Mesonic and non-mesonic decay widths of 4ΛH and 4ΛHe

Results are reported on precise measurements of the weak-decay processes of H-4(Lambda) and He-4(Lambda) hypernuclei formed via the He-4(K-stopped(-), pi(-)) reaction. The lifetimes of H-4(Lambda) (194(-26)(+24) ps) and He-4(Lambda) (256 +/- 27 ps) were obtained. The pi(0) and pi(-) decay branching ratios of He-4(Lambda) (0.515 +/- 0.035 and 0.322 +/- 0.034, respectively) were precisely determined and they are compared with recent theoretical estimates and related experimental values. Our results favor a Lambda-nucleus interaction with an inner repulsive core. The non-mesonic weak decay widths Of H-4(Lambda) and He-4(Lambda) are reexamined on the basis of our measurements and updated of the mesonic decay processes. It is found that the non-mesonic decay of He-4(Lambda) predominantly takes place via the Lambda + p --> n + p process.