# TTP08-21 Precise Determinations of the Strong Coupling Constant

TTP08-21 Precise Determinations of the Strong Coupling Constant

TTP08-21 Precise Determinations of the Strong Coupling Constant

Recent results for the cross section of electron-positron annihilation into hadrons and for the decay rates of the $Z$-boson and the $\tau$-lepton into hadrons including corrections of order $\alpha_s^4$ are reviewed. The consistency between two values of $\alpha_s$ measured at vastly different energies constitutes a striking test of asymptotic freedom. Combining the results from $Z$ and $\tau$ decays we find $\alpha_s(M_Z)=0.1198 \pm 0.0015$ as one of the most precise and presently only NNNLO result for the strong coupling constant.

 J.H. Kühn Nucl. Phys. B (Proc.Suppl.) 181 (2008) (141-145). Contribution to “PHIPSI08, International Workshop on e+e- collisions from Phi to Psi.” Frascati, Italy, 7-10 April 2008 PDF PostScript