Improved Measurement of the π→eν Branching Ratio

Phys Rev Lett. 2015 Aug 14;115(7):071801. doi: 10.1103/PhysRevLett.115.071801. Epub 2015 Aug 13.

Abstract

A new measurement of the branching ratio R_{e/μ}=Γ(π^{+}→e^{+}ν+π^{+}→e^{+}νγ)/Γ(π^{+}→μ^{+}ν+π^{+}→μ^{+}νγ) resulted in R_{e/μ}^{exp}=[1.2344±0.0023(stat)±0.0019(syst)]×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%.