Measurement of the Branching Ratio for the DecayK+→e++ν

The decay rate for the mode $K^{+}\to e^{+}+\nu$ has been measured. There are ten events, which include an estimated 0.34 background event only, and the branching ratio relative to $K^{+}\to {\mu }^{+}+\nu$ is found to be $R={1.9}_{-0.5\mathrm{}}^{+0.8\mathrm{}}\times {10}^{-5\mathrm{}}$. This is in good agreement with the prediction of the $V-A$ theory, which is $R=2.10\mathrm{}\times {10}^{-5\mathrm{}}$, including radiative corrections.