Observation of $\ddot{I}ˆ(3686)\to p\bar{p}\ddot{I}•$

Abstract

Using a data sample of $4.48\times 10^8$ $\psip$ events collected with the BESIII detector, we present a first observation of $\ddot{I}ˆ(3686)\to p\bar{p}\ddot{I}•$, and we measure its branching fraction to be $[6.06\pm 0.38($stat.$)\pm 0.48($syst.$)]\times 10^{-6}$. In contrast to the earlier discovery of a threshold enhancement in the $p\bar{p}$-mass spectrum of the channel $J/\ddot{I}ˆ\to {\hat{I}}^{3}p\bar{p}$, denoted as $X(p\bar{p})$, we do not find a similar enhancement in $\ddot{I}ˆ(3686)\to p\bar{p}\ddot{I}•$. An upper limit of $1.82\times 10^{-7}$ at the $90\%$ confidence level on the branching fraction of $\ddot{I}ˆ(3686)\to X(p\bar{p})\ddot{I}•\to p\bar{p}\ddot{I}•$ is obtained.