Observation of $\eta_{c}(2S) \to K^{+}K^{-}\eta$

TL;DR

This paper reports the first observation of the decay $ ext{eta}_c(2S) o K^+ K^- ext{eta}$ using a large sample of $ ext{psi}(3686)$ events, measuring its branching fraction and ratio to another decay mode, with significance over 6 sigma.

Contribution

First observation of $ ext{eta}_c(2S) o K^+ K^- ext{eta}$ decay and measurement of its branching fraction and ratio to $ ext{eta}_c(2S) o K^+ K^- ext{pi}^0$, providing new experimental data.

Findings

Decay $ ext{eta}_c(2S) o K^+ K^- ext{eta}$ observed with 6.2 sigma significance.

Branching fraction of $ ext{eta}_c(2S) o K^+ K^- ext{eta}$ measured as approximately 3.42 x 10^{-3}.

Ratio of branching fractions $ ext{eta}_c(2S) o K^+ K^- ext{eta}$ to $ ext{eta}_c(2S) o K^+ K^- ext{pi}^0$ is about 1.49.

Abstract

By analyzing $(27.12 \pm 0.14)\times10^{8}$ $\psi(3686)$ events accumulated with the BESIII detector, the decay $\eta_{c}(2S) \to K^{+} K^{-} \eta$ is observed for the first time with a significance of $6.2\sigma$ after considering systematic uncertainties. The product of the branching fractions of $\psi(3686) \to \gamma\eta_{c}(2S)$ and $\eta_{c}(2S) \to K^{+} K^{-} \eta$ is measured to be $\mathcal{B}(\psi(3686) \to\gamma\eta_{c}(2S))\times \mathcal{B}(\eta_{c}(2S)\to K^{+} K^{-}\eta)=(2.39 \pm 0.32 \pm 0.34) \times 10^{-6}$, where the first uncertainty is statistical, and the second one is systematic. The branching fraction of $\eta_{c}(2S)\to K^{+} K^{-}\eta$ is determined to be $\mathcal{B}(\eta_{c}(2S)\to K^{+} K^{-}\eta) = (3.42 \pm 0.46 \pm 0.48 \pm 2.44) \times 10^{-3}$, where the third uncertainty is due to the branching fraction of $\psi(3686) \to \gamma\eta_{c}(2S)$. Using a recent BESIII measurement of $\mathcal{B} (\eta_{c}(2S) \to K^{+} K^{-}\pi^{0})$, we also determine the ratio between the branching fractions of $\eta_{c}(2S) \to K^{+} K^{-}\eta$ and $\eta_{c}(2S) \to K^{+} K^{-}\pi^{0}$ to be $1.49 \pm 0.22 \pm 0.25$, which is consistent with the previous result of BaBar at a comparable precision level.