Updated determination of αs from τ decays

Abstract

Employing our previous framework to treat nonperturbative effects self-consistently, including duality violations, we update the determination of the strong coupling, αs, using a modified version of the 1998 OPAL data, updated to reflect current values of exclusive-mode hadronic τ-decay branching fractions. Our best nf=3 values from the updated OPAL data are αs(mτ2)=0.325±0.018 and αs(mτ2)=0.347±0.025 in fixed-order and contour-improved perturbation theory, respectively. To account for nonperturbative effects, nonlinear, multiparameter fits are necessary. We have, therefore, investigated the posterior probability distribution of the model parameters underlying our fits in more detail. We find that OPAL data alone provide only weak constraints on some of the parameters needed to model duality violations, especially in the case of fits involving axial-vector channel data, making additional prior assumptions on the expected size of these parameters necessary at present. We provide evidence that this situation could be greatly improved if hadronic spectral functions based on the high-statistics BABAR and Belle data were to be made available.