Leptonic Pion Decay And Physics Beyond The Electroweak Standard Model

Bruce A. Campbell, Ahmed Ismail

The ratio of branching ratios in leptonic pion decay $R_{\pi }\equiv (\Gamma ({\pi }^{-}\to e{\nu }_e))/(\Gamma ({\pi }^{-}\to \mu {\nu }_{\mu }))$ is a powerfully sensitive probe of new interactions beyond the electroweak st…