A new determination of α_s from hadronic τ decays

We present a new framework for the extraction of the strong coupling from hadronic τdecays through finite-energy sum rules. Our focus is on the small, but still significant non-perturbative 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 non-strange isovector vector and axial-vector spectral functions, we find the n_f=3 values α_s(m_τ^2)=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).

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