Search for the baryon number and lepton number violating decays $\ddot{I}{„}^{-}\to \hat{I}›\ddot{I}{€}^{-}$ and $\ddot{I}{„}^{-}\to \bar{\hat{I}}›\ddot{I}{€}^{-}$ at Belle II

Abstract

We present a search for the baryon number $B$ and lepton number $L$ violating decays $\ddot{I}{„}^{-}\to \hat{I}›\ddot{I}{€}^{-}$ and $\ddot{I}{„}^{-}\to \bar{\hat{I}}›\ddot{I}{€}^{-}$ produced from the $e^{+}{e}^{-}\to \ddot{I}{„}^{+}\ddot{I}{„}^{-}$ process, using a 364 fb${}^{-1}$ data sample collected by the Belle~II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have $|\hat{I}”(B-L)|$ equal to $2$ and $0$, respectively. Upper limits at 90\% credibility level on the branching fractions of $\ddot{I}{„}^{-}\to \hat{I}›\ddot{I}{€}^{-}$ and $\ddot{I}{„}^{-}\to \bar{\hat{I}}›\ddot{I}{€}^{-}$ are determined to be $4.7\times 10^{-8}$ and $4.3\times 10^{-8}$, respectively.

8 pages, 4 figures