New determination of αs from hadronic τ decays

Abstract

We present a new framework for the extraction of the strong coupling from hadronic τ decays through finite-energy sum rules. Our focus is on the small, but still significant nonperturbative effects that, in principle, affect both the central value and the systematic error. We employ a quantitative model in order to accommodate violations of quark-hadron duality, and enforce a consistent treatment of the higher-dimensional contributions of the operator product expansion to our sum rules. Using 1998 OPAL data for the nonstrange isovector vector and axial-vector spectral functions, we find the n(sub)f=3 values α(sub)s(m(sub)τ²)=0.307±0.019 in fixed-order perturbation theory, and 0.322±0.026 in contour-improved perturbation theory. For comparison, the original OPAL analysis of the same data led to the values 0.324±0.014 (fixed order) and 0.348±0.021 (contour improved).