Elastic Photoproduction of J/psi and Upsilon Mesons at HERA

TL;DR

This paper reports measurements of elastic photoproduction cross sections for J/psi and Upsilon mesons at HERA, analyzing their energy dependence and comparing results with QCD and pomeron exchange models.

Contribution

It extends the energy range of J/psi photoproduction measurements and provides detailed analysis of cross section dependencies and Regge trajectory parameters.

Findings

Energy dependence parameter delta=0.83+-0.07 for J/psi

Differential cross section analysis and Regge trajectory determination

Comparison of data with perturbative QCD and pomeron exchange models

Abstract

Cross sections for elastic photoproduction of J/Psi and Upsilon mesons are presented. For J/Psi mesons the dependence on the photon-proton centre-of-mass energy W_gammap is analysed in an extended range with respect to previous measurements of 26<=W_gammap<= 285 GeV. The measured energy dependence is parameterized as sigma_gammap proportional W_gammap^delta with delta=0.83+-0.07. The differential cross section dsigma/dt for J/Psi mesons is derived, its dependence on W_gammap 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/GeV^2. Models based on perturbative QCD and on pomeron exchange are compared to the data.