Measurement of the Lambda to p mu /sup -/ nu branching ratio

A sample of 1.2*10/sup 6/ Lambda -hyperons was analyzed in order to detect the rare decay mode: Lambda to p mu /sup -/ nu . The Lambda - hyperons were produced by stopping K/sup -/-mesons in the 81 cm Saclay hydrogen bubble chamber at the CERN PS. The authors obtained for the branching ratio the value (1.4+or-0.5)*10/sup -4/ based on 20 events, of which 6 have to be attributed to the background from the reaction Lambda to p pi /sup -/, pi /sup -/ to mu /sup -/ nu . The background was determined by a Monte Carlo calculation. (5 refs)