A Test of the Standard Model, Using Da$\Phi$ne

Abstract

Both the light hypernucleus ${}_\Lambda {\rm H}^4$ and the nucleus ${\rm He}^4$ have spin 0. The ratio $R$ of the electron to muon rates for the pure Fermi transitions \begin{equation} R=\frac{\Gamma\left({}_\Lambda {\rm H}^4\rightarrow {\rm e}^- + \bar \nu +{\rm He}^4\right)} {\Gamma\left({}_\Lambda {\rm H}^4\rightarrow {\mu}^- + \bar \nu +{\rm He}^4\right)} \end{equation} is a sensitive measure of the presence of a {\em second-class} weak current (to the extent that SU(3) is valid in strong interactions), and hence, is a test of the Standard Model. Rates and sensitivities, using Da$\Phi$ne, the $e^+e^-$ machine under construction at Frascati, are discussed.