The European Physical Journal C

, Volume 64, Issue 4, pp 689–703

The 2009 world average of αs

Open AccessReview

DOI: 10.1140/epjc/s10052-009-1173-1

Cite this article as:
Bethke, S. Eur. Phys. J. C (2009) 64: 689. doi:10.1140/epjc/s10052-009-1173-1


Measurements of αs, the coupling strength of the Strong Interaction between quarks and gluons, are summarised and an updated value of the world average of \(\alpha_{\mathrm{s}}(M_{\mathrm{Z}^{0}})\) is derived. Special emphasis is laid on the most recent determinations of αs. These are obtained from τ-decays, from global fits of electroweak precision data and from measurements of the proton structure function F2, which are based on perturbative QCD calculations up to \(\mathcal{O}(\alpha_{\mathrm{s}}^{4})\); from hadronic event shapes and jet production in e+e annihilation, based on \(\mathcal{O}(\alpha_{\mathrm{s}}^{3})\) QCD; from jet production in deep inelastic scattering and from ϒ decays, based on \(\mathcal{O}(\alpha_{\mathrm{s}}^{2})\) QCD; and from heavy quarkonia based on unquenched QCD lattice calculations. A pragmatic method is chosen to obtain the world average and an estimate of its overall uncertainty, resulting in
$$\alpha_\mathrm{s}(M_{\mathrm{Z}^0})=0.1184\pm 0.0007.$$
The measured values of αs(Q2), covering energy scales from QMτ=1.78 GeV to 209 GeV, exactly follow the energy dependence predicted by QCD and therefore significantly test the concept of Asymptotic Freedom.


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© Springer-Verlag / Società Italiana di Fisica 2009

Authors and Affiliations

  1. 1.MPI für PhysikMunichGermany