Measurement of inelastic J/ψ photoproduction at HERA

We present a measurement of the inelastic, non diffractive J/psi photoproduction cross section in the reaction e(+)p --> e(+)J/psi X with the ZEUS detector at HERA, The J/psi was identified using both the mu(+)mu(-) and e(+)e(-) decay channels and events were selected within the range 0.4 < z < 0.9 (0.5 < z < 0.9) for the muon (electron) decay mode, where z is the fraction of the photon energy carried by the J/psi in the proton rest frame. The cross section, the p(T)(2) and the z distributions, after having subtracted the contributions from resolved photon and diffractive proton dissociative processes, are given for the photon-proton centre of mass energy range 50 < W < 180 GeV; p(T)(2) is the square of the J/psi transverse momentum with respect to the incoming proton beam direction. In the kinematic range 0.4 < z < 0.9 and p(T)2 > 1 GeV(2), NLO calculations of the photon-gluon fusion process based on the colour-singlet model are in good agreement with the data, The predictions of a specific leading order colour-octet. model, as formulated to describe the CDP data on J/psi hadroproduction, are not consistent with the data.