Elastic photoproduction of J/ψ and γ mesons at HERA

Cross sections for elastic photoproduction of J/psi and Y mesons are presented. For J/psi mesons the dependence on the photon-proton centre-of-mass energy W-gamma p is analysed in an extended range with respect to previous measurements of 26 less than or equal to W-gamma p less than or equal to 2.85 GeV. The measured energy dependence is parameterized as sigma(gamma p) proportional to W-gamma p(delta) with delta = 0.83 +/- 0.07. The vp UP YP differential cross section d sigma/dt for J/psi mesons is derived, its dependence on W-gamma p and on t is analysed and the effective trajectory (in terms of Regge theory) is determined to be alpha(t) = (1.27 +/- 0.05) + (0.08 +/- 0.17) . t/GeV2. Models based on perturbative QCD and on pomeron exchange are compared to the data. (C) 2000 Elsevier Science B.V. All rights reserved.