Modified Contour-Improved Perturbation Theory

TL;DR

This paper introduces a modified contour-improved perturbation theory for analyzing tau decay data, reducing ambiguities and scale dependence, leading to a more precise determination of the strong coupling constant.

Contribution

The authors propose a derivative expansion-based modification to the standard contour-improved method, improving stability and reducing uncertainties in QCD coupling extraction.

Findings

Renormalization scale dependence is reduced by over a factor of two.

The extracted alpha_s(M_Z^2) is 0.1211 ± 0.0010.

The modification lowers the coupling value by 2% compared to the standard method.

Abstract

The semihadronic tau decay width allows a clean extraction of the strong coupling constant at low energies. We present a modification of the standard "contour improved" method based on a derivative expansion of the Adler function. The approach eliminates ambiguities coming from the existence of different integral expressions for the semihadronic tau decay ratio. Compared to the standard method, renormalization scale dependence is by more than a factor two weaker in modified contour improved perturbation theory. The last term of the expansion is reduced, and renormalization scheme dependence remains approximately equal. The extracted QCD coupling at the tau mass scale is by 2$%$ lower than the "contour improved" value. We find $\alpha_s(M_Z^2)=0.1211\pm 0.0010$.