Precise αS Determination from τ Decays

An updated measurement of from ALEPH τ hadronic spectral functions is presented. We report a study of the perturbative prediction(s) showing that the fixed-order perturbation theory manifests convergence or principle problems not presented in the contour-improved calculation. Potential systematic effects from quark-hadron duality violations are estimated to be within the quoted systematic errors. The fit result is , where the first error is experimental and the second theoretical. After evolution, the determined from τ data is one of the most precise to date, in agreement with the corresponding N3LO value derived from Z decays.