|V_us| from Strange Hadronic Tau Data

Abstract

We report on recent work to determine the CKM matrix element |V_{us}| using strange hadronic \tau decay data. We use the recent OPAL update of the strange spectral function, while on the theory side we update the dimension-two perturbative contribution including the recently calculated \alpha_s^3 terms. Our result |V_{us}|=0.2220 \pm 0.0033 is already competitive with the standard extraction from K_{e3} decays and other new proposals to determine |V_{us}|. The actual uncertainty on |V_{us}| from \tau data is dominated largely by experiment and will eventually be much reduced by B-factories and future \tau-charm factory data, providing one of the most accurate determinations of this Standard Model parameter.