Decay Measurements in Emulsion on Particles of Negative Strangeness

Abstract

We report the results of our program of measurement on decay processes of ${K}^{\ensuremath{-}}$ mesons, $\ensuremath{\Lambda}$ hyperons, and charged $\ensuremath{\Sigma}$ hyperons. Experimental and analytical techniques are outlined. The abundances of the ${K}^{\ensuremath{-}}$-meson decay modes were found to be ${{K}_{\ensuremath{\mu}2}}^{\ensuremath{-}}(56.5\ifmmode\pm\else\textpm\fi{}7.3%)$, ${{K}_{\ensuremath{\mu}3}}^{\ensuremath{-}}(9.5\ifmmode\pm\else\textpm\fi{}4.3%)$, ${{K}_{\ensuremath{\pi}2}}^{\ensuremath{-}}(26.3\ifmmode\pm\else\textpm\fi{}6.6%)$, ${\ensuremath{\tau}}^{\ensuremath{-}}(0+2.1%)$, ${\ensuremath{\tau}}^{\ensuremath{'}\ensuremath{-}}(2.8\ifmmode\pm\else\textpm\fi{}2.4%)$, and ${{K}_{e3}}^{\ensuremath{-}}(4.9\ifmmode\pm\else\textpm\fi{}3.2%)$. The mean life of the ${K}^{\ensuremath{-}}$ meson is (${1.25}_{\ensuremath{-}0.17}^{+0.22}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ sec. Measurements on 116 $\ensuremath{\Lambda}$-hyperon decay events in two emulsion stacks determined the $\ensuremath{\Lambda}$-hyperon mass to be 1115.36\ifmmode\pm\else\textpm\fi{}0.14 Mev, using 938.213 Mev and 139.59\ifmmode\pm\else\textpm\fi{}0.05 Mev for the proton and pion masses. The $Q$ value derived from these masses is 37.56\ifmmode\pm\else\textpm\fi{}0.13 Mev. In an analysis of about 200 hyperfragment decays, no leptonic modes of bound $\ensuremath{\Lambda}$ hyperons were observed. Some 390 charged $\ensuremath{\Sigma}$-hyperon decay events were studied. The proton range from the mode ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p+{\ensuremath{\pi}}^{0}$ is 1677.5\ifmmode\pm\else\textpm\fi{}3.2 \ensuremath{\mu}, corresponding to a momentum of 189.01\ifmmode\pm\else\textpm\fi{}0.20 Mev/c. The mass of the ${\ensuremath{\Sigma}}^{+}$ hyperon from this measurement is 1189.33\ifmmode\pm\else\textpm\fi{}0.22 Mev. From the decay mode ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}n+{\ensuremath{\pi}}^{+}$, the ${\ensuremath{\pi}}^{+}$ range is 92.48\ifmmode\pm\else\textpm\fi{}0.49 mm, corresponding to a momentum of 184.44\ifmmode\pm\else\textpm\fi{}0.55 Mev/c, and a ${\ensuremath{\Sigma}}^{+}$ mass of 1188.75\ifmmode\pm\else\textpm\fi{}0.54 Mev. If the mass of the neutral particle in the proton decay mode is considered unknown, these measurements imply a mass of 134.0\ifmmode\pm\else\textpm\fi{}1.0 Mev for it, consistent with the ${\ensuremath{\pi}}^{0}$ mass of 135.0\ifmmode\pm\else\textpm\fi{}0.05 Mev. Studies of the hyperon mean-lives gave, for the ${\ensuremath{\Sigma}}^{+}$ hyperon, (${0.82}_{\ensuremath{-}0.08}^{+0.10}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec, and for the ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ hyperon, (${1.75}_{\ensuremath{-}0.30}^{+0.39}$)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec. Reasons for experimental biases that have affected some emulsion measurements are discussed. The branching ratio ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}\frac{(p+{\ensuremath{\pi}}^{0})}{(\mathrm{all} {\ensuremath{\Sigma}}^{+} \mathrm{decay})}$ was found to be 0.50\ifmmode\pm\else\textpm\fi{}0.03. No example of the decay mode ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p+\ensuremath{\gamma}$ was found in a sample of 95 ${\ensuremath{\Sigma}}^{+}\ensuremath{\rightarrow}p$ decay events. No ${\ensuremath{\Sigma}}^{+}$ leptonic decay events were observed among 129 ${\ensuremath{\pi}}^{+}$ decays, nor any ${\ensuremath{\Sigma}}^{\ensuremath{-}}$ leptonic modes among 67 ${\ensuremath{\pi}}^{\ensuremath{-}}$ events. No up-down decay asymmetry was detected in any mode for charged hyperons emitted from complex nuclei in association with a charged pion.