Eur. Phys. J. C (2004) 35: 53-65
https://doi.org/10.1140/epjc/s2004-01745-1

theoretical physics

K _e3 decays and CKM unitarity

¹ Departament de Física Teórica, IFIC, Universitat de Valéncia - CSIC, Apt. Correus 22085, 46071, Valéncia, Spain
² Department of Physics, California Institute of Technology, 91125, Pasadena, California, USA
³ Institut für Theoretische Physik, Universität Wien, Boltzmanngasse 5, 1090, Wien, Austria
⁴ Paul Scherrer Institut, 5232, Villigen PSI, Switzerland

Abstract

We present a detailed numerical study of the K _e3 decays to in chiral perturbation theory with virtual photons and leptons. We describe the extraction of the CKM matrix element |V _us | from the experimental K _e3 decay parameters. We propose a consistency check of the K ⁺ _e3 and K ⁰ _e3 data that is largely insensitive to the dominating theoretical uncertainties, in particular the contributions of . Our analysis is highly relevant in view of the recent high statistics measurement of the K ⁺ _e3 branching ratio by E865 at Brookhaven which does not indicate any significant deviation from CKM unitarity but rather a discrepancy with the present K ⁰ _e3 data.