Abstract.
The cross sections for inelastic photoproduction of \(J/\psi\) and \(\psi^{\prime}\) 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 \(\psi^{\prime}\) 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.
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Received: 22 October 2002 / Published online: 14 February 2003
supported by the US Department of Energy
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The ZEUS Collaboration ., al., S. Measurements of inelastic \(J/\psi\) and \(\psi^{\prime}\) photoproduction at HERA. Eur. Phys. J. C 27, 173–188 (2003). https://doi.org/10.1140/epjc/s2002-01130-2
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DOI: https://doi.org/10.1140/epjc/s2002-01130-2