V_us From Hadronic Tau Decays

Abstract

We study extractions of |V_us| based on finite energy sum rule (FESR) analyses of hadronic tau decay data. We show (i) that the ``(0,0) spectral weight'' implementation (proposed previously in the literature as a favorable version of this analysis) suffers from significant convergence problems, but (ii) that alternate implementations exist which bring these problems under control. Results based on present spectral data are shown to be in agreement with those of other approaches, though with, at present, somewhat larger experimental errors. Sub-1% determinations of |V_us| are also shown to be expected from these alternate analyses once tau data from the B factories becomes available.