Measurements of Diffractive Vector-Meson Photoproduction at High Momentum Transfer from the ZEUS Experiment at HERA

Abstract

We discuss recent preliminary results on the diffractive photoproduction of ρ0, ϕ, and J/ψ mesons at high momentum transfer reported by the ZEUS collaboration at HERA. A special-purpose calorimeter served to tag the quasi-real photons (Q2<0.01 GeV 2) in the process γ+p→ VM +Y, where Y represents a dissociated state of the proton. The resulting range in photon-proton center-of-mass energy extends from 80 to 120 GeV. The differential cross sections [Formula: see text] were obtained in the region |t| > 1.2 GeV 2, where t denotes the squared momentum transfer to the proton. The measurements provide good sensitivity to the observed power-law dependence [Formula: see text]. Over the region in momentum transfer covered by the data, the power is found to be approximately n ≃ 3 for ρ0 and ϕ photoproduction, and approximately n ≃ 2 for J/ψ photoproduction.