Study of the Decayπ→e+ν

Abstract

A large NaI(Tl) crystal has been used to measure the $\pi \to \frac{e}{\pi }\to \mu$ branching ratio. From a sample of 10 800 $\pi \to e$ decay electrons the branching ratio was found to be $R=(1.247\mathrm{}\pm 0.028)\times {10}^{-4\mathrm{}}$ in agreement with a universal theory for ($e\nu$) and ($\mu \nu$) weak couplings.