Weak decays of 4Λ He

We measured the lifetime and the mesonic and nonmesonic decay rates of the 4ΛHe hypemucleus. The hypemuclei were created using a 750 MeV/c momentum K - beam on a liquid 4 He target by the reaction 4 He(K - π - )4Λ He. The 4ΛHe lifetime was directly measured using protons from Ap → np nonmesonic decay (also referred to as proton-stimulated decay) and was found to have a value of T = 245 ± 24 ps. The mesonic decay rates were determined from the observed numbers of π - 's and π°'s as Γπ/ Γ tot = 0.270 ± 0.024 and Γπ°/ Γ tot = 0.564 ± 0.036, respectively, and the values of the proton- and neutron-stimulated decay rates were extracted as Fp/ r tot = 0.169 ± 0.019 and Γ n / Γ tot ≤0.032 (95% CL), respectively. The effects of final-state interactions and possible three-body ANN decay contributions were studied in the context of a simple model of nucleon-stimulated decay. Nucleon-nucleon coincidence events were observed and were used in the determination of the nonmesonic branching fractions. The implications of the results of this analysis were considered for the empirical ΔI = 1 2 rule and the decay rates of the 4ΛH hypemucleus.