Mesonic and non-mesonic decay widths of ⁴_ΛH and ⁴_ΛHe

Results are reported on precise measurements of the weak-decay processes of ⁴_ΛH and ⁴_ΛHe hypernuclei formed via the ⁴He(K^-_stopped, π^-) reaction. The lifetimes of ⁴_ΛH (194⁺²⁴_-26 ps) and ⁴_ΛHe (256 ± 27 ps) were obtained. The π⁰ and π^- decay branching ratios of ⁴_ΛHe (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 Λnucleus interaction with an inner repulsive core. The non-mesonic weak decay widths of ⁴_ΛH and ⁴_ΛHe 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 ⁴_ΛHe predominantly takes place via the Λ + p → n + p process.