Trapping probability of strangeness via Xi^- hyperon capture at rest in nuclear emulsion

In the E373 experiment at KEK-PS, we have located nearly 2 × 104 stopping events of hyperon candidates in nuclear emulsion. Among these, the identification of the hyperon was performed with the constant sagitta (CS) method, by measuring multiple Coulomb scattering for 695 clear stopping events, stop, with emission of nuclear fragments due to negatively charged hadrons.With use of a Geant4 simulation, the parameters for the CS method were optimized and we obtained the number of real stopping events to be 432.3±7.6+ 0.0-14.0 with 3.2% systematic error by contamination by thehyperon.We have classified the events forhyperon capture by light (C, N, O) and heavy (Ag, Br) elements in the emulsion. The trapping probabilities of two hyperons for light and heavy nuclei were found to be 5.0±1.7% and 4.2±1.4%, respectively, for stop via hyperon capture at rest in the emulsion. For at least one trapping, the probabilities were 69.4 ± 8.1% for light nuclei and 51.1 ± 5.7% for heavy nuclei. These results allow us to present the trapping probabilities of hyperons via hyperon capture at rest in emulsion for the first time, because the previous E176 experiment showed the lower limits due to fewer statistics.