Mesonic and non-mesonic decay widths of Λ4H and Λ4He

Results are reported on precise measurements of the weak-decay processes of Λ4H and Λ4He hypernuclei formed via the 4He(Kstopped-,π-) reaction. The lifetimes of Λ4H (194-26+24 ps) and Λ4He (256±27 ps) were obtained. The π0 and π- decay branching ratios of Λ4He (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 Λ-nucleus interaction with an inner repulsive core. The non-mesonic weak decay widths of Λ4H and Λ4He are reexamined on the basis of our measurements and updated knowledge of the mesonic decay processes. It is found that the non-mesonic decay of Λ4He predominantly takes place via the Λ+p→n+p process. (orig.)