Publications (68)29.6 Total impact
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Article: Hydrodynamic Modeling of Heavy-Ion Collisions
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ABSTRACT: We review progress in the hydrodynamic description of heavy-ion collisions, focusing on recent developments in modeling the fluctuating initial state and event-by-event viscous hydrodynamic simulations. We discuss how hydrodynamics can be used to extract information on fundamental properties of quantum-chromo-dynamics from experimental data, and review successes and challenges of the hydrodynamic framework.01/2013; -
Article: Event-by-Event Anisotropic Flow in Heavy-ion Collisions from Combined Yang-Mills and Viscous Fluid Dynamics.
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ABSTRACT: Anisotropic flow coefficients v_{1}-v_{5} in heavy ion collisions are computed by combining a classical Yang-Mills description of the early time Glasma flow with the subsequent relativistic viscous hydrodynamic evolution of matter through the quark-gluon plasma and hadron gas phases. The Glasma dynamics, as realized in the impact parameter dependent Glasma (IP-Glasma) model, takes into account event-by-event geometric fluctuations in nucleon positions and intrinsic subnucleon scale color charge fluctuations; the preequilibrium flow of matter is then matched to the music algorithm describing viscous hydrodynamic flow and particle production at freeze-out. The IP-Glasma+MUSIC model describes well both transverse momentum dependent and integrated v_{n} data measured at the Large Hadron Collider and the Relativistic Heavy Ion Collider. The model also reproduces the event-by-event distributions of v_{2}, v_{3} and v_{4} measured by the ATLAS Collaboration. The implications of our results for better understanding of the dynamics of the Glasma and for the extraction of transport properties of the quark-gluon plasma are outlined.Physical Review Letters 01/2013; 110(1):012302. · 7.37 Impact Factor -
Article: Initial state fluctuations and higher harmonic flow in heavy-ion collisions
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ABSTRACT: A framework combining Yang-Mills dynamics of the pre-equilibrium glasma with relativistic viscous hydrodynamic evolution of the quark-gluon plasma and hadron gas phases is presented. Event-by-event fluctuations of nucleon positions and color charges are taken into account, leading to negative binomial fluctuations of gluon multiplicities. Experimental anisotropic flow coefficients v2-v5 of charged hadron distributions in heavy-ion collisions at the Large Hadron Collider are well described. Furthermore, event-by-event distributions of v2, v3 and v4 measured by the ATLAS collaboration are reproduced.10/2012; -
Article: MUSIC with the UrQMD Afterburner
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ABSTRACT: As RHIC is entering the precision measurement era and the LHC is producing a copious amount of new data, the role of 3+1D event-by-event viscous hydrodynamics is more important than ever to understand the bulk data as well as providing the background for hard probes. For more meaningful comparison with the experimental data, it is also important that hydrodynamics be coupled to the hadronic afterburner. In this proceeding we report on preliminary results of coupling MUSIC with UrQMD.10/2012; -
Article: Elliptic and triangular flows in 3+1D viscous hydrodynamics with fluctuating initial conditions
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ABSTRACT: Using a 3+1D viscous hydrodynamic model of relativistic heavy ion collisions, we show that event-by-event fluctuation is essential in understanding the quark–gluon plasma produced in collisions at the RHIC and the LHC.Journal of Physics G Nuclear and Particle Physics 11/2011; 38(12):124169. · 4.18 Impact Factor -
Article: MARTINI event generator for heavy quarks: Initialization, parton evolution, and hadronization
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ABSTRACT: We present additions to the MARTINI event generator for examining heavy quarks and quarkonia in heavy-ion collisions. All stages of a heavy-ion collision affect the observables associated with heavy quarks: the initial phase space of the heavy quarks are sampled with pythia8.1, the heavy quarks are evolved using Langevin dynamics and a 3+1-dimensional hydrodynamical description of the heavy-ion collision, and are fragmented and hadronized using a modified version of the color evaporation model that takes into account nontrivial evolution in position space, as well as the possibility of recombinant quarkonium production in heavy-ion collisions. We use this to re-examine the production of quarkonium at the Relativistic Heavy Ion Collider (RHIC), and anticipating vertex detection we predict yields of Bc mesons at RHIC and the Large Hadron Collider.Phys. Rev. C. 11/2011; 86(3). -
Article: Higher flow harmonics from (3+1)D event-by-event viscous hydrodynamics
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ABSTRACT: We present event-by-event viscous hydrodynamic calculations of the anisotropic flow coefficients v_2 to v_5 for heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC). We study the dependence of different flow harmonics on shear viscosity and the morphology of the initial state. v_3 and higher flow harmonics exhibit a particularly strong dependence on both the initial granularity and shear viscosity. We argue that a combined analysis of all available flow harmonics will allow to determine eta/s of the quark gluon plasma precisely. Presented results strongly hint at a value (eta/s)_QGP < 2/4pi at RHIC. Furthermore, we demonstrate the effect of shear viscosity on pseudo-rapidity spectra and the mean transverse momentum as a function of rapidity.09/2011; -
Article: Monte-Carlo simulation of jets in heavy-ion collisions
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ABSTRACT: We present Monte-Carlo simulations of jet evolution in lead-lead collisions at the Large Hadron Collider (LHC) at CERN focusing on the dijet asymmetry measured by the ATLAS and CMS collaborations. In the simulation, hard partons are interacting with the hydrodynamical background medium, undergoing radiative and collisional processes. The measured dijet asymmetry is well described by the simulation and is hence consistent with partonic energy loss in a hot, strongly-interacting medium.09/2011; -
Article: Monte-Carlo Simulation of Hard Probes in Heavy-Ion Collisions
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ABSTRACT: Results from the Modular Algorithm for Relativistic Treatment of heavy IoN Interactions (MARTINI) are presented. This comprehensive event generator for the hard and penetrating probes in high energy nucleus-nucleus collisions employs a time evolution model for the soft background, PYTHIA 8.1 and the McGill-AMY parton evolution scheme including radiative as well as elastic processes. It generates full event configurations in the high pT region, taking into account thermal QCD and QED effects as well as effects of the evolving medium.Journal of Physics Conference Series 09/2011; 312(1):012003. -
Article: Viscous photons in relativistic heavy ion collisions
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ABSTRACT: Theoretical studies of the production of real thermal photons in relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are performed. The space-time evolution of the colliding system is modelled using MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and viscous versions. The inclusive spectrum and its azimuthal angular anisotropy are studied separately, and the relative contributions of the different photon sources are highlighted. It is shown that the photon v2 coefficient is especially sensitive to the details of the microscopic dynamics like the equation of state, the ratio of shear viscosity over entropy density, eta/s, and to the morphology of the initial state.09/2011; -
Article: Dijet asymmetry at the energies available at the CERN Large Hadron Collider
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ABSTRACT: The martini numerical simulation allows for direct comparison of theoretical model calculations and the latest results for dijet asymmetry from the ATLAS and CMS collaborations. In this paper, partons are simulated as undergoing radiative and collisional processes throughout the evolution of central lead-lead collisions at the Large Hadron Collider. Using hydrodynamical background evolution determined by a simulation which fits well with the data on charged particle multiplicities from ALICE and a value of αs≈0.25–0.3, the dijet asymmetry is found to be consistent with partonic energy loss in a hot, strongly interacting medium.Phys. Rev. C. 08/2011; 84(2). -
Article: A holographic model for large N thermal QCD
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ABSTRACT: We summarize the dual gravity description for a thermal gauge theory, reviewing the key features of our holographic model of large N QCD and elaborating on some new results.The theory has matter in the fundamental representation and the gauge coupling runs logarithmically with energy scale at low energies. At the highest energies the theory becomes approximately scale invariant, much like what we would expect for large N QCD although not with asymptotic freedom. In this limit the theory has a gravity dual captured by an almost classical supergravity description with a controlled quantum behavior, such that by renormalizing the supergravity action, we can compute the stress tensor of the dual gauge theory. From the stress tensor we obtain the shear viscosity and the entropy of the medium at a temperature T, and the violation of the bound for the viscosity to the entropy ratio is then investigated. By considering dynamics of open strings in curved spacetime described by the supergravity limit, we compute the drag and diffusion coefficients for a heavy parton traversing the thermal medium. It is shown that both coefficients have a logarithmic dependence on momentum, consistent with pQCD expectations. Finally, we study the confinement/deconfinement mechanism for quarks by analyzing open strings in the presence of the flavor seven branes. We find linear confinement of quarks at low temperatures, while at high temperatures the quarkonium states melt, a behavior consistent with the existence of a deconfined phase.08/2011; -
Article: Photons at RHIC: The role of viscosity and of initial state fluctuations
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ABSTRACT: We study real photons produced in heavy ion collisions at RHIC, and we calculate their spectrum and its azimuthal momentum anisotropy. The photons from a variety of sources are included, and the interplay and the time-evolution of those sources are modelled in a full 3D hydrodynamic simulation. We quantify the v_2 of thermal photons produced in ideal and viscous fluids, and the consequences of using different initial conditions are explored.07/2011; -
Article: Comparison of Jet Quenching Formalisms for a Quark-Gluon Plasma "Brick"
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ABSTRACT: We review the currently available formalisms for radiative energy loss of a high-momentum parton in a dense strongly interacting medium. The underlying theoretical framework of the four commonly used formalisms is discussed and the differences and commonalities between the formalisms are highlighted. A quantitative comparison of the single gluon emission spectra as well as the energy loss distributions is given for a model system consisting of a uniform medium with a fixed length of L=2 fm and L=5 fm (the `Brick'). Sizable quantitative differences are found. The largest differences can be attributed to specific approximations that are made in the calculation of the radiation spectrum.06/2011; -
