Search for $\eta_{c}(2S)\to K^+ K^- \eta^{\prime}$ decay

TL;DR

This paper reports evidence for the decay of $ ext{η}_c(2S)$ into $K^+ K^- ext{η}′$ with a measured branching fraction, updates on related charmonium decays, and sets an upper limit on the production rate, using a large sample of $ ext{ψ}(3686)$ events.

Contribution

It provides the first evidence for $ ext{η}_c(2S) o K^+ K^- ext{η}′$ decay and improves measurements of related charmonium decay branching fractions.

Findings

Evidence for $ ext{η}_c(2S) o K^+ K^- ext{η}′$ decay with 3.1σ significance.

Measured branching fraction of $(12.24 extpm4.60 ext{(stat.)} extpm2.37 ext{(syst.)} extpm4.68 ext{(extr.)}) imes 10^{-4}$.

Updated branching fractions for $ ext{χ}_{c1,2} o K^+ K^- ext{η}′$ with improved precision.

Abstract

Using $(2.712\pm0.014)\times10^{9}$ $\psi(3686)$ events collected with the BESIII detector operating at the BEPCII, we find an evidence of the $\eta_{c}(2S)\to K^+ K^- \eta^{\prime}$ decay with a statistical significance of 3.1$\sigma$. Its decay branching fraction is measured to be $(12.24\pm4.60(\mathrm{stat.})\pm2.37(\mathrm{syst.})\pm4.68(\mathrm{extr.}))\times 10^{-4}$, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is from the branching fraction of the $\psi(3686)\to\gamma\eta_{c}(2S)$ decay. The upper limit on the product branching fraction $B[\psi(3686)\to\gamma\eta_{c}(2S)] \times$ $B[\eta_{c}(2S)\to K^+ K^- \eta^{\prime}]$ is set to be $1.14 \times 10^{-6}$ at $90\%$ confidence level. In addition, the branching fractions of $\chi_{c1}\to K^+ K^- \eta^{\prime}$ and $\chi_{c2}\to K^+ K^- \eta^{\prime}$ are updated to be $(8.47\pm0.09(\mathrm{stat.})\pm0.47(\mathrm{syst.}))\times 10^{-4}$ and $(1.53\pm0.04(\mathrm{stat.})\pm0.08(\mathrm{syst.}))\times 10^{-4}$, respectively. The precision is improved by twofold.