Determination of αS using OPAL hadronic event shapes at \(\sqrt{s} = 91\mbox{--}209~\mathrm{GeV}\) and resummed NNLO calculations
2011
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
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while the combined NNLO + NLLA result is
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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.
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