title: Order alphas4 QCD corrections to Z and tau decays.
abstract: Using recently developed methods for the evaluation of five-loop amplitudes in perturbative QCD, corrections of order alphas4 for the nonsinglet part of the cross section for electron-positron annihilation into hadrons and for the decay rates of the Z boson and the tau lepton into hadrons are evaluated. The new terms lead to a significant stabilization of the perturbative series, to a reduction of the theory uncertainly in the strong coupling constant alphas, as extracted from these measurements, and to a small shift of the central value, moving the two central values closer together. The agreement between two values of alphas measured at vastly different energies constitutes a striking test of asymptotic freedom. Combining the results from Z and tau decays we find alphas(MZ)=0.1198+/-0.0015 as one of the most precise and presently only result for the strong coupling constant in order alphas4.
authors.affiliation: Institute of Nuclear Physics, Moscow State University, Moscow 119899, Russia.
authors.forename: P A
authors.initials: PA
authors.lastname: Baikov
authors.forename: K G
authors.initials: KG
authors.lastname: Chetyrkin
authors.forename: J H
authors.initials: JH
authors.lastname: Kühn