Nuclear capture at rest of Ξ− hyperons

Abstract 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 − -( 12 C, 14 N and 16 O) 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.