J/{psi} polarization in photoproduction up to the next-to-leading order of QCD

We investigate the J/{psi} polarization in photoproduction at the Hadron Electron Ring Accelerator (HERA) up to the next-to-leading order of QCD. The results show that the transverse momentum p{sub t} and energy fraction z distributions of J/{psi} production do not agree with the observed ones very well. The theoretical uncertainties for the z distributions of the J/{psi} polarization parameters with respect to various choices of the renormalization and factorization scales are too large to give a definite predication. The uncertainties for the p{sub t} distributions of these parameters are small when p{sub t}>3 GeV and the obtained p{sub t} distributions cannot describe the experimental data even in this region.