Hypernuclear weak decay ofCΛ12andBΛ11

The branching ratios of negative pions and protons due to the weak decays of ${}_{\Lambda }{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{\Lambda }{}^{11}{}_{}{}^{}\mathrm{B}$ hypernuclei were measured. The negative pionic decay rates (${\Gamma }_{{\pi }^{-}}$), proton-induced nonmesonic decay rates (${\Gamma }_p$), total nonmesonic decay rates (${\Gamma }_{\mathrm{nm}}$), and ratios of the $\Lambda n\to \mathrm{nn}$ process to the $\Lambda p\to \mathrm{pn}$ process ($\frac{{\Gamma }_n}{{\Gamma }_p}$) 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 ${\Gamma }_{\mathrm{nm}}$ 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.