Search for the decay $J/\ddot{I}ˆ\to {\hat{I}}^3+\mathrm{invisible}$

Abstract

We search for $J/\ddot{I}ˆ$ radiative decays into a weakly interacting neutral particle, namely an invisible particle, using the $J/\ddot{I}ˆ$ produced through the process $\ddot{I}ˆ(3686)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$ in a data sample of $(448.1\pm 2.9)\times 10^6$ $\ddot{I}ˆ(3686)$ decays collected by the BESIII detector at BEPCII. No significant signal is observed. Using a modified frequentist method, upper limits on the branching fractions are set under different assumptions of invisible particle masses up to 1.2 $\mathrm{Ge}\mathrm{V}/c^2$. The upper limit corresponding to an invisible particle with zero mass is 7.0$\times 10^{-7}$ at the 90\% confidence level.