Determination of alpha(s) using OPAL hadronic event shapes at sqrt(s) = 91 - 209 GeV and resummed NNLO calculations

Abstract

Hadronic event shape distributions from e_s16e- annihilation measured by the OPAL experiment at centre-of-mass energies between 91 GeV and 209 GeV are used to determine the strong coupling {alpha}S. 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_s16NLLA). The combined NNLO result from all variables and centre-of-mass energies is {alpha}S(mZ0) = 0.1201 {pm} 0.0008(stat.) {pm} 0.0013(exp.) {pm} 0.0010(had.) {pm} 0.0024(theo.). while the combined NNLO_s16NLLA result is {alpha}S(mZ0) = 0.1189 {pm} 0.0008(stat.) {pm} 0.0016(exp.) {pm} 0.0010(had.) {pm} 0.0036(theo.). The completeness of the NNLO and NNLO_s16NLLA 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_s16NLLA predictions only. The observed energy dependence of {alpha}S agrees with the QCD prediction of asymptotic freedom and excludes the absence of running.