A Simultaneous Measurement of the QCD Colour Factors and the Strong Coupling

TL;DR

This paper reports a precise measurement of QCD colour factors and the strong coupling constant using e+e- collision data, confirming the non-abelian gauge structure of QCD and aligning with theoretical expectations.

Contribution

It provides the first simultaneous measurement of the QCD colour factors and alpha(s) from angular correlations in 4-jet events at LEP.

Findings

CA measured as 3.02 ± 0.25 (stat.) ± 0.49 (syst.)

CF measured as 1.34 ± 0.13 (stat.) ± 0.22 (syst.)

alpha(s)(M_Z) measured as 0.120 ± 0.011 (stat.) ± 0.020 (syst.)

Abstract

Using data from e+e- annihilation into hadrons, taken with the OPAL detector at LEP at the Z pole between 1991 and 1995, we performed a simultaneous measurement of the colour factors of the underlying gauge group of the strong interaction, CF and CA, and the strong coupling, alpha(s). The measurement was carried out by fitting next-to-leading order perturbative predictions to measured angular correlations of 4-jet events together with multi-jet related variables. Our results, CA = 3.02 +/- 0.25 (stat.) +/- 0.49 (syst.), CF = 1.34 +/- 0.13 (stat.) +/- 0.22 (syst.), alpha(s)(M_Z) = 0.120 +/- 0.011 (stat.) +/- 0.020 (syst.), provide a test of perturbative QCD in which the only assumptions are non-abelian gauge symmetry and standard hadronization models. The measurements are in agreement with SU(3) expectations for CF and CA and the world average of alpha(s)(M_Z).