Weak Decay of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">C</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow><mml:mi>Λ</mml:mi></mml:mrow><mml:mrow><mml:mn>12</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">B</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow><mml:mi>Λ</mml:mi></mml:mrow><mml:mrow><mml:mn>11</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>Hypernuclei

A measurement is reported of the mean lifetime, $\ensuremath{\tau}$, for the weak decay of $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ and $_{\ensuremath{\Lambda}}^{11}\mathrm{B}$ hypernuclei. The experiment detected energetic protons from the hypernuclear nonmesonic decay $\ensuremath{\Lambda}+p\ensuremath{\rightarrow}n+p$, in coincidence with hypernuclear production by the strangeness-changing reactions $^{12}\mathrm{C}({K}^{\ensuremath{-}}, {\ensuremath{\pi}}^{\ensuremath{-}})_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ and $^{12}\mathrm{C}({K}^{\ensuremath{-}}, {\ensuremath{\pi}}^{\ensuremath{-}})p, _{\ensuremath{\Lambda}}^{11}\mathrm{B}$. The measured ground-state decay lifetimes $\ensuremath{\tau}(_{\ensuremath{\Lambda}}^{12}\mathrm{C})=(2.11\ifmmode\pm\else\textpm\fi{}0.31)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec and $\ensuremath{\tau}(_{\ensuremath{\Lambda}}^{11}\mathrm{B})=(1.92\ifmmode\pm\else\textpm\fi{}0.22)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ sec are compared with $\ensuremath{\Lambda}N$ weak-interaction calculations.