Measurement of inelastic J/psi production in deep inelastic scattering at HERA

The inelastic production of J/psi mesons in ep collisions has been studied with the ZEUS detector at HERA using an integrated luminosity of 109 pb-1 . The J/psi mesons were identified using the decay channel J/psi->mu+mu- . The measurements were performed in the kinematic range 2 < Q^2 < 80 GeV^2 , 50 < W < 250 GeV , 0.2 < z < 0.9 and -1.6 < Y_lab < 1.3 , where Q^2 is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the J/psi meson in the proton rest frame and Y_lab is the rapidity of the J/psi in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the kT-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement.