Decay Parameters forΣ±→nπ±

In this paper, we present measurements of the decay parameters ${\psi }_{\pm }$ for ${\Sigma }^{\pm }\to n{\pi }^{\pm }$. The usual decay parameters $\alpha$, $\beta$, and $\gamma$ are related to $\phi$ by the equation $\beta ={(1-{\alpha }^2)}^{\frac{1}{2}}sin\phi$ and $\gamma ={(1-{\alpha }^2)}^{\frac{1}{2}}cos\phi$. Polarized ${\Sigma }^{\pm }$ were produced by the reactions $K^{-}p\to {\Sigma }^{\pm }{\pi }^{\mp }$ in the Lawrence Radiation Laboratory's 25-in. hydrogen bubble chamber. The average momentum of the incident $K^{-}$ beam was 385 MeV/c. The measurements of ${\phi }_{\pm }$ were made by observing the left-right asymmetry in the $\mathrm{np}$ interactions of those decay neutrons that subsequently scattered on the hydrogen in the bubble chamber. We obtain ${\phi }_{-}=14\mathrm{}\pm 19$ deg and ${\phi }_{+}=143\mathrm{}\pm 29$ deg. Since $\gamma =\frac{({\mathrm{}\left|s\right|\mathrm{}}^2-{\mathrm{}\left|p\right|\mathrm{}}^2)}{({\mathrm{}\left|s\right|\mathrm{}}^2+{\mathrm{}\left|p\right|\mathrm{}}^2)}$, this shows that ${\Sigma }^{-}\to n{\pi }^{-}$ takes place predominantly in the $s$ wave, whereas ${\Sigma }^{+}\to n{\pi }^{+}$ is dominated by $p$-wave decay. These results are in agreement with the $\Delta l=\frac{1}{2}$ rule.