Article: Anisotropic flow in sqrt(s)=2.76 TeV Pb+Pb collisions at the LHC
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ABSTRACT: The results on elliptic flow in sqrt(s)=2.76 TeV Pb+Pb collisions at the Large Hadron Collider (LHC) reported by the ALICE collaboration are remarkably similar to those for sqrt(s)=200 GeV gold-gold collisions at the Relativistic Heavy Ion Collider (RHIC). This result is surprising, given the expected longer lifetime of the system at the higher collision energies. We show that it is nevertheless consistent with 3+1 dimensional viscous event-by-event hydrodynamic calculations, and demonstrate that elliptic flow at both RHIC and LHC is built up mostly within the first 5 fm/c of the evolution. We conclude that an "almost perfect liquid" is produced in heavy-ion collisions at the LHC. Furthermore, we present predictions for triangular flow as a function of transverse momentum for different centralities.02/2011; -
Article: Hydrodynamic evolution and jet energy loss in Cu+Cu collisions
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ABSTRACT: We present results from a hybrid description of Cu+Cu collisions using 3+1 dimensional hydrodynamics (MUSIC) for the bulk evolution and a Monte-Carlo simulation (MARTINI) for the evolution of high momentum partons in the hydrodynamical background. We explore the limits of this description by going to small system sizes and determine the dependence on different fractions of wounded nucleon and binary collisions scaling of the initial energy density. We find that Cu+Cu collisions are well described by the hybrid description at least up to 20% central collisions.01/2011; -
Article: Elliptic and triangular flow in event-by-event D=3+1 viscous hydrodynamics.
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ABSTRACT: We present results for the elliptic and triangular flow coefficients v(2) and v(3) in Au+Au collisions at √s=200 AGeV using event-by-event D=3+1 viscous hydrodynamic simulations. We study the effect of initial state fluctuations and finite viscosities on the flow coefficients v(2) and v(3) as functions of transverse momentum and pseudorapidity. Fluctuations are essential to reproduce the measured centrality dependence of elliptic flow. We argue that simultaneous measurements of v(2) and v(3) can determine η/s more precisely.Physical Review Letters 01/2011; 106(4):042301. · 7.37 Impact Factor -
Article: Bulk spectral functions in single and multiscalar gravity duals
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ABSTRACT: We examine two-point correlation functions involving the trace of the energy-momentum tensor in five-dimensional dual gravity theories supported by one or more scalar fields. A prescription for determining bulk channel spectral functions is developed. This prescription generalizes previous work which centered on one scalar field. As an application of these techniques, we investigate the bulk spectral function and corresponding sum rule in the Chamblin-Reall background. We show that, when expressed in terms of the beta function, the sum rule for the Chamblin-Reall background can be written in a form similar to the sum rule in Yang-Mills theory.Phys. Rev. D. 12/2010; 82(12). -
Article: Shear spectral sum rule in a nonconformal gravity dual
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ABSTRACT: A sum rule which relates a stress-energy tensor correlator to thermodynamic functions is examined within the context of a simple nonconformal gravity dual. Such a sum rule was previously derived using AdS/CFT for conformal N=4 supersymmetric Yang-Mills theory, but we show that it does not generalize to the nonconformal theory under consideration. We provide a generalized sum rule and numerically verify its validity. A useful by-product of the calculation is the computation of the spectral density in a strongly coupled nonconformal theory. Qualitative features of the spectral densities and implications for lattice measurements of transport coefficients are discussed.Phys. Rev. D. 11/2010; 82(10). -
Article: Bulk spectral functions in single and multi-scalar gravity duals
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ABSTRACT: We examine two point correlation functions involving the trace of the energy momentum tensor in five dimensional gravity dual theories supported by one or more scalar fields. A prescription for determining bulk channel spectral functions is developed. This prescription generalizes previous work which centered on one scalar field. As an application of these techniques, we investigate the bulk spectral function and corresponding sum rule in the Chamblin-Reall background. We show that, when expressed in terms of the beta function, the sum rule for the Chamblin-Reall background can be written in a form similar to the sum rule in Yang-Mills theory.10/2010;
Top co-authors
Top Journals
Institutions
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2001–2011
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McGill University
- Department of Physics
Montréal, Quebec, Canada
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1998–1999
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Lawrence Berkeley National Laboratory
- Nuclear Science Division
Berkeley, CA, USA -
University of Minnesota Duluth
Duluth, MN, USA
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