Leptonic decays of theΣ−andΞ−hyperons

The decays ${\Sigma }^{-}\to n{e}^{-}\overline{\nu }$, ${\Sigma }^{-}\to \Lambda e^{-}\overline{\nu }$ ($\Lambda \to {\pi }^{-}p$), and ${\Xi }^{-}\to \Lambda e^{-}\overline{\nu }$ ($\Lambda \to {\pi }^{-}p$) were studied using unpolarized hyperons from the Yale-Fermilab-BNL hyperon beam at the Brookhaven National Laboratory Alernating Gradient Synchrotron. The ${\Sigma }^{-}$, ${\Xi }^{-}$, $e^{-}$, and $\Lambda$-decay-product momenta were measured by magnetic spectrometers with magnetostrictive wire spark chambers. A threshold C̆erenkov counter and a total absorption calorimeter identified the electron and neutron, respectively. From a sample of 3507 reconstructed ${\Sigma }^{-}\to n{e}^{-}\overline{\nu }$ events we have found $\left|\frac{g_A}{g_V}\right|=0.435\mathrm{}\pm 0.035$. From a sample of 55 reconstructed ${\Sigma }^{-}\to \Lambda e^{-}\overline{\nu }$ events we have found $\frac{g_V}{g_A}=-0.17\mathrm{}\pm 0.35$ assuming that the conserved vector current hypothesis correctly predicts the weak magnetic form factor. A new one-angle Cabibbo fit gives $f=0.436\mathrm{}\pm 0.010$, $d=0.812\mathrm{}\pm 0.011$, and $\theta =0.232\mathrm{}\pm 0.003$ radian.