Coincidence measurement of the weak decay of 12ΛC and the three-body weak decay process (J-PARC 50GeV PS E18)

Recently we have reported the Γn/Γp value, ∼0.5, obtained in the exclusive coincidence measurement of the nucleon pairs in the back-to-back kinematics, which led to the resolution of the long standing Γn/Γp puzzle. We also have reported the branching ratio of the three-body process in the nonmesonic weak decay of 12ΛC to be 0.29 ± 0.13 by reproducing the quenching of the nucleon yields. At the same time we have finally obtained the absolute decay widths Γn and Γp taking account of the three-body processes. However, there still are serious inconsistencies not only between the experimental and theoretical values of important observables such as the decay asymmetry parameter αNM, but also between the basic formalisms of theoretical models. In order to provide more stringent guides for theoretical models, it is urgent to measure the fundamental observables, such as Γn, Γp, and Γ2N, with much improved accuracy. In this regards, the next extensive coincidence experiment is planned at the J-PARC 50GeV PS for the accurate determination of the decay widths to the level of ∼10% statistical uncertainty and the measurement of Γ2N in the exclusive way.