The European Physical Journal C

, Volume 64, Issue 4, pp 689–703 | Cite as

The 2009 world average of αs

Open Access
Review

Abstract

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.

PACS

12.38.Qk 

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Copyright information

© Springer-Verlag / Società Italiana di Fisica 2009

Authors and Affiliations

  1. 1.MPI für PhysikMunichGermany

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