4,379 research outputs found

    Jet Quenching

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    A short summary of the physics underlying jet quenching is givenComment: 10 pages, LaTex, 11 postscript figures, Proceedings of Quark Matter 2002, Nantes, France, July 18-24, 200

    Deciphering the properties of the medium produced in heavy ion collisions at RHIC by a pQCD analysis of quenched large p‚ä•p_{\perp} ŌÄ0\pi^0 spectra

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    We discuss the question of the relevance of perturbative QCD calculations for analyzing the properties of the dense medium produced in heavy ion collisions. Up to now leading order perturbative estimates have been worked out and confronted with data for quenched large p‚ä•p_{\perp} hadron spectra. Some of them are giving paradoxical results, contradicting the perturbative framework and leading to speculations such as the formation of a strongly interacting quark-gluon plasma. Trying to bypass some drawbacks of these leading order analysis and without performing detailed numerical investigations, we collect evidence in favour of a consistent description of quenching and of the characteristics of the produced medium within the pQCD framework.Comment: 10 pages, 3 figure

    Comparison of theory with experiment for positron production from high-energy electrons moving along crystal axes

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    Various positron distributions are obtained using an approach developed earlier for the description of electron-photon showers in axially aligned single crystals. Based on these distributions, characteristics of the positron yield measured in recent experiments are calculated. Theoretical estimations display a rather good agreement with experimental results obtained using 3 to 10 GeV electrons aligned to the - axis of the tungsten crystals.Comment: 10 pages, 6 Postscript figure

    On the Angular Dependence of the Radiative Gluon Spectrum

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    The induced momentum spectrum of soft gluons radiated from a high energy quark produced in and propagating through a QCD medium is reexamined in the BDMPS formalism. A mistake in our published work (Physical Review C60 (1999) 064902) is corrected. The correct dependence of the fractional induced loss R(őłcone)R(\theta_{{\rm cone}}) as a universal function of the variable őłcone2L3q^\theta^2_{{\rm cone}} L^3 \hat q where LL is the size of the medium and q^\hat q the transport coefficient is presented. We add the proof that the radiated gluon momentum spectrum derived in our formalism is equivalent with the one derived in the Zakharov-Wiedemann approach.Comment: LaTex, 5 pages, 1 figur

    On p_T-broadening of high energy partons associated with the LPM effect in a finite-volume QCD medium

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    We study the contributions from radiation to p‚ä•p_{\perp}-broadening of a high energy parton traversing a QCD medium with a finite length LL. The interaction between the parton and the medium is described by decorrelated static multiple scattering. Amplitudes of medium-induced gluon emission and parton self-energy diagrams are evaluated in the soft gluon limit in the BDMPS formalism. We find both the double-logarithmic correction from incoherent scattering, which is parametrically the same as that in single scattering, and the logarithmic correction from the LPM effect. Therefore, we expect a parametrically large correction from radiation to the medium-induced p‚ä•p_\perp-broadening in perturbative QCD.Comment: 19 pages, focusing only on calculations about the medium-induced diagrams, origin for double-log reinterpreted, final version to appear in JHE

    Partonic Energy Loss and the Drell-Yan Process

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    We examine the current status of the extraction of the rate of partonic energy loss in nuclei from A dependent data. The advantages and difficulties of using the Drell-Yan process to measure the energy loss of a parton traversing a cold nuclear medium are discussed. The prospects of using relatively low energy proton beams for a definitive measurement of partonic energy loss are presented.Comment: 12 pages, 2 figure

    Mixed and discontinuous finite volume element schemes for the optimal control of immiscible flow in porous media

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    We introduce a family of hybrid discretisations for the numerical approximation of optimal control problems governed by the equations of immiscible displacement in porous media. The proposed schemes are based on mixed and discontinuous finite volume element methods in combination with the optimise-then-discretise approach for the approximation of the optimal control problem, leading to nonsymmetric algebraic systems, and employing minimum regularity requirements. Estimates for the error (between a local reference solution of the infinite dimensional optimal control problem and its hybrid approximation) measured in suitable norms are derived, showing optimal orders of convergence
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