A Measurement of the QCD Colour Factors using Event Shape Distributions at sqrt(s)=14 GeV to 189 GeV

TL;DR

This paper measures QCD color factors and active quark flavors using event shape distributions from e+e- collisions across a wide energy range, employing power correction models to reduce hadronisation biases.

Contribution

It provides the first comprehensive measurement of QCD color factors and quark flavors over a broad energy spectrum using event shape data with reduced hadronisation model dependence.

Findings

Results agree with SU(3) QCD predictions

Measured C_A and C_F are consistent with theoretical values

Number of active quark flavors aligns with expectations

Abstract

Measurements of the QCD colour factors C_A and C_F and of the number of active quark flavours n_f in the process e+e- -> hadrons at high energy are presented. They are based on fits of O(alpha_S**2)+NLLA QCD calculations to distributions of the event shape observables 1-T, C, B_T and B_W measured at centre-of-mass energies from 14 GeV to 189 GeV. Hadronisation effects are approximated with power correction calculations which also depend on the QCD gauge structure. In this approach potential biases from hadronisation models are reduced. Our results for individually measured quantities are n_f = 5.64 +- 1.35, C_A = 2.88 +- 0.27 and C_F = 1.45 +- 0.27 in good agreement with QCD based on the SU(3) symmetry group where n_f=5 for the energies considered here, C_A=3 and C_F=4/3. From simultaneous fits of C_A and C_F we find C_A = 2.84 +- 0.24 and C_F = 1.29 +- 0.18, which is also in good agreement with the QCD expectation.