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

V. I. Romanovsky, S. A. Akimenko, G. I. Britvich, K. V. Datsko, A. P. Filin, A. V. Inyakin, A. S. Konstantinov, I. Y. Korolkov, V. A. Khmelnikov, V. M. Leontiev, V. P. Novikov, V. F. Obraztsov, V. A. Polyakov, V. I. Shelikhov, O. G. Tchikilev, V. A. Uvarov, O. P. Yushchenko, V. N. Bolotov, V. A. Duk, S. V. Laptev, A. Yu. Polyarush

Published 2007-04-16, updated 2007-05-22Version 2

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 $Br_{K_{e3}}= (5.124 \pm 0.009 (stat) \pm 0.029(norm) \pm 0.030(syst))%$. 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.