Measurement of $\Gamma(K_{\mu 3})/\Gamma(K_{e3})$ ratio using stopped positive kaons

Abstract

The ratio of the $K^{+}\to \pi^{0} \mu^{+} \nu$ ($K_{\mu3}^+$) and $K^{+}\to \pi^{0} e^{+} \nu$ ($K_{e3}^+$) decay widths, $\Gamma(K_{\mu 3})/\Gamma(K_{e3})$, has been measured with stopped positive kaons. $K_{\mu3}^+$ and $K_{e3}^+$ samples containing 2.4$\times 10^4$ and 4.0$\times 10^4$ events, respectively, were analyzed. The $\Gamma(K_{\mu3})/\Gamma(K_{e3})$ ratio was obtained to be 0.671$\pm$0.007(stat.)$\pm$0.008(syst.) calculating the detector acceptance by a Monte Carlo simulation with the assumption of $\mu$-$e$ universality in $K_{l3}^+$ decay. The coefficient of the $q^2$ dependent term of the $f_0$ form factor was also determined to be $\lambda_0$=0.022$\pm$0.005(stat.)$\pm$0.004(syst.).