Precise tests of e-μ universality

In this paper, the status of experimental tests of electron-muon universality in weak interactions is reviewed. The average of the new mesurements of the π+ → e+ν branching ratio, Rave = Γ(π) → ev + π → ev(γ)/Γ(π) → μν + → μνγ = (1.2312 ± 0.00037) x 10 -4, is consistent with standard model calculations Rth = (1,234 ± 0.0001) x 10-4 and confirms the hypothesis of electron-muon universality at the 0.2% level