958 research outputs found

    Gluon Distributions and Color Charge Correlations in a Saturated Light-cone Wavefunction

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    We describe the light-cone wavefunction in the saturation regime in terms of the density of gluons per unit of transverse phase space, the occupation number, and in terms of the color charge correlator. The simple McLerran- Venugopalan model gives what are claimed to be general results for the phase space gluon density, but it does not well describe the general case for the charge correlator. We derive the general momentum dependence and rapidity dependence of the color charge correlator which exhibits strong color shielding. A simplel physical picture which leads to these general results is described.Comment: 17 pages, Latex, 7 figure

    Isotropization and Thermalization in Heavy Ion Collisions

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    We argue that isotropization and, consequently, thermalization of the system of gluons and quarks produced in an ultrarelativistic heavy ion collision does not follow from Feynman diagram analysis to any order in the coupling constant. We conclude that the apparent thermalization of quarks and gluons, leading to success of perfect fluid hydrodynamics in describing heavy ion collisions at RHIC, can only be attributed to the non-perturbative QCD effects not captured by Feynman diagrams. We proceed by modeling these non-pertrubative thermalization effects using viscous hydrodynamics. We point out that matching Color Glass Condensate inital conditions with viscous hydrodynamics leads to continuous evolution of all components of energy-momentum tensor and, unlike the case of ideal hydrodynamics, does not give a discontinuity in the longitudinal pressure. An important consequence of such a matching is a relationship between the thermalization time and shear viscosity: we observe that small viscosity leads to short thermalization time.Comment: Includes new results. 8 pages, 1 figure, based on proceedings contributions at "Quark Matter 2005" conference in Budapest, Hungary, August 4-9, 2005 and at the workshop on "Quark-Gluon Plasma Thermalization" in Vienna, Austria, August 10-12, 200

    Correlation Functions and Cumulants in Elliptic Flow Analysis

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    We consider various methods of flow analysis in heavy ion collisions and compare experimental data on corresponding observables to the predictions of our saturation model proposed earlier. We demonstrate that, due to the nature of the standard flow analysis, azimuthal distribution of particles with respect to reaction plane determined from the second order harmonics should always be proportional to cos⁥2(ϕ−ΚR)\cos 2(\phi-\Psi_R) independent of the physical origin of particle correlations (flow or non-flow). The amplitude of this distribution is always physical and proportional to v2v_2. Two-particle correlations analysis is therefore a more reliable way of extracting the shape of physical azimuthal anisotropy. We demonstrate that two-particle correlation functions generated in our minijet model of particle production are in good agreement with the data reported by PHENIX. We discuss the role of non-flow correlations in the cumulant flow analysis and demonstrate using a simple example that if the flow is weak, higher order cumulants analysis does not significantly reduce the contribution of non-flow correlations to elliptic flow observable v2v_2 in RHIC data.Comment: 18 pages, 1 figure; v2: IR safety and v2(pT) from 4th order cumulant discussions adde

    Theory Summary: International Symposium on Multiparticle Dynamics 2008

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    I summarize the theory talks presented at the International Symposium on Multiparticle Dynamics 2008.Comment: 20 pages, 16 figures; v2: reference added; v3: typos correcte

    Toward Equilibration in the Early Stages After a High Energy Heavy Ion Collision

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    The early stages in the evolution of the gluons produced in the central region of a head-on high-energy heavy ion collision is studied. An equation is given for the rate of change of transverse momentum into longitudinal momentum where the longitudinal direction is along the collision axis. We are able to follow the system up to the time where equilibration seems to be setting in, but we are unable to actually follow the system as it reaches equilibrium.Comment: 18 pages, Late