Determination of the Strong Coupling $lpha_S$ from hadronic Event Shapes and NNLO QCD predictions using JADE Data

Abstract

Event Shape Data from $e^_s16e^-$ annihilation into hadrons collected by the JADE experiment at centre-of-mass energies between 14 GeV and 44 GeV are used to determine the strong coupling $alpha_S$. QCD predictions complete to next-to-next-to-leading order (NNLO), alternatively combined with resummed next-to-leading-log-approximation (NNLO_s16NLLA) calculations, are used. The combined value from six different event shape observables at the six JADE centre-of-mass energies using the NNLO calculations is $alpha_S(M_Z)$= 0.1210 _s16/- 0.0007(stat.) _s16/- 0.0021(expt.) _s16/- 0.0044(had.) _s16/- 0.0036(theo.) and with the NNLO_s16NLLA calculations the combined value is $alpha_S$= 0.1172 _s16/- 0.0006(stat.) _s16/- 0.0020(expt.) _s16/- 0.0035(had.) _s16/- 0.0030(theo.) . The stability of the NNLO and NNLO_s16NLLA results with respect to missing higher order contributions, studied by variations of the renormalisation scale, is improved compared to previous results obtained with NLO_s16NLLA or with NLO predictions only. The observed energy dependence of $alpha_S$ agrees with the QCD prediction of asymptotic freedom and excludes absence of running with 99% confidence level.