title: J/psi production at HERA.
abstract: We consider the J/psi photoproduction data collected at the DESY ep collider HERA in the light of next-to-leading order predictions for the color-singlet yield and polarization. We find that, while the shapes of inclusive distributions in the transverse momentum and inelasticity are well reproduced, the experimental rates are larger than those given by the color-singlet contribution alone. Furthermore, the next-to-leading order calculation predicts the J/psi's to be mostly longitudinally polarized at high transverse momentum in contrast with the trend of the preliminary data from the ZEUS Collaboration.
authors.affiliation: Center for Particle Physics and Phenomenology (CP3), Université catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Artoisenet
authors.forename: J
authors.initials: J
authors.lastname: Campbell
authors.forename: F
authors.initials: F
authors.lastname: Maltoni
authors.forename: F
authors.initials: F
authors.lastname: Tramontano