The weak decay of lambda hypernuclei

Experimental technique and results from a study of the weak decay modes of /sub Λ/5He are presented. The weak decay modes of lambda hypernuclei include the mesonic decays (Λ/→ p + π- and Λ → n + π0) and the nonmesonic decay modes (Λ + p → n + p and Λ + n → n + n) the /sub Λ/5He hypernuclei were produced with the K- + 6Li → π- +/sub Λ 6Li π- + Λ/6Li reaction followed by the strong decay /sub Λ/6Li → /sub Λ/5He + p. The incoming K- momentum was 800 MeV/c and the K-π angle was 100. The experiment was performed on the Low Energy Separated Beam (LESBI) at the Brookhaven National Laboratory AGS. The protons from the nonmesonic decay branch and the negative pion from the mesonic decay branch were detected in a 14 element scintillator range spectrometer. The neutrons from the nonmesonic decay branch were detected in an 18 element time-of-flight neutron detector array. The partial rates for all four of the decay modes are measured in this experiment. The total decay rate is also measured. The result for the total decay rate is 1.03 +- 0.08 in units of the free lambda decay rate. The results are compared to several calculations of /sub Λ/5He nonmesonic weak decay rates. The results are also compared to /sub Λ/12C weak decay rates previously measured by the CMU-BNL-Houston-New Mexico-Vassar collaboration. 57 refs., 98 figs., 26 tabs