====== TTP08-21 Precise Determinations of the Strong Coupling Constant ======
 
 
<hidden 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.
 </hidden>
|**J.H. K&uuml;hn**  | 
|**       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 **  |
| {{preprints:2008:ttp08-21.pdf|PDF}} {{preprints:2008:ttp08-21.ps|PostScript}}   |
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