Determination of αS using OPAL hadronic event shapes at √ s = 91-209 GeV and resummed NNLO calculations

Abstract

Hadronic event shape distributions from e+e- annihilation measured by the OPAL experiment at centre-of-mass energies between 91 GeV and 209 GeV are used to determine the strong coupling αS. The results are based on QCD predictions complete to the next-to-next-to-leading order (NNLO), and on NNLO calculations matched to the resummed next-to-leading-log-approximation terms (NNLO + NLLA). The combined NNLO result from all variables and centre-of-mass energies is [Equation not available: see fulltext.] while the combined NNLO + NLLA result is [Equation not available: see fulltext.] The completeness of the NNLO and NNLO + NLLA results with respect to missing higher order contributions, studied by varying the renormalization scale, is improved compared to previous results based on NLO or NLO + NLLA predictions only. The observed energy dependence of αS agrees with the QCD prediction of asymptotic freedom and excludes the absence of running. © 2011 The Author(s).