2008/01/31 by P. A. Baikov, K. G. Chetyrkin, J. H. Kühn · 1 citation
Physics and Astronomy · #hep-ph
paper · pdf · doi:10.1103/physrevlett.101.012002
published as Phys.Rev.Lett.101:012002,2008 · few citations added, final published version
arxiv created 2008/07/04 · arxiv updated 2009/12/01
Using recently developed methods for the evaluation of five-loop amplitudes in perturbative QCD, corrections of order alphas4 for the cross section of 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 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.