Evidence for $\eta_c$(2S)$\to\pipieta$ decay

TL;DR

This paper reports the first evidence for the decay (2S)  ta, measured through radiative transitions in (3686) decays, with quantified branching fractions and statistical significance.

Contribution

It provides the first experimental evidence and measurement of the (2S)  ta decay, expanding understanding of charmonium state decays.

Findings

First evidence of (2S)  ta decay at 3.5 significance.

Measured product of branching fractions: (2.97 .81 .26) 0^{-6}.

Determined (2S)  ta branching fraction: (42.4 .6 .8 0.3) 0^{-4}.

Abstract

The decay $\eta_c(2S)\to\pipieta$ is searched for through the radiative transition $\psi(3686) \to\gamma\eta_c(2S)$ using 448 million $\psi$(3686) events accumulated at the BESIII detector. The first evidence of $\eta_c(2S)\to\pi^+\pi^-\eta$ is found with a statistical significance of 3.5$\sigma$. The product of the branching fractions of $\psi(3686)\to\gamma\eta_c(2S)$ and $\eta_c(2S)\to\pipieta$ is measured to be $Br(\psi(3686)\to\gamma\eta_c(2S))\times Br(\eta_c(2S)\to\pipieta)=(2.97\pm0.81\pm0.26)\times10^{-6}$, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay $\eta_c(2S)\to\pipieta$ is determined to be $Br(\eta_c(2S)\to\pipieta)=(42.4\pm11.6\pm3.8\pm30.3)\times10^{-4}$, where the third uncertainty is transferred from the uncertainty of the branching fraction of $\psi(3686)\to\gamma\eta_c(2S)$.