A measurement of the QCD colour factors using event shape distributions at \(\sqrt{s}=14\) to 189 GeV

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2001-06, Vol.21 (2), p.199-210
• Main Authors: Kluth, S, PA Movilla Fernández, Bethke, S, Pahl, C, Pfeifenschneider, P
• Format: Article
• Language: English
• Subjects: Accuracy; Color; Flavor (particle physics); Hadrons; Quantum chromodynamics
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1007/s100520100742

Measurements of the QCD colour factors \(C_A\) and \(C_F\) and of the number of active quark flavours \(n_f\) in the process \(\mathrm{e^+e^-}\rightarrow\mathrm{hadrons}\) at high energy are presented. They are based on fits of \(\mathcal{O}(\alpha_s^2)\)+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 obtained from \(1-T\) and C arein 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 \(C_F\) with \(1-T\) and C we findwhich is also in good agreement with the QCD expectation.