Revised value for theπ→eνbranching ratio

Abstract

Using the current value for the pion lifetime, we have recomputed the branching ratio for $\pi \to e\nu$ decay obtained from the 1963 experiment of Di Capua et al. and find $\frac{\Gamma (\pi \to e\nu +\pi \to e\nu \gamma )}{\Gamma (\pi \to \mu \nu })=(1.274\mathrm{}\pm 0.024)\times {10}^{-4\mathrm{}}$, a change of 2%. The theoretically predicted value lies within two standard deviations, compared to the ½ standard deviation reported previously.