Determination of the QCD Coupling $\alpha_s$
TL;DR: In this paper, the authors reviewed the theoretical basics and experimental determinations of the coupling parameter of the Strong Interaction, and determined the world average value of $\alpha_s, expressed at the energy scale of the rest mass of the $Z^0$ boson, from analyses which are based on complete NNLO perturbative QCD.
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Abstract: Theoretical basics and experimental determinations of the coupling parameter of the Strong Interaction, $\alpha_s$, are reviewed. The world average value of $\alpha_s$, expressed at the energy scale of the rest mass of the $Z^0$ boson, is determined from analyses which are based on complete NNLO perturbative QCD. The result is $\alpha_s (M_Z) = 0.1184 \pm 0.0031$. No significant deviations or systematic biases of subsamples of experimental results are found. From the observed energy dependence of $\alpha_s$, which is in excellent agreement with the expectations of QCD, the number of colour degrees of freedom can be constrained to $N_c = 3.03 \pm 0.12$.
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