Precision physics with QCD

Antonio Pich, Y. Foka, N. Brambilla, V. Kovalenko
2017 EPJ Web of Conferences  
The four-loop determination of the strong coupling from fully inclusive observables is reviewed. Special attention is given to the low-energy measurement extracted from the hadronic τ decay width. A recent exhaustive analysis of the ALEPH data, exploring several complementary methodologies with very different sensitivities to inverse power corrections and duality violations, confirms the strong suppression of non-perturbative contributions to R_τ. It gives the value α_s(m_τ^2)= 0.328 ± 0.013,
more » ... ich implies α_s(M_Z^2)= 0.1197 ± 0.0015. The excellent agreement with the direct measurement at the Z peak, α_s(M_Z^2)= 0.1196 ± 0.0030, provides a beautiful test of asymptotic freedom. Together with the most recent lattice average from FLAG and the NNLO determinations from e^+e^-, PDFs and collider data quoted by the PDG, these two inclusive determinations imply a world average value α_s(M_Z^2)= 0.1180 ± 0.0010.
doi:10.1051/epjconf/201713701016 fatcat:5gyoraci6zffjoeiemlfzc24fe