Nonmesonic Decay of Helium Hyperfragments

Approximately 35 000 $K^{-}$ capture stars in an emulsion stack were examined for hyperfragments. A sample of ${\pi }^{-}$-esonic and nonmesonic He hyperfragments was selected for the purpose of estimating the nonmesonic-to-${\pi }^{-}$-mesonic decay ratios for ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}$ and for ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^5{}_{}{}^{}$. The following values were obtained: $Q\left({}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}\right)=1.02\mathrm{}\pm 0.15$, $Q\left({}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^5{}_{}{}^{}\right)=1.21\mathrm{}\pm 0.19$, for the nonmesonic-to-${\pi }^{-}$ mesonic decay ratios of ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}$ and ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^5{}_{}{}^{}$, respectively. Also, an attempt was made to estimate the ratio of proton stimulation to neutron stimulation for the nonmesonic decays of ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}$ and ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^5{}_{}{}^{}$, for various cutoff energies of the observed "fast protons." Furthermore, by combining our data with previous results, we obtained estimates of the nonmesonic and the total decay rates of ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^4{}_{}{}^{}$ and ${}_{\Lambda }{}^{}{}_{}{}^{}\mathrm{He}_{}^5{}_{}{}^{}$.