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9th International Workshop on Tau Lepton Physics (Tau06), Pisa : Italie (2006)
ALEPH Tau Spectral Functions and QCD
M. Davier1, A. Hoecker2, Z. Zhang1

Hadronic $\tau$ decays provide a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables based on the spectral functions of hadronic $\tau$ decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong coupling constant, quark and gluon condensates. Using the ALEPH spectral functions and branching ratios, complemented by some other available measurements, and a revisited analysis of the theoretical framework, the value $\asm = 0.345 \pm 0.004_{\rm exp} \pm 0.009_{\rm th}$ is obtained. Taken together with the determination of \asZ from the global electroweak fit, this result leads to the most accurate test of asymptotic freedom: the value of the logarithmic slope of $\alpha_s^{-1}(s)$ is found to agree with QCD at a precision of 4%. The value of \asZ obtained from $\tau$ decays is $\asZ = 0.1215 \pm 0.0004_{\rm exp} \pm 0.0010_{\rm th} \pm 0.0005_{\rm evol}= 0.1215 \pm 0.0012$.
1 :  LAL - Laboratoire de l'Accélérateur Linéaire
2 :  CERN - European Organization for Nuclear Research
Physique/Physique des Hautes Energies - Phénoménologie
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