Inclusive productions of $J/ψ+η_c$ in $e^{+}e^{-}$ annihilation at Belle

Abstract: We study $e^{{+}e^{-}} \to J/ψ+η_c+X$ at next-to-leading order (NLO) in $α_s$ within the nonrelativistic QCD (NRQCD) framework to assess the color-octet (CO) mechanism at low energies. QCD corrections significantly enhance both color-singlet (CS) and CO leading-order results, with non-negligible QED-diagram contributions to the CS channel. At $Υ(4S)$, CO terms increase the inclusive cross section by $20\%$--$30\%$, and the enhancement grows rapidly with $\sqrt{s}$, yielding an energy dependence distinct from CS predictions and providing a sensitive test of NRQCD. Including $ψ(2S)$ feed-down further amplifies the NRQCD prediction by about $40\%$ at $Υ(4S)$. With Belle's reconstruction of $J/ψ\to μ<sup>+μ<sup>-$ and six $η_c$ decay channels, the process shows promising potential for observation.