alpha_s from tau decays revisited

TL;DR

This paper refines the determination of the strong coupling constant alpha_s from tau decay data by including duality violations in the analysis, leading to more accurate and reliable results.

Contribution

It introduces a finite-energy sum rule analysis that accounts for duality violations, improving the precision of alpha_s extraction from tau decay spectra.

Findings

Alpha_s(M_tau) = 0.307(19) in fixed-order perturbation theory

Alpha_s(M_tau) = 0.322(26) in contour-improved perturbation theory

Corresponding alpha_s(M_Z) values are 0.1169(25) and 0.1187(32)

Abstract

Being a determination at low energies, the analysis of hadronic tau decay data provides a rather precise determination of the strong coupling alpha_s after evolving the result to M_Z. 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 tau decay spectra from the OPAL experiment, including duality violations and performing a consistent fit of all appearing QCD parameters. The resulting values for alpha_s(M_tau) are 0.307(19) in fixed-order perturbation theory and 0.322(26) in contour-improved perturbation theory, which translates to the n_f=5 values 0.1169(25) and 0.1187(32) at M_Z, respectively.