Measurements of inelastic J/#psi# and #psi#' photoproduction at HERA

The cross sections for inelastic photoproduction of J/#psi# and #psi#' mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 38.0 pb"-"1. The events were required to have 0.1 < z < 0.9 and 50 < W < 180 GeV, where z is the fraction of the incident photon energy carried by the J/#psi# in the proton rest frame and W is the photon-proton centre-of-mass energy. The #psi#' to J/#psi# cross-section ratio was measured in the range 0.55 < z < 0.9. The J/#psi# data, for various ranges of transverse momentum, are compared to theoretical models incorporating colour-singlet and colour-octet matrix elements. Predictions of a next-to-leading-order colour-singlet model give a good description of the data, although there is a large normalisation uncertainty. The J/#psi# helicity distribution for z > 0.4 is compared to leading-order QCD predictions. (orig.)Available from TIB Hannover: RA 2999(02-163) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman