10,523 research outputs found

    Is there elliptic flow without transverse flow?

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    Azimuthal anisotropy of final particle distributions was originally introduced as a signature of transverse collective flow. We show that finite anisotropy in momentum space can result solely from the shape of the particle emitting source. However, by comparing the differential anisotropy to recent data from STAR collaboration we can exclude such a scenario, but instead show that the data favour strong flow as resulting from a hydrodynamical evolution.Comment: To appear in proceedings of Quark Matter 2001, 4 pages LaTeX, uses espcrc1.st

    Momentum anisotropies in the quark coalescence model

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    Based on the quark coalescence model, we derive relations among the momentum anisotropies of mesons and baryons in relativistic heavy ion collisions from a given, but arbitrary azimuthal distribution for the partons. Besides the familiar even Fourier coefficients such as the elliptic flow, we also pay attention to odd Fourier coefficients such as the directed flow, which has been observed at finite rapidity even at RHIC energies.Comment: 5 page

    Transverse momentum spectra and elliptic flow in ideal hydrodynamics and geometric scaling

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    In an ideal hydrodynamic model, with an equation of state where the confinement-deconfinement transition is a cross-over at Tco=196MeVT_{co}=196 MeV, we have simulated s\sqrt{s}=200 GeV Au+Au collisions. Simultaneous description of the experimental charged particle's pTp_T spectra and elliptic flow require that in central (0-10%) Au+Au collisions, initial energy density scales with the binary collision number density. In less central collisions, experimental data demand scaling with the participant density. Simulation studies also indicate that in central collisions viscous effects are minimal.Comment: 4 pages, 3 figures

    Direct photon production from viscous QGP

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    We simulate direct photon production in evolution of viscous QGP medium. Photons from Compton and annihilation processes are considered. Viscous effect on photon production is very strong and reliable simulation is possible only in a limited pTp_T range. For minimally viscous fluid η/s\eta/s=0.08), direct photons can be reliably computed only up to pTp_T \leq 1.3 GeV. With reduced viscosity (η/s\eta/s=0.04), the limit increases to pTp_T \leq 2GeV.Comment: 6 pages, 5 figure

    Di-jet hadron pair correlation in a hydrodynamical model with a quenching jet

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    In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium, leading to suppressed production of high-pTp_T hadrons. Assuming that the deposited energy quickly thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP fluid. Hydrodynamic evolution and subsequent particle emission depend on the jet trajectories. Azimuthal distribution of excess π\pi^- due to quenching jet, averaged over all the trajectories, reasonably well reproduce the di-hadron correlation as measured by the STAR and PHENIX collaboration in central and in peripheral Au+Au collisions.Comment: 5 pages, 4 figures. Some minor corrections are made in the revised manuscrip

    Hydrodynamic simulation of elliptic flow

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    We use a hydrodynamic model to study the space-time evolution transverse to the beam direction in ultrarelativistic heavy-ion collisions with nonzero impact parameters. We focus on the influence of early pressure on the development of radial and elliptic flow. We show that at high energies elliptic flow is generated only during the initial stages of the expansion while radial flow continues to grow until freeze-out. Quantitative comparisons with SPS data from semiperipheral Pb+Pb collisions suggest the applicability of hydrodynamical concepts already \approx 1 fm/c after impact.Comment: 4 pages, 5 figures, proceedings for Quark Matter 9

    Evolution of pion HBT radii from RHIC to LHC -- Predictions from ideal hydrodynamics

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    We present hydrodynamic predictions for the charged pion HBT radii for a range of initial conditions covering those presumably reached in Pb+Pb collisions at the LHC. We study central (b=0) and semi-central (b=7fm) collisions and show the expected increase of the HBT radii and their azimuthal oscillations. The predicted trends in the oscillation amplitudes reflect a change of the final source shape from out-of-plane to in-plane deformation as the initial entropy density is increased.Comment: 6 pages, incl. 5 figures. Contribution to the CERN Theory Institute Workshop "Heavy Ion Collisions at the LHC -- Last Call for Predictions", CERN, 14 May - 8 June 2007, to appear in J. Phys.

    Consequences of energy conservation in relativistic heavy-ion collisions

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    Complete characterization of particle production and emission in relativistic heavy-ion collisions is in general not feasible experimentally. This work demonstrates, however, that the availability of essentially complete pseudorapidity distributions for charged particles allows for a reliable estimate of the average transverse momenta and energy of emitted particles by requiring energy conservation in the process. The results of such an analysis for Au+Au collisions at sqrt{s_{NN}}= 130 and 200 GeV are compared with measurements of mean-p_T and mean-E_T in regions where such measurements are available. The mean-p_T dependence on pseudorapidity for Au+Au collisions at 130 and 200 GeV is given for different collision centralities.Comment: 8 pages, 8 figures, Submitted to Phys. Rev.

    Classical Strongly Coupled QGP: VII. Shear Viscosity and Self Diffusion

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    We construct the Liouville operator for the SU(2) classical colored Coulomb plasma (cQGP) for arbitrary values of the Coulomb coupling Γ=V/K\Gamma=V/K, the ratio of the mean Coulomb to kinetic energy. We show that its resolvent in the classical colored phase space obeys a hierarchy of equations. We use a free streaming approximation to close the hierarchy and derive an integral equation for the time-dependent structure factor. Its reduction by projection yields hydrodynamical equations in the long-wavelength limit. We discuss the character of the hydrodynamical modes at strong coupling. The shear viscosity is shown to exhibit a minimum at Γ8\Gamma\approx 8 near the liquid point. This minimum follows from the cross-over between the single particle collisional regime which drops as 1/Γ5/21/\Gamma^{5/2} and the hydrodynamical collisional regime which rises as Γ1/2\Gamma^{1/2}. The self-diffusion constant drops as 1/Γ3/21/\Gamma^{3/2} irrespective of the regime. We compare our results to molecular dynamics simulations of the SU(2) colored Coulomb plasma. We also discuss the relevance of our results for the quantum and strongly coupled quark gluon plasma (sQGP)Comment: 36 pages, 14 figure

    Conservation Laws and the Multiplicity Evolution of Spectra at the Relativistic Heavy Ion Collider

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    Transverse momentum distributions in ultra-relativistic heavy ion collisions carry considerable information about the dynamics of the hot system produced. Direct comparison with the same spectra from p+pp+p collisions has proven invaluable to identify novel features associated with the larger system, in particular, the "jet quenching" at high momentum and apparently much stronger collective flow dominating the spectral shape at low momentum. We point out possible hazards of ignoring conservation laws in the comparison of high- and low-multiplicity final states. We argue that the effects of energy and momentum conservation actually dominate many of the observed systematics, and that p+pp+p collisions may be much more similar to heavy ion collisions than generally thought.Comment: 15 pages, 14 figures, submitted to PRC; Figures 2,4,5,6,12 updated, Tables 1 and 3 added, typo in Tab.V fixed, appendix B partially rephrased, minor typo in Eq.B1 fixed, minor wording; references adde