Photoproduction of $J/\psi$ in association with a $c\bar{c}$ pair

Understand

Based on the color-singlet model, we investigate the photoproduction of $J/\psi$ associated with a $c \bar{c}$ pair with all subprocesses including the direct, single-resolved, and double-resolved channels.

• The amplitude squared of these subprocesses are obtained analytically.
• By choosing corresponding parameters, we give theoretical predictions for the $J/\psi$ transverse momentum distributions both at the LEPII and at the future photon colliders for these subprocesses.
• The numerical results show that at the LEPII these processes can not give enough contributions to account for the experimental data, and it indicates that the color-octet mechanism may still be needed.