6,358 research outputs found

    \alpha_S from LEP

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    Recent results on measurements of the strong coupling αS\alpha_S from LEP are reported. These include analyses of the 4-jet rate using the Durham or Cambridge algorithm, of hadronic Z0Z^0 decays with hard final state photon radiation, of scaling violations of the fragmentation function, of the longitudinal cross section, of the Z0Z^0 lineshape and of hadronic τ\tau lepton decays.Comment: 3 pages, 2 figures, invited parallel talk at EPS HEP 2007 Manchester, added comment on estimation of theory error in section 5 and new ref [10

    Studies of Fragmentation Functions using e+e- Annihilation Data from PETRA and LEP

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    We present studies of the angular and momentum distributions of charged particles in hadronic final states of e+e- annihilation. Some results are derived from reanalysis of data of the JADE experiment operating at the PETRA e+e- collider at DESY from 1979 to 1986 while other data are from OPAL.Comment: 3 pages, 2 figures, contribution to Quark Confinement V, Gargnano, Italy, 10-14 Sep 200

    Studies of the 4-jet rate and of moments of event shape observables using JADE data

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    Data from e+e- annihilation into hadrons collected by the JADE experiment at centre-of-mass energies between 14 and 44 GeV were used to study the 4-jet rate using the Durham algorithm as well as the first five moments of event shape observables. The data were compared with NLO QCD predictions, augmented by resummed NLLA calculations for the 4-jet rate, in order to extract values of the strong coupling constant alpha_S. The preliminary results are alpha_S(MZ) = 0.1169 +/- 0.0026 (4-jet rate) and alpha_S(MZ) = 0.1286 +/- 0.0072 (moments) consistent with the world average value. For some of the higher moments systematic deficiencies of the QCD predictions are observed.Comment: Contribution to proceedings of ICHEP 2004, Beijing, China, 4 page

    Power Corrections in Electron-Positron Annihilation: Experimental Review

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    Experimental studies of power corrections with e+e- data are reviewed. An overview of the available data for jet and event shape observables is given and recent analyses based on the Dokshitzer-Marchesini-Webber (DMW) model of power corrections are summarised. The studies involve both distributions of the observables and their mean values. The agreement between perturbative QCD combined with DMW power corrections and the data is generally good, and the few exceptions are discussed. The use of low energy data sets highlights deficiencies in the existing calculations for some observables. A study of the finiteness of the physical strong coupling at low energies using hadronic Ď„\tau decays is shown.Comment: 10 pages, 6 figures, 2 tables, contribution to FRIF workshop on first principles non-perturbative QCD of hadron jets (Jan 2006

    Review of alpha_s Measurements

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    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.Comment: 4 pages, 1 figure, 1 table, contribution to ICHEP 2006 (Moscow) proceeding
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