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Order alphas4 QCD corrections to Z and tau decays
P A Baikov1, K G Chetyrkin, J H Kühn
1Institute of Nuclear Physics, Moscow State University, Moscow 119899, Russia.
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.
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