Kl3+Decay Rates

Abstract

An experiment has been performed at the Brookhaven Cosmotron to study ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{l}^{+}\ensuremath{\nu}$. A spark-chamber-magnet system was triggered on any charged particle leaving the target after a ${K}^{+}$ had stopped. Separation between ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\mu}}^{+}$ was performed using momentum and range. Positrons were identified by shower production. On the basis of 300 ${K}_{e3}$ and 350 ${K}_{\ensuremath{\mu}3}$ events in the momentum range 100 to 220 MeV/c, we found ratios $\frac{{K}_{e3}}{(\mathrm{all} {K}^{+})}=0.044\ifmmode\pm\else\textpm\fi{}0.004$, $\frac{{K}_{\ensuremath{\mu}3}}{(\mathrm{all} {K}^{+})}=0.035\ifmmode\pm\else\textpm\fi{}0.0030$. The positron spectrum was consistent with a constant form factor. The ratio of constant form factors $\ensuremath{\xi}=\frac{{f}_{\ensuremath{-}}}{{f}_{+}}$ determined from the $\frac{{K}_{e3}}{{K}_{\ensuremath{\mu}3}}$ branching ratio was $\ensuremath{\xi}=+1.0\ifmmode\pm\else\textpm\fi{}0.3$.