Diffractive Photoproduction of J/psi Mesons with Large Momentum Transfer at HERA

TL;DR

This paper reports on the measurement of diffractive photoproduction of J/psi mesons at HERA, analyzing how the cross section varies with momentum transfer and energy, and comparing results with QCD models.

Contribution

It provides new measurements of the differential cross section for J/psi photoproduction at large momentum transfer and compares these with perturbative QCD predictions, including BFKL and DGLAP models.

Findings

Cross section rises rapidly with energy W in all t ranges.

The slope of the Pomeron trajectory is measured as alpha' = -0.0135 ± 0.0074 (stat.) ± 0.0051 (syst.).

Data are consistent with s-channel helicity conservation.

Abstract

The diffractive photoproduction of J/psi mesons is measured with the H1 detector at the ep collider HERA using an integrated luminosity of 78 pb^-1. The differential cross section d sigma(gamma p -> J/psi Y) / d t is studied in the range 2 < |t| < 30 GeV^2, where t is the square of the four-momentum transferred at the proton vertex. The cross section is also presented as a function of the photon-proton centre-of-mass energy W in three t intervals, spanning the range 50 < W < 200 GeV. A fast rise of the cross section with W is observed for each t range and the slope for the effective linear Pomeron trajectory is measured to be alpha^\prime= -0.0135 \pm 0.0074 (stat.) \pm 0.0051 (syst.) GeV^-2. The measurements are compared with perturbative QCD models based on BFKL and DGLAP evolution. The data are found to be compatible with s-channel helicity conservation.