Decay Measurements in Emulsion on Particles of Negative Strangeness

We report the results of our program of measurement on decay processes of $K^{-}$ mesons, $\Lambda$ hyperons, and charged $\Sigma$ hyperons. Experimental and analytical techniques are outlined. The abundances of the $K^{-}$-meson decay modes were found to be ${K_{\mu 2}}^{-}(56.5\mathrm{}\pm 7.3\%)$, ${K_{\mu 3}}^{-}(9.5\mathrm{}\pm 4.3\%)$, ${K_{\pi 2}}^{-}(26.3\mathrm{}\pm 6.6\%)$, ${\tau }^{-}\mathrm{}(0+2.1\%)\mathrm{}$, ${\tau }^{\prime -}(2.8\mathrm{}\pm 2.4\%)$, and ${K_{e3\mathrm{}}}^{-}(4.9\mathrm{}\pm 3.2\%)$. The mean life of the $K^{-}$ meson is (${1.25}_{-0.17\mathrm{}}^{+0.22\mathrm{}}$)×${10}^{-8\mathrm{}}$ sec. Measurements on 116 $\Lambda$-hyperon decay events in two emulsion stacks determined the $\Lambda$-hyperon mass to be 1115.36±0.14 Mev, using 938.213 Mev and 139.59±0.05 Mev for the proton and pion masses. The $Q$ value derived from these masses is 37.56±0.13 Mev. In an analysis of about 200 hyperfragment decays, no leptonic modes of bound $\Lambda$ hyperons were observed. Some 390 charged $\Sigma$-hyperon decay events were studied. The proton range from the mode ${\Sigma }^{+}\to p+{\pi }^0$ is 1677.5±3.2 μ, corresponding to a momentum of 189.01±0.20 Mev/c. The mass of the ${\Sigma }^{+}$ hyperon from this measurement is 1189.33±0.22 Mev. From the decay mode ${\Sigma }^{+}\to n+{\pi }^{+}$, the ${\pi }^{+}$ range is 92.48±0.49 mm, corresponding to a momentum of 184.44±0.55 Mev/c, and a ${\Sigma }^{+}$ mass of 1188.75±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±1.0 Mev for it, consistent with the ${\pi }^0$ mass of 135.0±0.05 Mev. Studies of the hyperon mean-lives gave, for the ${\Sigma }^{+}$ hyperon, (${0.82}_{-0.08\mathrm{}}^{+0.10\mathrm{}}$)×