Measurement of the ${\pi }^{+}\to e^{+}\nu$ branching ratio

A measurement of the ${\pi }^{+}\to e^{+}\nu$ branching ratio gives $R_{\pi e\nu }=\frac{\Gamma (\pi \to e\nu +\pi \to e\nu \gamma )}{\Gamma (\pi \to \mu \nu +\pi \to \mu \nu \gamma )}=1.2265\mathrm{} \pm 0.0034\left(\mathrm{stat}\right) \pm 0.0044\left(\mathrm{sys}\right) \times {10}^{-4\mathrm{}}$. This result is in agreement with standard model calculations and confirms the hypothesis of electron-muon universality at the 0.2% level.