Search for $\eta_c(2S)\to p\bar{p}$ and branching fraction measurements of $\chi_{cJ} \to p\bar{p}$ via $\psi(2S)$ radiative decays

TL;DR

This study searches for the decay of $oldsymbol{ ext{eta}_c(2S)}$ to proton-antiproton pairs via $oldsymbol{ ext{psi}(2S)}$ radiative decays, setting upper limits and measuring branching fractions of related charmonium states using BESIII data.

Contribution

First measurement of $oldsymbol{ ext{eta}_c(2S)}$ to $oldsymbol{par{p}}$ decay with an upper limit, and precise measurements of $oldsymbol{ ext{chi}_{cJ}}$ to $oldsymbol{par{p}}$ branching fractions.

Findings

No significant $oldsymbol{ ext{eta}_c(2S)}$ to $oldsymbol{par{p}}$ signal detected.

Upper limit on $oldsymbol{ ext{BR}( ext{psi}(2S) o ext{gamma} ext{eta}_c(2S)) imes ext{BR}( ext{eta}_c(2S) o par{p})$ is $2.4 imes 10^{-7}$.

Measured branching fractions for $oldsymbol{ ext{chi}_{cJ} o par{p}}$ are consistent with previous results.

Abstract

Using $(27.12\pm0.14) \times 10^{8}$ $\psi(2S)$ events collected by the BESIII detector operating at BEPCII, we search for the decay $\eta_c(2S)\to p\bar{p}$ via the process $\psi(2S)\to \gamma\eta_c(2S)$, and only find a signal with a significance of $1.7\,\sigma$. The upper limit of the product branching fraction at the 90% confidence level is determined to be $\mathcal{B}(\psi(2S)\to \gamma\eta_c(2S))\times \mathcal{B}(\eta_c(2S)\to p\bar{p})<2.4\times 10^{-7}$. The branching fractions of $\chi_{cJ}\to p\bar{p}~(J=0,1,2)$ are also measured to be $\mathcal{B}(\chi_{c0}\to p\bar{p})=(2.51\pm0.02\pm0.08)\times 10^{-4}$, $\mathcal{B}(\chi_{c1}\to p\bar{p})=(8.16\pm0.09\pm0.25)\times 10^{-4}$, and $\mathcal{B}(\chi_{c2}\to p\bar{p})=(8.33\pm0.09\pm0.22)\times 10^{-4}$, where the first uncertainty is statistical and the second systematic.