Intrinsic Charm in Proton and J/ψ Photoproduction at High Energies

Based on a perturbative theory of quantum chromodynamics and non-relativistic quark model, associated J/ψ plus open charm photoproduction on charm quarks in a proton via partonic subprocess γc→ J/ψc is discussed. It is shown that the value and energy dependence of the cross section for such process remarkably depends on the choice of charm distribution function in a proton. In the region of small z = EJ/Eγ < 0.2 the contribution of the γc → J/ψc subprocess in the inelastic J/ψ photoproduction spectra is larger than the contribution of the photon-gluon fusion subprocess. At the energy range of HERA collider intrinsic charm contribution in the total inclusive J/ψ photoproduction cross section may be equal to 4% of the dominant contribution of photon-gluon fusion mechanism.