αs from an improved τ vector isovector spectral function

Abstract

After discussing difficulties in determining αs from tau decay due to the existence of Duality Violations and the associated asymptotic nature of the OPE, we describe a new determination based on an improved vector isovector spectral function, now based solely on experimental input, obtained by (i) combining ALEPH and OPAL results for 2π + 4π and (ii) replacing K−K0 and higher-multiplicity exclusive-mode contributions, both previously estimated using Monte Carlo, with new experimental BaBar results for K−K0 and results implied by e+e− cross sections and CVC for the higher-multiplicity modes. We find αs(mτ) = 0.3077±0.0075, which corresponds to αs(mZ) = 0.1171±0.0010. Finally, we comment on some of the shortcomings in the criticism of our approach by Pich and Rodriguez-Sanchez.