Next-to-leading order analysis of $J/ψ+ γ$ production in photon-photon collisions at CEPC

TL;DR

This paper presents a next-to-leading order NRQCD analysis of J/psi plus photon production in gamma-gamma collisions at CEPC. It finds the direct channel dominates, with NLO corrections significantly reducing the color-singlet contribution while color-octet channels contribute modestly to the rate. The predicted J/psi polarization is highly LDME dependent, with Sets 1 and 2 giving transverse polarization and Set 3 yielding near zero or longitudinal polarization, driven primarily by the 3P_J octet LDME. With an expected yield of about 10^3 events per year at CEPC, this process offers a clean, precise test of LDME universality and the longstanding J/psi polarization puzzles.

Abstract

We systematically investigate the production of $J/ψ+ γ$ in $γγ$ collisions at next-to-leading order in $α_s$ within nonrelativistic QCD (NRQCD) factorization. Calculations for CEPC energy region show the resolved photon contribution is negligible, while the direct photon process dominates, yielding substantial annual $J/ψ$ yields. Significant modifications to $J/ψ$ 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 $J/ψ$ associated with a photon in $γγ$ collisions provides a high-precision platform to test LDMEs universality and resolve longstanding $J/ψ$ polarization puzzles.

Figures (7)

• Figure 1: Differential cross sections for direct ($\mathrm{Dir}$), single-resolved ($\mathrm{SR}$), and double-resolved ($\mathrm{DR}$) processes. For the resolved processes, the GRS99 photon PDF is employed Gluck:1999ub.
• Figure 2: Representative Feynman diagrams for $\gamma+\gamma \to c\bar{c}[^3S_1^{[1]}]+\gamma$ production. The second diagram in the first row denotes the counter-term with heavy dot.
• Figure 3: The illustrative diagrams for $\gamma+\gamma \to c\bar{c}[^1S_0^{[8]},^3P_J^{[8]}]+\gamma+g$.
• Figure 4: The $p_t$ distributions for $J/\psi + \gamma$ production in $\gamma\gamma$ collisions.
• Figure 5: Comparison of $J/\psi$ polarization predictions between the CS model and full NRQCD factorization.