Institute for Theoretical Particle Physics (TTP)


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preprints:2008:ttp08-28 [2016/03/15 20:38] (current)
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 +====== TTP08-28 The Strong Coupling Constant at Low and High Energies ====== 
 +<hidden TTP08-28  The Strong Coupling Constant at Low and High Energies > 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 and requires the proper matching 
 + conditions 
 + at charm and bottom thresholds. 
 + Combining the results from $Z$ and $\tau$ decays 
 + leads to $\alpha_s(M_Z)=0.1198 \pm  0.0015$ as one of the most precise and 
 + presently only 
 + NNNLO result for the strong coupling constant. We report a recent 
 + determination of $\alpha_s$ 
 + which is based on a lattice evaluation of the pseudoscalar correlator for 
 + the charm quarks combined 
 + with continuum perturbation theory. 
 + </hidden> 
 +|**J.H. K&uuml;hn**  |  
 +|**      Contribution to "Continuous Advances in QCD, 2008" Minnepolis, USA, May 15 - 18, 2008; to be published in the proceedings **  | 
 +| {{preprints:2008:ttp08-28.pdf|PDF}} {{|PostScript}}   | 
 +| |