Observation of ${\eta }_c\to p\bar{p}\eta$ via $\psi (3686)\to \gamma p\bar{p}\eta$

Abstract

The decay ${\eta }_c\to p\bar{p}\eta$ is observed for the first time with a significance of exceeding $10\sigma$. It is found by analyzing $(2712.4\pm 14.3)\times 10^6$ $\psi (3686)$ events accumulated at the BESIII detector. The measured branching fraction of ${\eta }_c\to p\bar{p}\eta$ via $\psi (3686)\to \gamma p\bar{p}\eta$ is significantly influenced by the interference between the resonant ${\eta }_c$ decay and the non-resonant process $\psi (3686)\to \gamma p\bar{p}\eta$ and is measured in both constructive- and destructive-interference scenarios. The joint branching fraction of $\psi (3686)\to \gamma {\eta }_c$, ${\eta }_c\to p\bar{p}\eta$ is measured to be $(3.2\pm 0.1\pm 0.9)\times 10^{-6}$ or $(8.7\pm 0.3\pm 2.1)\times 10^{-6}$ for constructive- or destructive-interference solutions, respectively, where the first uncertainties are statistical and the second systematic. The branching fraction of ${\eta }_c\to p\bar{p}\eta$ is determined to be $\mathcal{B}({\eta }_c\to p\bar{p}\eta )=(0.90\pm 0.04\pm 0.21\pm 0.13)\times 10^{-3}$ or $(2.42\pm 0.07\pm 0.48\pm 0.34)\times 10^{-3}$ for the two solutions, respectively, where the third uncertainties are due to the uncertainty in the branching fraction of $\psi (3686)\to \gamma {\eta }_c$.