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

TL;DR

This paper studies the production mechanisms of $J/ar{c}$ in electron-proton collisions, highlighting the roles of QED and QCD subprocesses, and their impact on cross sections and polarization, with implications for understanding color-octet matrix elements.

Contribution

It provides a detailed analysis of $J/ar{c}$ production at ep colliders, emphasizing the significance of QED and color-octet contributions, and their effects on cross sections and polarization.

Findings

QED subprocess enhances large $p_t$ differential cross section.

Color-octet subprocess increases cross section by a factor of 5 at large $p_t$.

$J/ar{c}$ polarization becomes more transverse with increasing $p_t$.

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.