6,024 research outputs found

    The Determination of the Strong Coupling Constant

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    The strong coupling constant is one of the fundamental parameters of the standard model of particle physics. In this review I will briefly summarise the theoretical framework, within which the strong coupling constant is defined and how it is connected to measurable observables. Then I will give an historical overview of its experimental determinations and discuss the current status and world average value. Among the many different techniques used to determine this coupling constant in the context of quantum chromodynamics, I will focus in particular on a number of measurements carried out at the Large Electron Positron Collider (LEP) and the Large Hadron Collider (LHC) at CERN.Comment: A contribution to: The Standard Theory up to the Higgs discovery - 60 years of CERN, L. Maiani and G. Rolandi, ed

    Measurements of the bottom quark mass

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    I will review new measurements of the b quark mass, presented at this conference by ALEPH and DELPHI. A large set of observables has been used and detailed studies on jet algorithms have been performed. These measurements at the Z peak are consistent with the results obtained at the Upsilon scale when assuming the running of the b quark mass as predicted by perturbative QCD.Comment: 2 pages, 1 figure, presented at XXXth ICHEP, Osak

    Experimental status of measurements of alpha_s at LEP

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    A summary is given of the current status of measurements of the strong coupling constant αs\alpha_s performed at LEP. These include measurements from inclusive observables as well as from event shape variables. Recent results based on power law corrections are discussed.Comment: 3 pages, 2 figure

    Event shapes and power corrections in e+e- annihilitions

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    Hadronic final states in e+e- annihilitions at centre-of-mass energies from 14GeV up to 189GeV are studied in order to test recent predictions for power corrections to the mean values as well as the distributions of event shape variables.Comment: 3 pages, 3 figures, DIS99 Workshop, Berlin, Germany, April 19-23, 199

    Quark and Gluon Tagging at the LHC

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    Being able to distinguish light-quark jets from gluon jets on an event-by-event basis could significantly enhance the reach for many new physics searches at the Large Hadron Collider. Through an exhaustive search of existing and novel jet substructure observables, we find that a multivariate approach can filter out over 95% of the gluon jets while keeping more than half of the light-quark jets. Moreover, a combination of two simple variables, the charge track multiplicity and the pTp_T-weighted linear radial moment (girth), can achieve similar results. While this pair appears very promising, our study is only Monte Carlo based, and other discriminants may work better with real data in a realistic experimental environment. To that end, we explore many other observables constructed using different jet sizes and parameters, and highlight those that deserve further theoretical and experimental scrutiny. Additional information, including distributions of around 10,000 variables, can be found on this website http://jets.physics.harvard.edu/qvg .Comment: 5 pages, 3 figures. v2 published versio

    Measurements of the QCD Colour Factors at LEP

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    A summary of the measurements of the QCD colour factors at LEP is presented. Such measurements provide a test of the gauge group structure underlying the theory of strong interactions. A variety of methods have been applied by the various experiments, and perfect consistency with the expectation of QCD with SU(3) as gauge group is found.Comment: 9 pages, Latex, Talk presented at the 5th Topical Seminar on The Irresistible Rise of the Standard Model, San Miniato, Italy, April 199

    Measurements of αs\alpha_s from event shapes and the four-jet rate

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    New results from measurements of the strong coupling constant αs(MZ)\alpha_s(M_Z) at LEP are presented. In particular, a new LEP combination of results based on event-shape variables has become available, where a new method for the estimation of the theoretical uncertainty has been implemented. Furthermore, two other analyses are quoted, based on power corrections and the four-jet rate.Comment: Talk presented at the 31st International Conference on High Energy Physics, Amsterdam, 24-31 July 200

    Performance studies of scintillating ceramic samples exposed to ionizing radiation

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    Scintillating ceramics are a promising, new development for various applications in science and industry. Their application in calorimetry for particle physics experiments is expected to involve an exposure to high levels of ionizing radiation. In this paper, changes in performance have been measured for scintillating ceramic samples of different composition after exposure to penetrating ionizing radiation up to a dose of 38 kGy.Comment: 6 pages, 8 figures, to be published in the 2012 IEEE Nuclear Science Symposium Conference Recor
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