Leptonic Decays of ChargedΣHyperons and theΔS=ΔQSelection Rule

Abstract

Leptonic decays of ${\Sigma }^{+}$ and ${\Sigma }^{-}$ hyperons have been searched for in a sample of about 500 000 ${\Sigma }^{\pm }$ decays. This report is based on the observation of 130 ${\Sigma }^{\pm }$ leptonic decays of various types. The principal results are: (a) no evidence for $\Delta S=-\Delta Q$ ${\Sigma }^{+}$ leptonic decays, with the upper limit (with 90% confidence) for the ratio of $\Delta Q=-\Delta S$ to $\Delta Q=+\Delta S$ transitions equal to 0.12; (b) $\frac{({\Sigma }^{-}\to \Lambda +e^{-}+y)}{({\Sigma }^{-}\to n+{\pi }^{-})}=(0.75\mathrm{}\pm 0.28)\times {10}^{-4\mathrm{}}$; (c) $\frac{({\Sigma }^{-}\to n+e^{-}+\nu )}{({\Sigma }^{-}\to n+{\pi }^{-})}=1.4\mathrm{}\pm 0.3\times {10}^{-3\mathrm{}}$; and (d) $\frac{({\Sigma }^{-}\to n+{\mu }^{-}+\nu )}{({\Sigma }^{-}\to n+{\pi }^{-})}=0.66\mathrm{}\pm 0.14\times {10}^{-3\mathrm{}}$. The data are consistent with ($\mu \nu$), ($e\nu$) universality for ${\Sigma }^{-}\to n+l^{-}+\nu$ decays and with the $\Delta I=1\mathrm{}$ rule for ${\Sigma }^{\pm }\to \Lambda +e^{\pm }+\nu$ decays. A comparison is made between experiment and Cabibbo's theory of weak interactions. Acceptable agreement is found for Cabibbo's angle $\theta$ close to 0.26 and with the axial-vector ($\frac{F}{D}$) ratio approximately equal to ½ or 2.