Review of alpha_s determinations

Understand

The present knowledge on the strong coupling is briefly summarized.

• The most precise determinations of alpha_s, at different energies, are reviewed and compared at the Z mass scale, using the predicted QCD running.
• The impressive agreement achieved between experimental measurements and theoretical predictions constitutes a beautiful and very significant test of Asymptotic Freedom, establishing QCD as the fundamental theory of the strong interaction.
• The world average value of the strong coupling is found to be alpha_s(M_Z^2)= 0.1186 \pm 0.0007.