Improved measurement of the $π\rightarrow \mbox{e} ν$ branching ratio

Abstract

A new measurement of the branching ratio, $R_{e/μ} =Γ(π^+ \rightarrow \mbox{e}^+ ν+ π^+ \rightarrow \mbox{e}^+ νγ)/ Γ(π^+ \rightarrow μ^+ ν+ π^+ \rightarrow μ^+ νγ)$, resulted in $R_{e/\mu }^{exp}=(1.2344\pm 0.0023(stat)\pm 0.0019(syst))\times 10^{-4}$. This is in agreement with the standard model prediction and improves the test of electron-muon universality to the level of 0.1 %.

5 pages, 4 figures