Kinematical analysis of $\Xi ^-$ hyperons stop event in KEK-E373 experiment

The purpose of the E373 experiment is to study S=-2 nuclear systems with hundreds stopping events of $\Xi ^{-}$ hyperons. $\Xi ^{-}$hyperon is captured in the emulsion, interacts with a proton, and two $\Lambda $ hyperons are produced, in usual. In this experiment, we found NAGARA event that was identified as the production and decay of ${ }_{\Lambda \Lambda }^6 He$ among seven candidate events of double hypernucleus. We found several hundreds' events showing the emission of charged particles at the $\Xi ^{-}$ stopping points. Among them, there are two events having very characteristic decay topology. Only two charged particles were emitted from $\Xi ^{-}$ hyperon capture point, and one of those particles associated with an energetic charged particle. By the kinematical analysis, one event was identified as a non-mesonic decay of $\Lambda ^4 H$, and another one is probably a decay of $\Sigma ^-$ hyperon which is produced by week interaction between double strangeness.