We study radiative double-charmonium production, $e^+e^-\to HH\gamma$ with $H=J/\psi$ and $\eta_c$, at $\sqrt{s}=10.58~{\rm GeV}$, including a possible tensor contribution from the fully charmed state $X(6900)$. The nonresonant amplitudes are calculated within the color-singlet non-relativistic QCD framework, while the $J^{PC}=2^{++}$ resonance is combined coherently with the continuum. We find that continuum--resonance interference significantly modifies the invariant-mass distributions near $M_{HH}\simeq M_X$. The $J/\psi J/\psi\gamma$ channel exhibits a pronounced phase-dependent resonant structure, with a near-resonance cross section of $0.038$--$0.111~{\rm fb}$. In contrast, the $\eta_c\eta_c\gamma$ channel is continuum dominated and shows only a localized interference effect with an extremely suppressed production rate, rendering its experimental observation extremely challenging. These channel-dependent features arise from the different effective decay structures and demonstrate the importance of an amplitude-level treatment of the $X(6900)$ contribution.
Meng Jia, Yi-Jie Li, Guanghua Xu et al.· 1 citation
We revisit the calculations of relativistic corrections to inclusive $J/\psi$ production at B factories. For quark-level subprocesses with three-body final states, we carry out a full expansion of the final-state kinematic parameters. The resulting cross sections are theoretically self-consistent and independent of the choice of integration variables. In the high-energy limit, both cross-section magnitudes and the line shapes of correction curves for energy and momentum distributions agree remarkably well with fragmentation-function calculations. We find that $\mathcal{O}(v^2)$ corrections suppress the cross section by roughly $14.55\%$ in the $J/\psi + X_{c\bar{c}}$ channel and enhance it by approximately $12.18\%$ for the $J/\psi + X_{\text{non-}c\bar{c}}$ channel. After incorporating published $\mathcal{O}(\alpha_s)$ corrections, color-octet contributions, two-photon production channels, and feed-down effects, tension persists between theoretical predictions and experimental measurements. This indicates that complete prompt-quarkonium calculations through $\mathcal{O}(\alpha_s, v^2)$, or evaluations incorporating higher-order corrections, are required to resolve this tension.
Sheng-Juan Jiang, Sai Cui, Guanghua Xu et al.· 0 citations
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