Hydro+Cascade, Flow, the Equation of State, Predictions and Data

A Hydro+Cascade model has been used to describe radial and elliptic flow at the SPS and successfully predicted the radial and elliptic flow measured by the both STAR and PHENIX collaborations . Furthermore, a combined description of the radial and elliptic flow for different particle species, restricts the Equation of State(EoS) and points towards an EoS with a phase transition to the Quark Gluon Plasma(QGP) .Comment: Quark Matter 2001 Procedings. Corrected Fig. 3b for all charged. Some typos fixe

Quark-Gluon Plasma - New Frontiers

As implied by organizers, this talk is not a conference summary but rather an outline of progress/challenges/``frontiers'' of the theory. Some fundamental questions addressed are: Why is sQGP such a good liquid? Do we understand (de)confinement and what do we know about ``magnetic'' objects creating it? Can we understand the AdS/CFT predictions, from the gauge theory side? Can they be tested experimentally? Can AdS/CFT duality help us understand rapid equilibration/entropy production? Can we work out a complete dynamical ``gravity dual'' to heavy ion collisions?Comment: final talk at Quark Matter 2008, Jaipur, India, Feb.200

Hard and soft probe - medium interactions in a 3D hydro+micro approach at RHIC

We utilize a 3D hybrid hydro+micro model for a comprehensive and consistent description of soft and hard particle production in ultra-relativistic heavy-ion collisions at RHIC. In the soft sector we focus on the dynamics of (multi-)strange baryons, where a clear strangeness dependence of their collision rates and freeze-out is observed. In the hard sector we study the radiative energy loss of hard partons in a soft medium in the multiple soft scattering approximation. While the nuclear suppression factor $R_{AA}$ does not reflect the high quality of the medium description (except in a reduced systematic uncertainty in extracting the quenching power of the medium), the hydrodynamical model also allows to study different centralities and in particular the angular variation of $R_{AA}$ with respect to the reaction plane, allowing for a controlled variation of the in-medium path-length.Comment: 5 pages, 4 figures, Quark Matter 2006 proceedings, to appear in Journal of Physics

Flow at the SPS and RHIC as a Quark Gluon Plasma Signature

Radial and elliptic flow in non-central heavy ion collisions can constrain the effective Equation of State(EoS) of the excited nuclear matter. To this end, a model combining relativistic hydrodynamics and a hadronic transport code(RQMD [17]) is developed. For an EoS with a first order phase transition, the model reproduces both the radial and elliptic flow data at the SPS. With the EoS fixed from SPS data, we quantify predictions at RHIC where the Quark Gluon Plasma(QGP) pressure is expected to drive additional radial and elliptic flow. Currently, the strong elliptic flow observed in the first RHIC measurements does not conclusively signal this nascent QGP pressure. Additional measurements are suggested to pin down the EoS.Comment: 4 pages, 4 figures. Revised. Included discussed of v_2 (p_t) vs. b and comparison to STAR dat

Elliptic Flow Analysis at RHIC with the Lee-Yang Zeroes Method in a Relativistic Transport Approach

The Lee-Yang zeroes method is applied to study elliptic flow ($v_2$) in Au+Au collisions at $\sqrt{s}=200A$~GeV, with the UrQMD model. In this transport approach, the true event plane is known and both the nonflow effects and event-by-event $v_2$ fluctuations exist. Although the low resolutions prohibit the application of the method for most central and peripheral collisions, the integral and differential elliptic flow from the Lee-Yang zeroes method agrees with the exact $v_2$ values very well for semi-central collisions.Comment: 4 pages, 4 figure

Evolution of mechanism of parton energy loss with transverse momentum at RHIC and LHC in relativistic collision of heavy nuclei

