Disintegration of Hyperfragments. II

Abstract

The systematic study of hyperfragments has been continued. A total of 32 000 cosmic-ray stars, 10 000 6-Bev proton stars, 32 000 3-Bev ${\ensuremath{\pi}}^{\ensuremath{-}}$-meson stars and 206 stars produced by stopped negative $K$ mesons were examined. Twenty hyperfragments were found in the cosmic-ray plates, 7 in the proton plates, 30 in the ${\ensuremath{\pi}}^{\ensuremath{-}}$-meson plates and 11 in the negative $K$-meson plates. The average charge of the hyperfragments is between 4 and 5. The average range of the hyperfragments is about 10 microns. Including previous data from this laboratory, only 2 mesonic decays have been found out of 98 events with $Z$ greater than 2. A total of 7 helium hyperfragments have been observed of which 4 decayed mesonically. Of 4 hydrogen hyperfragments, all decayed with the emission of a ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson. In the following eight cases, it was possible to measure the total energy release in the hyperfragment disintegration, and hence to find the following values (in Mev) for the binding energy of the ${\ensuremath{\Lambda}}^{0}$ particle: $_{\ensuremath{\Lambda}}\mathrm{H}^{3}({B}_{\ensuremath{\Lambda}}=0.6\ifmmode\pm\else\textpm\fi{}0.6)$; $_{\ensuremath{\Lambda}}\mathrm{H}^{3}({B}_{\ensuremath{\Lambda}}=\ensuremath{-}0.5\ifmmode\pm\else\textpm\fi{}0.6)$; $_{\ensuremath{\Lambda}}\mathrm{H}^{3}({B}_{\ensuremath{\Lambda}}=0.4\ifmmode\pm\else\textpm\fi{}0.7)$; $_{\ensuremath{\Lambda}}\mathrm{H}^{4}({B}_{\ensuremath{\Lambda}}=0.5\ifmmode\pm\else\textpm\fi{}2.0 or 1.9\ifmmode\pm\else\textpm\fi{}2.0)$; $_{\ensuremath{\Lambda}}\mathrm{He}^{4}({B}_{\ensuremath{\Lambda}}=0.0\ifmmode\pm\else\textpm\fi{}2.0)$; $_{\ensuremath{\Lambda}}\mathrm{He}^{4}({B}_{\ensuremath{\Lambda}}=1.8\ifmmode\pm\else\textpm\fi{}0.6)$; $_{\ensuremath{\Lambda}}\mathrm{He}^{5}({B}_{\ensuremath{\Lambda}}=2.0\ifmmode\pm\else\textpm\fi{}0.6)$; $_{\ensuremath{\Lambda}}\mathrm{Be}^{9}({B}_{\ensuremath{\Lambda}}=6.5\ifmmode\pm\else\textpm\fi{}0.6)$. The binding energies tend to increase with increasing mass number. The fact that $_{\ensuremath{\Lambda}}\mathrm{H}^{4}$ and $_{\ensuremath{\Lambda}}\mathrm{He}^{5}$ hyperfragments exist, plus the fact that the binding energy of the ${\ensuremath{\Lambda}}^{0}$ particle in $_{\ensuremath{\Lambda}}\mathrm{Be}^{9}$ is greater than that of the last neutron in ${\mathrm{Be}}^{9}$, shows that the Pauli principle need not be considered for a ${\ensuremath{\Lambda}}^{0}$ particle bound in a nucleus. If the binding of the ${\ensuremath{\Lambda}}^{0}$ particle can be described in terms of a potential well the depth of the well is greater than 6.5 Mev, as indicated by ${B}_{\ensuremath{\Lambda}}$ for $_{\ensuremath{\Lambda}}\mathrm{Be}^{9}$. In light hyperfragments the low binding energies imply that the ${\ensuremath{\Lambda}}^{0}$ particle spends much of its time outside the nucleus. The momentum of the ${\ensuremath{\Lambda}}^{0}$ particle has been measured in several light hyperfragments where a ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson and proton were emitted, by assuming it to be equal to the momentum of the ${\ensuremath{\pi}}^{\ensuremath{-}}$ meson and proton. In general the momentum values are quite low, which supports the hypothesis that the bound ${\ensuremath{\Lambda}}^{0}$ particle spends considerable time outside the nucleus. No further examples of energetic hyperfragments, as have been previously reported, were found in this work.