Determination of the Strong Coupling \boldmath{\as} from hadronic Event Shapes and NNLO QCD predictions using JADE Data

TL;DR

This paper uses JADE data from electron-positron collisions to determine the strong coupling constant  at various energies, employing advanced NNLO QCD calculations and resummation techniques, confirming QCD predictions of asymptotic freedom.

Contribution

It provides a precise determination of  using NNLO and NNLO+NLLA calculations, demonstrating improved stability and energy dependence consistent with QCD.

Findings

(M_Z)=0.1210 b1 0.0007 (stat.) b1 0.0021 (expt.) b1 0.0044 (had.) b1 0.0036 (theo.)

(M_Z)=0.1172 b1 0.0006 (stat.) b1 0.0020 (expt.) b1 0.0035 (had.) b1 0.0030 (theo.)

The energy dependence of  confirms QCD's asymptotic freedom and rules out no-running at 99% confidence.

Abstract

Event Shape Data from $e^+e^-$ 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+NLLA) 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 +/- 0.0007(stat.) +/- 0.0021(expt.) +/- 0.0044(had.) +/- 0.0036(theo.) and with the NNLO+NLLA calculations the combined value is $\alpha_S$= 0.1172 +/- 0.0006(stat.) +/- 0.0020(expt.) +/- 0.0035(had.) +/- 0.0030(theo.) . The stability of the NNLO and NNLO+NLLA results with respect to missing higher order contributions, studied by variations of the renormalisation scale, is improved compared to previous results obtained with NLO+NLLA 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.