Precision Measurement of the $\pi$$^+$$\rightarrow$$e^+$$\nu$$_e$ Branching Ratio in the PIENU Experiment

Abstract

The PIENU experiment at TRIUMF aims to measure the branching ratio of the pion decay modes $R^{\pi}=[{\pi}^+{\rightarrow}e^+{\nu}_e({\gamma})]/[{\pi}^+{\rightarrow}{\mu}^+{\nu}_{\mu}({\gamma})]$ with precision of $<0.1\%$. Precise measurement of $R^{\pi}$ provides a stringent test of electron-muon universality in weak interactions. The current status of the PIENU experiment and future prospects are presented.