Branching Ratios of the Decay ModesΣ±→n+e±+ν

A search was made for examples of the beta-decay mode of the sigma hyperon, ${\Sigma }^{\pm }\to n+e^{\pm }+\nu$, among a large sample of sigmas produced by stopped $K^{-}$ mesons in a propane-freon filled bubble chamber. A total of 23 000 negatively charged sigmas and 17 000 positively charged sigmas were observed which decayed via the charged $\pi$ mode, ${\Sigma }^{\pm }\to n+{\pi }^{\pm }$. An electron track was distinguished from that of a $\pi$ meson by the observation that the track curled up in the chamber, or curved too much, or produced a $\delta$ ray with too high an energy to have been produced by a $\pi$ from a sigma decay. No ${{\Sigma }_{\beta }}^{+}$ decays, which are thought to be forbidden by the $\Delta S=\Delta Q$ rule, were found. A total of 11 ${{\Sigma }_{\beta }}^{-}$ decays were found. The branching ratio for ${{\Sigma }_{\beta }}^{-}$ decay, $\frac{\Gamma ({\Sigma }^{-}\to n+e^{-}+\nu )}{\Gamma ({\Sigma }^{-}\to n+{\pi }^{-})}$, was found to be (${1.0}_{-0.3\mathrm{}}^{+0.4\mathrm{}}$)×${10}^{-3\mathrm{}}$. The upper limit of the ratio of the ${{\Sigma }_{\beta }}^{+}$ decay rate to the ${{\Sigma }_{\beta }}^{-}$ decay rate, $\frac{\Gamma ({\Sigma }^{+}\to n+e^{+}+\nu )}{\Gamma ({\Sigma }^{-}\to n+e^{-}+\nu )}$, determined in this experiment was 0.4.