Determination of $α_s(M_τ^2)$ from Improved Fixed Order Perturbation Theory

Details Determination of $α_s(M_τ^2)$ from Improved Fixed Order Perturbation Theory Determination of $α_s(M_τ^2)$ from Improved Fixed Order Perturbation Theory

2012-02-13

arxiv.org/abs/1202.2672v1

Physics

High Energy Physics

High Energy Physics - Phenomenology

12 pages, 6 figures, uses revtex

Scientific paper

We revisit the extraction of $\alpha_s(M_\tau^2)$ from the QCD perturbative corrections to the hadronic $\tau$ branching ratio, using an improved fixed-order perturbation theory based on the explicit summation of all renormalization-group accessible logarithms, proposed some time ago in the literature. In this approach, the powers of the coupling in the expansion of the QCD Adler function are multiplied by a set of functions $D_n$, which depend themselves on the coupling and can be written in a closed form by iteratively solving a sequence of differential equations. We find that the new expansion has an improved behaviour in the complex energy plane compared to that of the standard fixed-order perturbation theory (FOPT), and is similar but not identical to the contour-improved perturbation theory (CIPT). With five terms in the perturbative expansion we obtain in the ${\bar{\rm MS}}$ scheme $ \alpha_s(M_\tau^2)= 0.338 \pm 0.010$.

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