$J/\psi$ production at HERA in the color singlet model with $k_{\mathrm{T}}$ -factorization

Abstract

In the framework of the $k_{\mathrm{T}}$ -factorization QCD approach and the color singlet model we consider $J/\psi$ inelastic photo- and leptoproduction processes at HERA. We investigate the dependences of the single differential and double differential cross section on various forms of the unintegrated gluon distribution. The z and ${\vec p}_{\mathrm {T}}$ dependences of the spin alignment parameter $\alpha$ are presented also. Our theoretical predictions agree well with the recent data taken by the H1 and ZEUS collaborations at HERA. It is shown that the experimental study of the polarization $J/\psi$ mesons at the low value $Q^2 < 1{\mathrm {GeV}}^2$ is an additional test of BFKL gluon dynamics.