Diffractive photoproduction of J/#psi# mesons with large momentum transfer at HERA

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)/dt is studied in the range 2< vertical stroke t vertical stroke < 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_#gamma#_p in three t intervals, spanning the range 50< W_#gamma#_p <200 GeV. A fast rise of the cross section with W_#gamma#_p is observed for each t range and the slope for the effective linear Pomeron trajectory is measured to be #alpha#'=-0.0135#+-#0.0074(stat.)#+-#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. (orig.)Available from TIB Hannover: RA 2999(03-0610) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman