Next-to-leading order analysis of $J/\psi + \gamma$ production in photon-photon collisions at CEPC

Abstract

We systematically investigate the production of $J/\psi + \gamma$ in $\gamma\gamma$ collisions within nonrelativistic QCD (NRQCD) factorization, with the direct-photon channel calculated specifically up to the next-to-leading order in $\alpha_s$. Calculations for CEPC energy region show the resolved photon contribution is negligible, while the direct photon process dominates, yielding substantial annual $J/\psi$ yields. Significant modifications to $J/\psi$ polarization parameters emerge from color-octet mechanisms, and different NRQCD long distance matrix elements (LDMEs) further yield distinct polarization patterns. Furthermore, the polarization predictions are highly sensitive to the $^3P_J^{[8]}$ LDME, while being insensitive to the $^1S_0^{[8]}$ and $^3S_1^{[8]}$ LDMEs. Leveraging the cleaner environment of $e^+e^-$ collisions versus hadronic processes, the production of $J/\psi$ associated with a photon in $\gamma\gamma$ collisions provides a high-precision platform to test LDMEs universality and resolve longstanding $J/\psi$ polarization puzzles.