Measurement of inelastic J/ψ and ψ ′ photoproduction at HERA

The cross sections for inelastic photoproduction of J/ and ′ mesons have been measured in ep collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb−1 collected in the period 1996–2007. The ′ to J/ cross section ratio was measured in the range 0.55 <z <0.9 and 60 <W <190GeV as a function of W, z and pT . Here W denotes the photon-proton centre-of-mass energy, z is the fraction of the incident photon energy carried by the meson and pT is the transverse momentum of the meson with respect to the beam axis. The J/ cross sections were measured for 0.1 <z <0.9, 60 <W <240GeV and pT > 1GeV. Theoretical predictions within the nonrelativistic QCD framework including NLO colour-singlet and colour-octet contributions were compared to the data, as were predictions based on the kT -factorisation approach.