Ke3 decays and CKM unitarity

Abstract.We present a detailed numerical study of the Ke3 decays to ${\cal O}(p^6, (m_d-m_u)p^2, e^2 p^2)$ in chiral perturbation theory with virtual photons and leptons. We describe the extraction of the CKM matrix element |Vus| from the experimental Ke3 decay parameters. We propose a consistency check of the K + e3 and K0e3 data that is largely insensitive to the dominating theoretical uncertainties, in particular the contributions of ${\cal O}(p^6)$. 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 K0e3 data.