Measurement of K^{-}_{e3} branching ratio

Abstract

The branching fraction for the decay $K^{-}\to {\pi }^{0}e\bar{\nu }$ is measured using in-flight decays detected with {\bf ISTRA+} setup working at the 25 GeV negative secondary beam of the U-70 PS:\linebreak $B{r}_{K_{e3}}=(5.124\pm 0.009(stat)\pm 0.029(norm)\pm 0.030(syst))$. From this value the $|V_{us}|$ element of the CKM matrix is extracted, using previously measured $f_{+}(t)$ form factor: $|V_{us}|=0.227\pm 0.002$. The results are in agreement with recent measurements by BNL E865, FNAL KTeV, KLOE.

10 pages, 8 figures