137 research outputs found

    Eleven Years of QCD at LEP

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    Studies of hadronic final states of e+ee^+e^- annihilations, observed at the Large Electron Positron Collider LEP at CERN, are reviewed. The topics included cover measurements of αs\alpha_s, hadronic event shapes and hadronisation studies, tests of asymptotic freedom and of the non-Abelian gauge structure of QCD, differences between quark and gluon jets, tests of power corrections and selected results of two-photon scattering processes. The improvements obtained at LEP are demonstrated by comparing to results from the pre-LEP era. This article consists of a reproduction of slides presented at the LEPFest in October 2000, supplemented by a short descriptive text and a list of relevant references.Comment: 10 pages of text plus reproduction of 27 transparencies presented at the LEPFest at CERN, October 2000. To be published in Eur. Phys. Jour (direct) C; a higher resolution version of the viewgraphs can be obtained from: http://www.mppmu.mpg.de/~bethke/LEPQCDtalk-higres.pd

    Experimental Tests of Asymptotic Freedom

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    Quantum Chromodynamics (QCD), the gauge field theory of the Strong Interaction, has specific features, asymptotic freedom and confinement, which determine the behaviour of quarks and gluons in particle reactions at high and at low energy scales. QCD predicts that the strong coupling strength \as decreases with increasing energy or momentum transfer, and vanishes at asymptotically high energies. In this review, the history and the status of experimental tests of asymptotic freedom are summarised. The world summary of measurements of \as is updated, leading to an unambiguous verification of the running of \as and of asymptotic freedom, in excellent agreement with the predictions of QCD. Averaging a set of measurements balanced between different particle processes and the available energy range, results in a new and improved world average of \amz = 0.1189 \pm 0.0010 .Comment: 38 pages, 18 figure

    αs\alpha_s at Zinnowitz 2004

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    A review of measurements of αs\alpha_s is given, representing the status of April 2004. The results prove the energy dependence of αs\alpha_s and are in excellent agreement with the expectations of Quantum Chromodynamics, QCD. Evolving all results to the rest energy of the Z0Z^0 boson, the world average of αs(MZ)\alpha_s(M_Z) is determined from measurements which are based on QCD calculations in complete NNLO perturbation theory, giving αs(MZ)=0.1182±0.0027.\alpha_s(M_Z) = 0.1182 \pm 0.0027 .Comment: 8 pages, 4 figures, talk presented at the workshop Loops and Legs in Quantum Field Theory, April 2004, Zinnowitz (Germany

    QCD Tests at e+ee^+e^- Colliders

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    A short review of the history and a 'slide-show' of QCD tests in e+ee^+e^- annihilation is given. The world summary of measurements of αs\alpha_s is updated.Comment: Revised version: some references added and corrected; world summary of αs\alpha_s extended by result from polarized structure functions. 9 pages, 15 EPS figures; contribution to the CQD Euroconference 97 (Montpellier 1997

    Data Preservation in High Energy Physics - why, how and when?

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    Long-term preservation of data and software of large experiments and detectors in high energy physics is of utmost importance to secure the heritage of (mostly unique) data and to allow advanced physics (re-)analyses at later times. Summarising the work of an international study group, motivation, use cases and technical details are given for an organised effort to secure and enable future use of past, present and future experimental data. As a practical use case and motivation, the revival of JADE data and the corresponding latest results on measuring αs\alpha_s in NNLO QCD are reviewed.Comment: 5 pages, 3 figures; presentation given at the QCD10, Montpellier, France, June 201

    Wer fischt was? – Gemischte Bodenfischereien und ihre Auswirkungen auf die wichtigsten Nutzfischbestände in der Nordsee

