Improved alphas from Tau Decays
Abstract
We present an update of the measurement of alphas(mtau) 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 alphas(mtau) = 0.344 +- 0.005 +- 0.007, where the first error is experimental and the second theoretical. After evolution, the alphas(MZ) determined from tau data is the most precise one to date, in agreement with the corresponding NNNLO value derived from Z decays.
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