Improved measurement of the $\pi \rightarrow \mbox{e} \nu$ branching ratio

TL;DR

This paper reports a more precise experimental measurement of the pion decay branching ratio to electrons versus muons, confirming the Standard Model prediction and testing lepton universality with high accuracy.

Contribution

The study provides an improved measurement of the pion decay branching ratio, enhancing the precision of tests of electron-muon universality in particle physics.

Findings

Measured $R_{e/}$ as (1.2344 ± 0.0023 (stat) ± 0.0019 (syst)) imes 10^{-4}

Results agree with Standard Model predictions

Tested electron-muon universality at 0.1% level

Abstract

A new measurement of the branching ratio, $R_{e/\mu} =\Gamma (\pi^+ \rightarrow \mbox{e}^+ \nu + \pi^+ \rightarrow \mbox{e}^+ \nu \gamma)/ \Gamma (\pi^+ \rightarrow \mu^+ \nu + \pi^+ \rightarrow \mu^+ \nu \gamma)$, 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 %.