Recent Progress on Three-Body Nonmesonic Weak Decay of A Hypernuclei

摘要

One important recent developement of nonmesonic weak decay (NMWD) study of hypernuclei is the experimentatl confirmation of three-body NMWD and the finding of its big branching ratio, which is comparable to those of two-body NMWD channels. The implication is that the current values of Γ_n and Γ_p, which are fundamentally important for the study of baryon-baryon weak interaction but have been determined without taking accounts of the three-body NMWD, should be significanly modified. We have recently obtained the branching ratio of the three-body NMWD attributing the quenching of nucleon yields in the NMWD due to the presence of the three-body NMWD. In order to disentangle the effects of the final state interaction (FSI), which occupies the same three-body phase space as the three-body NMWD, we adopted a novel renormalization method of INC (Intranuclear Cascade) calculation. We obtained the branching ratios, Γ_(2N)/Γ_(nm), 0.29±0.13 for _Λ~(12)C and 0.26±0.13 (preliminary) for _Λ~(11)B. This big branching ratio, Γ_(2n)/Γ~(nm), has also been confirmed by the recent reports from FINUDA experiment. These results are quite consistent with those of the theoretical calculations. It seems that the strong contribution of the three-body NMWD is not accidental, but a universal characteristics of NMWD, though the current error bars of the measured values are quite large. The accurate measurement of its branching ratio becomes one of the most urgent issues. Such a big contribution of three-body effect is quite unique so that it provides an excellent means for the numerical studies of three-body interaction models.