Photoproduction of J/ψ mesons at high energies in the parton model and KT -factorization approach

We consider $J/\ensuremath{\psi}$ meson photoproduction on protons at high energies at the leading order in ${\ensuremath{\alpha}}_{s}$ using the conventional parton model and the ${k}_{T}$-factorization approach of QCD. It is shown that in both cases the color singlet mechanism gives the correct description for experimental data from DESY HERA for the total cross section and for the $J/\ensuremath{\psi}$ meson z spectrum at realistic values of a c-quark mass and meson wave function at the origin $\ensuremath{\Psi}(0).$ At the same time our predictions for the ${p}_{T}$ spectrum of the $J/\ensuremath{\psi}$ meson and for the ${p}_{T}$ dependence of the spin parameter $\ensuremath{\alpha}$ obtained in the ${k}_{T}$-factorization approach are very different from the results obtained in the conventional parton model. Such an experimental study of a polarized $J/\ensuremath{\psi}$ meson production at large ${p}_{T}$ should be a direct test of BFKL gluons.