Improved alpha_s from Tau Decays

Abstract

We present an update of the measurement of alpha_s(m_tau) from ALEPH tau hadronic spectral functions. We report a study of the perturbative prediction(s) showing that the fixed-order perturbation theory manifests convergence 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 alpha_s(m_tau) = 0.344 +- 0.005 +- 0.007, where the first error is experimental and the second theoretical. After evolution, the alpha_s(M_Z) determined from tau data is the most precise one to date, in agreement with the corresponding NNNLO value derived from Z decays.Comment: 4pages, 1 figure, Contribution to the proceedings of Moriond 2008, QCD sessio