Strong coupling from the tau hadronic width

Abstract

We determine the strong coupling constant alpha_s from the au; hadronic width using renormalization group summed expansion of the QCD Adlerfunction. The main theoretical uncertainty in the extraction of alpha_s is due tothe way in which renormalization group invariance is implemented and the yetuncalculated higher order terms in the QCD perturbative series. We show that new expansion exhibitsnice renormalization group improvement and the behaviour of the series is similar tostandard CIPT expansion. We further study the convergence properties of this expansion improved byBorel transformation and the analytical continuation in the Borel plane. We find that thenew, non-power expansions for different conformal mappings have remarkable convergence. Finally weprovide the value of strong coupling alpha_s using the new, non-power perturbative expansionswhich is alpha_s(M_ au ) = 0.3189+0.0145−0.0115, which translates to alpha_s(M_Z ) =0.1184+0.0018−0.0015.