The 2009 world average of α s

Siegfried Bethke

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

EPJ

The 2009 world average of α _s

Siegfried Bethke^*

MPI für Physik, Föhringer Ring 6, 80805, Munich, Germany

Received: 10 August 2009
Published online: 23 October 2009

Abstract

Measurements of α _s, 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 α _s. 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 α _s(Q ²), covering energy scales from Q≡M _τ=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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EPJ

The 2009 world average of α s

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The 2009 world average of α _s