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    Cod, haddock, whiting, saithe, plaice, sole and Norway lobster are 7 main target species of the demersal mixed fisheries in the North Sea, Skagerrak and Eastern Channel. Gadoids and Norway lobsters are mainly taken in the nor-thern North Sea by towed gears except beam trawls while the flatfish fisheries are conducted in the southern North Sea mainly using beam trawls. Recently, the central North Sea appears less fished by demersal gears. Towed nets including seines and beam trawls equipped with meshes of more than 100 mm resp. more than 80 mm were identified as the main gears effecting the depleted cod and reduced plaice stocks. The saithe sector, using towed nets with meshes of more than110 mm, longlines, gill nets and others, appears to affect the 7 species to a lesser extend. These results support the interim effort limitations by gear types, vessel and month as enforced by the European Commission since 2003. TAC regulations alone are considered inefficient to sustainably harvest stocks by mixed fisheries. A fleet-effort management method is developed estimating the fleets’ effects based on the sum of partial exploitation rates of the species in mixed fisheries weighted by the ratio of the precautionary reference Bpa and the actual SSB size as ecological quality objective. Applying such fleet effort management could result in increased catch possibilities of some stocks by fleets selecting mainly few and non-overexploited stocks while respecting precautionary management constraints in minimum SSB or maximum exploitation rates at the same time

    Experimental Tests of Asymptotic Freedom

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    Measurements which probe the energy dependence of αs\alpha_s, the coupling strength of the strong interaction, are reviewed. Jet counting in e+ee^+ e^- annihilation, combining results obtained in the centre of mass energy range from 22 to 133 GeV, provides direct evidence for an asymptotically free coupling, without the need to determine explicit values of αs\alpha_s. Recent results from jet production in epe p and in ppp \overline{p} collisions, obtained in single experiments spanning large ranges of momentum transfer, Q2Q^2, are in good agreement with the running of αs\alpha_s as predicted by QCD. Mass spectra of hadronic decays of τ\tau-leptons are analysed to probe the running αs\alpha_s in the very low energy domain, 0.7GeV2<Q2<Mτ20.7 GeV^2 < Q^2 < M_\tau^2. An update of the world summary of measurements of αs(Q2)\alpha_s(Q^2) consistently proves the energy dependence of αs\alpha_s and results in a combined average of αs(MZ)=0.118±0.006\alpha_s(M_Z) = 0.118 \pm 0.006.Comment: 11 pages, 8 Figures, LaTeX. To appear in Proc. of QCD Euroconference 96 at Montpellier, France, July 199

    The 2009 World Average of αs\alpha_s

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    Measurements of αs\alpha_s, the coupling strength of the Strong Interaction between quarks and gluons, are summarised and an updated value of the world average of αs(MZ)\alpha_s (M_Z) is derived. Building up on previous reviews, special emphasis is laid on the most recent determinations of αs\alpha_s. These are obtained from τ\tau-decays, from global fits of electroweak precision data and from measurements of the proton structure function \F_2, which are based on perturbative QCD calculations up to O(αs4)O(\alpha_s^4); from hadronic event shapes and jet production in \epem annihilation, based on O(αs3)O(\alpha_s^3) QCD; from jet production in deep inelastic scattering and from Υ\Upsilon decays, based on O(αs2)O(\alpha_s^2) QCD; and from heavy quarkonia based on unquenched QCD lattice calculations. Applying pragmatic methods to deal with possibly underestimated errors and/or unknown correlations, the world average value of αs(MZ)\alpha_s (M_Z) results in αs(MZ)=0.1184±0.0007\alpha_s (M_Z) = 0.1184 \pm 0.0007. The measured values of αs(Q)\alpha_s (Q), covering energy scales from Q \equiv \mtau = 1.78 GeV to 209 GeV, exactly follow the energy dependence predicted by QCD and therefore significantly test the concept af Asymptotic Freedom.Comment: 14 pages, 7 figure

    Status Report of the DPHEP Study Group: Towards a Global Effort for Sustainable Data Preservation in High Energy Physics

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    Data from high-energy physics (HEP) experiments are collected with significant financial and human effort and are mostly unique. An inter-experimental study group on HEP data preservation and long-term analysis was convened as a panel of the International Committee for Future Accelerators (ICFA). The group was formed by large collider-based experiments and investigated the technical and organisational aspects of HEP data preservation. An intermediate report was released in November 2009 addressing the general issues of data preservation in HEP. This paper includes and extends the intermediate report. It provides an analysis of the research case for data preservation and a detailed description of the various projects at experiment, laboratory and international levels. In addition, the paper provides a concrete proposal for an international organisation in charge of the data management and policies in high-energy physics
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