We analyze the suppression of particle production at large transverse momenta in ($0-5$ most) central collisions of gold nuclei at $\sqrt{s_\textrm{NN}}=$ 200 GeV and lead nuclei at $\sqrt{s_{\textrm{NN}}}=$ 2.76 TeV. Full next-to-leading order radiative corrections at ${\cal{O}}(\alpha_s^3)$, and nuclear effects like shadowing and parton energy loss are included. The parton energy loss is implemented in a simple multiple scattering model, where the partons lose an energy $\epsilon=\lambda \times dE/dx$ per collision, where $\lambda$ is their mean free path. We take $\epsilon=\kappa E$ for a treatment which is suggestive of the Bethe Heitler (BH) mechanism of incoherent scatterings, $\epsilon = \sqrt{\alpha E}$ for LPM mechanism, and $\epsilon=$ constant for a mechanism which suggests that the rate of energy loss ($dE/dx$) of the partons is proportional to total path length ($L$) of the parton in the plasma, as the formation time of the radiated gluon becomes much larger than $L$. We find that while the BH mechanism describes the nuclear modification factor $R_{\textrm{AA}}$ for $p_T \leq$ 5 GeV/$c$ (especially at RHIC energy), the LPM and more so the constant $dE/dx$ mechanism provides a good description at larger $p_T$. This confirms the earlier expectation that the energy loss mechanism for partons changes from BH to LPM for $p_T \ge \lambda$, where $\lambda \approx$ 1 fm and $\approx$ 1 GeV$^2$ is the average transverse kick-squared received by the parton per collision. The energy loss per collision at the $\sqrt{s_\textrm{NN}}$ =2.76 TeV is found to be about twice of that at 0.2 TeV.Comment: Discussion expanded, additional references added, 14 pages, 6 figures, To appear in Journal of Physics

Hydrodynamics at RHIC -- how well does it work, where and how does it break down?

I review the successes and limitations of the ideal fluid dynamic model in describing hadron emission spectra from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC).Comment: 8 pages, 4 figures. Invited talk presented at Strange Quark Matter 2004 (Cape Town, Sep. 15-20, 2004). Proceedings to appear in Journal of Physics

Mach Cones in Quark Gluon Plasma

The experimental azimuthal dihadron distributions at RHIC show a double peak structure in the away side ($\Delta \phi = \pi \pm 1.2$ rad.) for intermediate $p_t$ particles. A variety of models have appeared trying to describe this modification. We will review most of them, with special emphasis in the Conical Flow scenario in which the observed shape is a consequence of the emission of sound by a supersonic high momentum particle propagating in the Quark Gluon Plasma.Comment: 8 pages, 3 figures, Invited plenary talk given at the 19th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2006 (QM 2006), Shanghai, China, 14-20 Nov 200

Nuclear suppression of heavy quark production at forward rapidities in relativistic heavy ion collisions

We calculate nuclear suppression $R_{AA}$ of heavy quarks produced from the initial fusion of partons in nucleus-nucleus collisions at RHIC and LHC energies. We take the shadowing as well as the energy loss suffered by them while passing through Quark Gluon Plasma into account. We obtain results for charm and bottom quarks at several rapidities using different mechanisms for energy loss, to see if we can distinguish between them.Comment: 21 pages including 13 figures. To appear in J. Phys.

Examine the species and beam-energy dependence of particle spectra using Tsallis Statistics

Tsallis Statistics was used to investigate the non-Boltzmann distribution of particle spectra and their dependence on particle species and beam energy in the relativistic heavy-ion collisions at SPS and RHIC. Produced particles are assumed to acquire radial flow and be of non-extensive statistics at freeze-out. J/psi and the particles containing strangeness were examined separately to study their radial flow and freeze-out. We found that the strange hadrons approach equilibrium quickly from peripheral to central A+A collisions and they tend to decouple earlier from the system than the light hadrons but with the same final radial flow. These results provide an alternative picture of freeze-outs: a thermalized system is produced at partonic phase; the hadronic scattering at later stage is not enough to maintain the system in equilibrium and does not increase the radial flow of the copiously produced light hadrons. The J/psi in Pb+Pb collisions at SPS is consistent with early decoupling and obtains little radial flow. The J/psi spectra at RHIC are also inconsistent with the bulk flow profile.Comment: 12 pages, 4 figures, added several references and some clarifications et