Determination of alphaS from Hadronic Event Shapes in e+e- Annihilation at 192 < sqrt(s) < 208 GeV

TL;DR

This paper measures the strong coupling constant alphaS at high energies using event shape variables from e+e- collisions, confirming its energy dependence as predicted by QCD.

Contribution

It provides new alphaS measurements at energies above 192 GeV and confirms the running of alphaS consistent with QCD predictions.

Findings

Measured alphaS at three energies: 194.4, 200.2, 206.2 GeV.

Combined results yield alphaS(mZ) = 0.1227 +- 0.0012 (experimental) +- 0.0058 (theoretical).

Confirmed the energy dependence of alphaS as expected in QCD.

Abstract

Results are presented from a study of the structure of high energy hadronic events recorded by the L3 detector at sqrt(s)>192 GeV. The distributions of several event shape variables are compared to resummed O(alphaS^2) QCD calculations. We determine the strong coupling constant at three average centre-of-mass energies: 194.4, 200.2 and 206.2 GeV. These measurements, combined with previous L3 measurements at lower energies, demonstrate the running of alphaS as expected in QCD and yield alphaS(mZ) = 0.1227 +- 0.0012 +- 0.0058, where the first uncertainty is experimental and the second is theoretical.