertex. The cross section is presented as a function of W and t. The results are compared to perturbative QCD calculations. The first measurement of diffractive scattering of quasi-real photons with large momentum transfer γ p → γY was made using the H1 detector at HERA. The measurement is performed for initial photon virtualities Q2 < 0.01 GeV2. Cross sections are measured as a function of W and t in the range 175 < W < 247 GeV and 4 < |t| < 36 GeV2. The data are compared to a model based on perturbative QCD using a leading-logarithmic approximation of the BFKL evolution. Based on data collected with the H1 detector at HERA in 2005, cross sections for elastic ρ photoproduction have been measured at |t| < 0.58 GeV2 and 8 < W < 94 GeV. This data has been combined with cross sections published previously by the Omega and ZEUS collaborations in a global fit to determine the Pomeron trajectory α(t) in 13 bins of t from the W -dependence of the elastic ρ production cross section.