Measurement of Pion Beta-Decay Branching Ratio

The branching ratio for pion beta decay, $R=\frac{({\pi }^{+}\to {\pi }^0+e^{+}+\nu )}{({\pi }^{+}\to {\mu }^{+}+\nu )}$, was measured. Arrays of lead sheets, scintillators, and spark chambers were used to measure the angular distribution of the $\gamma$ rays in delayed coincidence with stopping pions. Thirty-eight events remained after subtraction of a background of eight, leading to a branching ratio of (1.07±0.21)×${10}^{-8\mathrm{}}$. This result is in good agreement with conserved vector-current theory and with the results of other experiments.