Search for new Physics with the $\pi \to e\nu$ Decay

Abstract

In the Standard Model, lepton universality refers to the identical electroweak gauge interactions among charged leptons. The measurement of the branching ratio $R_{e/\mu }=\frac{\Gamma (\pi \to e\nu )}{\Gamma (\pi \to \mu \nu )}$ is one of the most stringent tests of lepton universality between the first two generations. The TRIUMF PIENU experiment aims at the most precise test of universality measuring $R_{e/\mu }$ with 0.1% precision. The measurement will provide improved constraints to physics beyond the Standard Model or uncover new scenarios if a disagreement is found.