The Delta I=1/2 rule in non-mesonic weak decay of Lambda-hypernuclei

By employing recent data on non-mesonic decay of s-shell Lambda-hypernuclei we study, within the phenomenological model of Block and Dalitz, the valid ity of the Delta I = 1/2 rule in the Lambda N --> NN process. Due to the lo w experimental precision, a possible violation of this rule can be neither proved nor excluded at present with sufficient accuracy: a pure Delta I= 1/ 2 transition amplitude is excluded at 40% confidence level. (C) 2000 Elsevi er Science B.V. All rights reserved.