αs from τ decays revisited

Being a determination at low energies, the analysis of hadronic τ decay data provides a rather precise determination of the strong coupling αs after evolving the result to MZ. At such a level of precision, even small non-perturbative effects become relevant for the central value and error. While those effects had been taken into account in the framework of the operator product expansion, contributions going beyond it, so-called duality violations, have previously been neglected. The following investigation fills this gap through a finite-energy sum rule analysis of τ decay spectra from the OPAL experiment, including duality violations and performing a consistent fit of all appearing QCD parameters. The resulting values for αs(Mτ) are 0.307(19) in fixed-order perturbation theory and 0.322(26) in contour-improved perturbation theory, which translates to the nf=5 values 0.1169(25) and 0.1187(32) at MZ, respectively.