Measurement of the rate for pion beta decay

Abstract

The conserved-vector-current hypothesis, together with measured nuclear beta-decay rates, predicts a value of the rate for the decay ${\ensuremath{\pi}}^{+}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{0}$${e}^{+}$\ensuremath{\nu} of 0.4027\ifmmode\pm\else\textpm\fi{}0.0018 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. Using a decay-in-flight technique we have made the most precise measurement to date of this rate, obtaining the value 0.394\ifmmode\pm\else\textpm\fi{}0.015 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, in good agreement with the prediction. This differs slightly from the value previously reported in W. K. McFarlane et al., Phys. Rev. Lett. 51, 249 (1983).