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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 $γc\to J/ψc$ 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 $z=E_J/E_γ<0.2$ the contribution of the $γc\to J/ψc$ 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.