Hypernuclear weak decay experiments at KEK; nucleon inclusive measurement Original Research Article

Recent high quality neutron spectrum of 12ΛC made it possible to derive the Γn/Γp ratio directly comparing its yield to that of the previous proton spectrum. The derived ratio, (0.45–0.51)±0.15, was significantly smaller than unity showing the dominance of the proton induced NMWD channel for the first time and agreed well with the recent theoretical calculations. However, this ratio still has inherent ambiguity due to the two nucleon induced NMWD and the nuclear final state interaction (FSI). Recently exclusive coincidence measurements of each NMWD channel of 5ΛHe and 12ΛC were made in order to reduce such ambiguities and confirmed the proton channel dominance in both inclusive and exclusive data. Important progress also has been made in the measurement of the decay asymmetry parameter, View the MathML source, of the NMWD of 5ΛHe and 12ΛC with much improved statistics over previous experiments. We have obtained small View the MathML source values for both 5ΛHe and 12ΛC, close to zero within one a sigma level. The nearly identical View the MathML source values of 5ΛHe and 12ΛC indicates that the NMWD mechanisms of s- and p-shell hypernuclei are similar. However, the theoretical results for View the MathML sourcein the range of −0.6–(−0.7). Though these new results seem to indicate that the long standing inconsistency between the Γn/Γp values of experiments and theories has almost been resolved, the decay asymmetry still remains to be understood.