Next-to-leading-order study of $J/\psi$ angular distributions in $e^{+}e^{-} \to J/\psi+\eta_c,\chi_{cJ}$ at $\sqrt{s} \approx 10.6$ GeV

TL;DR

This study performs a next-to-leading-order QCD analysis of $J/ar{psi}$ angular distributions in electron-positron collisions, providing refined theoretical predictions that are compared with experimental data.

Contribution

The paper offers the first NLO calculations of angular distribution parameters for $J/\psi$ production in $e^+e^-$ annihilation within NRQCD, including differential cross sections.

Findings

NLO corrections moderately enhance $ heta$-distribution parameters for $J/\psi+\chi_{c0,1}$.

NLO corrections significantly reduce the $ heta$-distribution parameter for $J/\psi+\chi_{c2}$.

Predicted $ heta$-distribution for $J/\psi+\eta_c$ agrees with Belle measurements, but discrepancies remain for $J/\psi+\chi_{c0}$.

Abstract

In this paper, we present a detailed next-to-leading-order (NLO) study of $J/\psi$ angular distributions in $e^{+}e^{-} \to J/\psi+\eta_c,\chi_{cJ}$ ($J=0,1,2$) within the nonrelativistic QCD factorization (NRQCD). The numerical NLO expressions for total and differential cross sections, i.e., $\frac{d\sigma}{d\cos\theta}=A+B\cos^2\theta$, are both derived. With the inclusion of the newly-calculated QCD corrections to $A$ and $B$, the $\alpha_{\theta}(= B/A)$ parameters in $J/\psi+\chi_{c0}$ and $J/\psi+\chi_{c1}$ are moderately enhanced, while the magnitude of ${\alpha_\theta}_{J/\psi+\chi_{c2}}$ is significantly reduced; regarding the production of $J/\psi+\eta_c$, the $\alpha_\theta$ value remains unchanged. By comparing with experiment, we find the predicted ${\alpha_\theta}_{J/\psi+\eta_c}$ is in good agreement with the $\textrm{B}\scriptsize{\textrm{ELLE}}$ measurement; however, ${\alpha_\theta}_{J/\psi+\chi_{c0}}$ is still totally incompatible with the experimental result, and this discrepancy seems to hardly be cured by proper choices of the charm-quark mass, the renormalization scale, and the NRQCD matrix elements.