Theoretical progress on the Vus determination from tau decays
Abstract
A very precise determination of Vus can be obtained from the semi-inclusive hadronic decay width of the tau lepton into final states with strangeness. The ratio of the Cabibbo-suppressed and Cabibbo-allowed tau decay widths directly measures (Vus/Vud)2, up to very small SU(3)-breaking corrections which can be theoretically estimated with the needed accuracy. Together with previous LEP and CLEO data, the recent measurements by Babar and Belle of some Cabibbo-suppressed tau decays imply Vus= 0.2165 +- 0.0026exp +- 0.0005th, which is already competitive with the standard extraction from Kl3 decays. The uncertainty is largely dominated by experimental errors and should be easily reduced with the high statistics of the B factories, providing the most accurate determination of this parameter. A 1% experimental precision on the Cabibbo-suppressed tau decay width would translate into a 0.6% uncertainty on Vus.