We have scanned 550 000 pictures of stopping $K^{-}$ mesons in hydrogen for the decays ${\Sigma }^{\pm }\to \Lambda +e^{\pm }+\nu$, and find ${\Sigma }^{-}\to \Lambda +e^{-}+\nu /\mathrm{all}$ ${\Sigma }^{-}$ decays to be (0.64±0.12)×${10}^{-4\mathrm{}}$ and ${\Sigma }^{+}\to \Lambda +e^{+}\nu /\mathrm{all}$ ${\Sigma }^{+}$ decays to be (0.20±0.08)×${10}^{-4\mathrm{}}$. The rate for ${\Sigma }^{-}\to \Lambda +e^{-}+\nu$ yields a value of $D=0.76\mathrm{}\pm 0.07$, and $\alpha =\frac{D}{\mathrm{}(D+F)\mathrm{}}=0.64\mathrm{}\pm 0.06$. The observed electron-neutrino angular correlation together with the lambda polarization determines the magnitude of the ratio of vector to axial-vector coupling for this decay to be 0.31±0.30, consistent with the hypothesis of conserved vector current, with the absence of second-class currents, and with time-reversal invariance.

• Received 29 May 1967

DOI:https://doi.org/10.1103/PhysRevLett.19.181