QCD studies in e+e- annihilation from 30GeV to 189GeV

TL;DR

This paper analyzes hadronic event structures from e+e- collisions across a wide energy range, testing QCD predictions, extracting the strong coupling constant, and confirming the running of alpha_s as expected in QCD.

Contribution

It provides new measurements of event shape variables and their energy dependence, and determines the strong coupling constant at multiple energies using resummed QCD calculations.

Findings

Confirmed the energy dependence of event shape variables

Measured alpha_s(m_Z) = 0.1215 with uncertainties

Supported the QCD prediction of alpha_s running

Abstract

We present results obtained from a study of the structure of hadronic events recorded by the L3 detector at various centre-of-mass energies. The distributions of event shape variables and the energy dependence of their mean values are measured from 30GeV to 189GeV and compared with various QCD models. The energy dependence of the moments of event shape variables is used to test a power law ansatz for the non-perturbative component. We obtain a universal value of the non-perturbative parameter alpha_0 = 0.537 +/- 0.073. From a comparison with resummed O(alpha_s^2) QCD calculations, we determine the strong coupling constant at each of the selected energies. The measurements demonstrate the running of alpha_s as expected in QCD with a value of alpha_s(m_Z) = 0.1215 +/- 0.0012 (exp) +/- 0.0061 (th).