Elastic and Proton-Dissociative Photoproduction of J/psi Mesons at HERA

Understand

Cross sections for elastic and proton-dissociative photoproduction of J/psi mesons are measured with the H1 detector in positron-proton collisions at HERA.

• The data were collected at $ep$ centre-of-mass energies sqrt{s} approx 318 GeV and sqrt{s} approx 225 GeV, corresponding to integrated luminosities of L = 130 pb^{-1} and L = 10.8 pb^{-1}, respectively.
• The cross sections are measured as a function of the photon-proton centre-of-mass energy in the range 25< Wgp < 110 GeV.
• Differential cross sections $\mathrm{d}\sigma / \mathrm{d}t$, where $t$ is the squared four-momentum transfer at the proton vertex, are measured in the range $|t| < 1.2 \, \gevsq$ for the elastic process and $|t| < 8 \, \gevsq$ for proton dissociation.