We report on an attempt to describe hard exclusive photoproduction of $J/Psi$ mesons, i.e. the reaction $gamma p to J/Psi p$, by means of a modified version of the hard-scattering approach, in which the proton is treated as a quark-diquark rather than a three-quark system. In order to improve the applicability of the model at momentum transfers of only a few GeV we take into account constituent-mass effects in the calculation of the perturbative scattering amplitude. With a standard $J/Psi$-meson distribution amplitude and diquark-model parameters adopted from preceding investigations of other photon-induced reactions our predictions for differential cross sections overestimate the naive extrapolation of the low-momentum transfer ZEUS data. Our results, however, reveal the importance of taking into account the charm-quark mass.
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