A novel route to V_us

Abstract

Already in the past, hadronic tau decays have served as an interesting source to obtain information on the parameters of the Standard Model, like the strong coupling alpha_s or the strange quark mass. Below it will be shown that the approach to obtain the strange mass from the hadronic tau-decay width can be turned into a determination of the CKM matrix element V_us, once the strange mass is used as an input from other sources. At present, we obtain V_us = 0.2179 +- 0.0045, where the error is completely dominated by the experimental uncertainty, and can be improved through an improved measurement of the hadronic tau-decay rate into strange particles R_tau,S.