Hypernuclear weak decay of C-12(Lambda) and B-11(Lambda)

The branching ratios of negative pions and protons due to the weak decays of C-12(Lambda) and B-11(Lambda) hypernuclei were measured. The negative pionic decay rates (Gamma(pi-)), proton-induced nonmesonic decay rates (Gamma(p)), total nonmesonic decay rates (Gamma(nm), and ratios of the Lambda n-->nn process to the Lambda p-->pn process (Gamma(n)/Gamma(p)) were derived from the present measurements combined with previous studies on the mesonic pi(0) and total decay rates. The measured Gamma(pi-) shows that Pauli blocking is less effective than expected due to pion distortion. We found that Gamma(nm) is nearly equal to unity in units of the free-space Lambda-decay width. The present results also indicate that Gamma(n) is almost twice that of Gamma(p). This is in disagreement with calculations based on meson-exchange models in which Gamma(n) is strongly suppressed.