Observation of $e^+e^- \to \gamma \chi_{c1}$ and search for $e^+e^- \to \gamma \chi_{c0}, \gamma \chi_{c2},$ and $\gamma\eta_c$ at $\sqrt{s}$ near 10.6 GeV at Belle

TL;DR

This study reports the first observation of the process $e^+e^- o \gamma \chi_{c1}$ at 10.58 GeV, providing new insights into charmonium production and setting upper limits for related processes at various energies.

Contribution

First observation of $e^+e^- o \gamma \\chi_{c1}$ at 10.58 GeV and measurement of its energy dependence, with upper limits set for other charmonium states at different energies.

Findings

Significant $\gamma \chi_{c1}$ signal observed at 10.58 GeV.

No significant signals for $\gamma \chi_{c0}$, $\gamma \chi_{c2}$, and $\gamma \eta_c$.

Upper limits established for cross sections at various energies.

Abstract

Using data samples of 89.5~fb$^{-1}$, 711.0~fb$^{-1}$, and 121.4~fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at center-of-mass energies 10.52 GeV, 10.58 GeV, and 10.867 GeV, respectively, we study the exclusive reactions $e^+e^-\to\gamma\chi_{cJ}$ ($J = 0,~1,~2$) and $e^+e^-\to\gamma\eta_c$. A significant $\gamma \chi_{c1}$ signal is observed for the first time at $\sqrt{s}=10.58$ GeV with a significance of $5.1\sigma$ including systematic uncertainties. No significant excesses for $\gamma \chi_{c0}$, $\gamma \chi_{c2}$, and $\gamma \eta_c$ final states are found, and we set 90\% credibility level upper limits on the Born cross sections ($\sigma_{\rm B}$) at 10.52 GeV, 10.58 GeV, and 10.867~GeV. Together with cross sections measured by BESIII at lower center-of-mass energies, the energy dependency of $\sigma_{\rm B}(e^+e^-\to\gamma\chi_{c1})$ is obtained.