# 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

14 December 2018

Abstract: Using data samples of $89.5\text{}\text{}{\mathrm{fb}}^{-1}$, $711.0\text{}\text{}{\mathrm{fb}}^{-1}$, and $121.4\text{}\text{}{\mathrm{fb}}^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{-}$ collider at center-of-mass energies 10.52, 10.58, 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 $\sqrt{s}=10.58\text{}\text{}\mathrm{GeV}$ 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 (${\sigma }_{B}$) 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 ${\sigma }_{B}\left({e}^{+}{e}^{-}\to \gamma {\chi }_{c1}\right)$ is obtained.

Published in: Physical Review D 98 (2018)