The production of $J/\psi$ associated with $c\bar{c}$ at ep colliders

Abstract

We investigate the direct photoproduction of $J/\psi+c\bar{c}$ at $ep$ colliders with different center of mass energies in this paper. For the color-singlet part we take into account the contribution from QED subprocess as well as the QCD one. Our results show that the QED subprocess not only enhances the differential cross section in the large $p_t$ region but also gives a more transverse $J/\psi$ with $p_t$ increase, which is different from the almost unpolarized $J/\psi$ predicted by the QCD subprocess. The contribution from color octet subprocesses enhances the differential cross section by a factor of 5 in large $p_t$ region and predicts an even more transverse $J/\psi$ in the medium and large $p_t$ region. The sensitivity of this process to the color-octet matrix element $\langle O^{J/\psi}(^3S_1^8)\rangle$ may give great help in studying the matrix element.