Determination of the QCD Coupling $α_s$

Paper

Abstract

Theoretical basics and experimental determinations of the coupling parameter of the Strong Interaction,

, are reviewed. The world average value of

, expressed at the energy scale of the rest mass of the

boson, is determined from analyses which are based on complete NNLO perturbative QCD. The result is

. No significant deviations or systematic biases of subsamples of experimental results are found. From the observed energy dependence of

, which is in excellent agreement with the expectations of QCD, the number of colour degrees of freedom can be constrained to