CHARM CONTENT OF A PHOTON AND $J/\psi$ PHOTOPRODUCTION AT HIGH ENERGIES

Abstract

A study of the $J/\psi$-meson production at large transverse momentum in high energy $\gamma p$ collisions via the charm quark excitation in a photon is presented. Based on perturbative QCD and the nonrelativistic quark model, our calculation demonstrates that the charm content of a photon may be very important for the $J/\psi$ photoproduction at the large transverse momentum. It is shown that at HERA energies $J/\psi$ production via the subprocess $cg\to J/\si c$ dominates over the resolved photon contribution via the subprocess $gg\to J/\psi g$ at $p_{\bot}>3$ GeV/c and over the direct photon-gluon fusion contribution at $p_{bot}>10$ GeV/c.