Search for the lepton number violating decay $\hat{I}{\pounds }^{-}\to p{e}^{-}{e}^{-}$ and the rare inclusive decay $\hat{I}{\pounds }^{-}\to \hat{I}{\pounds }^{+}X$

Abstract

Using a data sample of $(1310.6\pm 7.0)\times 10^6$ $J/\ddot{I}ˆ$ events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay $\hat{I}{\pounds }^{-}\to p{e}^{-}{e}^{-}$ and the rare inclusive decay $\hat{I}{\pounds }^{-}\to \hat{I}{\pounds }^{+}X$, where $X$ denotes any possible particle combination. The $\hat{I}{\pounds }^{-}$ candidates are tagged in $J/\ddot{I}ˆ\to \bar{\hat{I}}\pounds (1385{)}^{+}\hat{I}{\pounds }^{-}$ decays. No signal candidates are found, and the upper limits on the branching fractions at the 90\% confidence level are determined to be $\mathcal{B}(\hat{I}{\pounds }^{-}\to p{e}^{-}{e}^{-})<6.7\times 10^{-5}$ and $\mathcal{B}(\hat{I}{\pounds }^{-}\to \hat{I}{\pounds }^{+}X)<1.2\times 10^{-4}$.