Measurement of event shape distributions and moments in e+e- -> hadrons at 91-209 GeV and a determination of alpha_s

TL;DR

This paper analyzes event shape distributions in electron-positron collisions across a wide energy range to measure the strong coupling constant alpha_s and test its energy dependence as predicted by QCD.

Contribution

It provides a precise measurement of alpha_s(M_Z) from event shape data and confirms its running with energy consistent with QCD predictions.

Findings

Measured alpha_s(M_Z) = 0.1191 ± 0.0014 (total)

Confirmed the energy dependence of alpha_s consistent with QCD

Provided detailed distributions and moments of event shape observables

Abstract

We have studied hadronic events from e+e- annihilation data at centre-of-mass energies from 91 to 209 GeV. We present distributions of event shape observables and their moments at each energy and compare with QCD Monte Carlo models. From the event shape distributions we extract the strong coupling alpha_s and test its evolution with energy scale. The results are consistent with the running of alpha_s expected from QCD. Combining all data, the value of alpha_s(M_Z) is determined to be alpha_s(M_Z) = 0.1191 +- 0.0005 (stat.) +- 0.0010 (expt.) +- 0.0011 (hadr.) +- 0.0044 (theo.). The energy evolution of the moments is also used to determine a value of alpha_s with slightly larger errors: alpha_s(M_Z) = 0.1223 +- 0.0005 (stat.) +- 0.0014 (expt.) +- 0.0016 (hadr.) +0.0054 -0.0036 (theo.).