Nuclear capture at rest of Ξ− hyperons

An emulsion-counter hybrid experiment (KEK E176) was carried out to search for double strangeness systems such as double-Λ hypernuclei and H-dibaryons. More than 10% of Ξ− hyperons produced in the (K−, K+) reaction were brought to rest in the nuclear emulsion. We have obtained 98 candidate events of nuclear capture at rest of Ξ− hyperons which are described in this report. Among those, four events were identified as sequential weak decay of double-Λ hypernuclei. The binding energies of Ξ−-(12C, 14N and 16O) states have been estimated for two events which emit twin single-Λ hypernuclei back to back from the capture point. The Σ−p decay vertex of an H-dibaryon was searched for near the capture point and no evidence was observed. Upper limits for the branching ratio of H emission are 5-10% for a lifetime less than 0.1 ns at the 90% confidence level. The trapping probabilities of single and double strangeness to a nuclear fragment following Ξ− capture at rest have been studied.