An updated determination of \alpha_s from tau decays

TL;DR

This paper refines the measurement of the strong coupling constant _s from tau decay data by incorporating non-perturbative effects and duality violations, using updated experimental data and advanced statistical analysis.

Contribution

It introduces a self-consistent framework for including non-perturbative effects in _s determination and analyzes the impact of data constraints on model parameters.

Findings

_s(m^2_)=0.325b10.018 from fixed-order perturbation theory

_s(m^2_)=0.347b10.025 from contour-improved perturbation theory

Weak constraints on duality violation parameters from OPAL data, especially in axial vector channel

Abstract

Employing our previous framework to treat non-perturbative effects self-consistently, including duality violations, we update the determination of the strong coupling, \alpha_s, using a modified version of the 1998 OPAL data, updated to reflect current values of exclusive mode hadronic \tau decay branching fractions. Our best n_f=3 values from the updated OPAL data are \alpha_s(m^2_\tau)=0.325+-0.018 and \alpha_s(m^2_\tau)=0.347+-0.025 in fixed-order and contour-improved perturbation theory, respectively. To account for non-perturbative effects, non-linear, multi-parameter 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.