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Stefan Kluth
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Recent results on measurements of the strong coupling $alpha_S$ from LEP are reported. These include analyses of the 4-jet rate using the Durham or Cambridge algorithm, of hadronic $Z^0$ decays with hard final state photon radiation, of scaling violations of the fragmentation function, of the longitudinal cross section, of the $Z^0$ lineshape and of hadronic $tau$ lepton decays.
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Recent results on jet physics and tests of QCD from hadronic final states in $e^+e^-$ annihilation at PETRA and at LEP are reviewed, with special emphasis on hadronic event shapes, charged particle production rates, properties of quark and gluon jets and determinations of $alpha_s$. The data in the entire energy range from PETRA to LEP-2 are in broad agreement with the QCD predictions. The world summary of measurements of $alpha_s$ is updated and a detailed discussion of various methods to determine the overall error of $alpha_s (M_Z)$ is presented. The new world average is $alpha_s (M_Z) = 0.119 pm 0.004$. The size of the error depends on the treatment of correlated uncertainties.
Event shape data from e+e- annihilation into hadrons collected by the JADE experiment between sqrt(s)=14 and 44 GeV are used to determine the strong coupling alpha_S. QCD predictionscomplete to next-to-next-to-leading order (NLLO), alternatively combined with next-to-leading-log-approximation (NLLA) are used. The stability of the NNLO and NNLO+NLLA results with respect to variations of the renormalisation scale is improved compared to previous results obtained with next-to-leading-order (NLO) or NLO+NLLA predictions. The energy dependence of alpha_S agrees with the QCD prediction of asymptotic freedom and excludes absence of running with 99% confidence level.
The four LEP experiments ALEPH, DELPHI, L3 and OPAL successfully recorded e+e- collision data during the years 1989 to 2000. As part of the ordinary evolution in High Energy Physics, these experiments can not be repeated and their data is therefore unique. This article briefly reviews the data preservation efforts undertaken by the four experiments beyond the end of data taking. The current status of the preserved data and associated tools is summarised.
The evolution of the determination of the strong coupling constant $alpha_s$ from the leptonic branching ratios, the lifetime, and the invariant mass distributions of the hadronic final state of the $tau$ lepton over the last two decades is briefly reviewed. The improvements in the latest ALEPH update are described in some detail. Currently this is one of the most precise $alpha_s$ determinations. Together with the other determination at the $Z$ boson mass pole, they constitutes the most accurate test of the asymptotic freedom in QCD.
We present a review of measurements of alpha_S. The individual measurements are discussed and intermediate averages for classes of related measurements are found. The final average is built using the intermediate values. Correlations are treated consistently. The ICHEP 2006 world average is alpha_S(M_Z) = 0.1175 +/- 0.0011 dominated by the recent result from lattice QCD.
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