Tsunamis, Viscosity and the HBT Puzzle

The equation of state and bulk and shear viscosities are shown to be able to affect the transverse dynamics of a central heavy ion collision. The net entropy, along with the femtoscopic radii are shown to be affected at the 10-20% level by both shear and bulk viscosity. The degree to which these effects help build a tsunami-like pulse is also discussed.Comment: Contribution to SQM 2007 in Levoca, Slovaki

Elliptic and triangular flow of identified particles at ALICE

We report on the first measurements of elliptic and triangular flow for charged pions, kaons and anti-protons in lead-lead collisions at 2.76 TeV measured with the ALICE detector at the LHC. We compare the observed mass splitting of differential elliptic flow at LHC energies to RHIC measurements at lower energies and theory predictions. We test the quark coalescence picture with the quark number scaling of elliptic and triangular flow.Comment: 4 pages, 5 figures, Quark Matter 2011 conference proceeding

Dissipative hydrodynamics and heavy ion collisions

Space-time evolution and subsequent particle production from minimally viscous ($\eta/s$=0.08) QGP fluid is studied using the 2nd order Israel-Stewart's theory of dissipative relativistic fluid. Compared to ideal fluid, energy density or temperature evolves slowly in viscous dynamics. Particle yield at high $p_T$ is increased. Elliptic flow on the other hand decreases in viscous dynamics. Minimally viscous QGP fluid found to be consistent with a large number of experimental data.Comment: 8 pages, 13 figures. Revised version of the invited talk at the 20th International conference on Ultra-Relativistic Nucleus Nucleus collisions (Quark Matter 2008), Feb. 4-10, 2008, Jaipur, Indi

Feeding of the elliptic flow by hard partons

We propose that in nuclear collisions at the LHC the elliptic flow may get a contribution from leading hard and semihard partons which deposit energy and momentum into the hydrodynamic bulk medium. The crucial effect is that these partons induce wakes which interact and merge if they come together. The contribution to the integrated elliptic flow is estimated with the help of a toy model to about 25% of the observed value and shows strong event-by-event fluctuations.Comment: 9 pages, 3 figure

Centrality dependence of elliptic flow and QGP viscosity

In the Israel-Stewart's theory of second order hydrodynamics, we have analysed the recent PHENIX data on charged particles elliptic flow in Au+Au collisions. PHENIX data demand more viscous fluid in peripheral collisions than in central collisions. Over a broad range of collision centrality (0-10%- 50-60%), viscosity to entropy ratio ($\eta/s$) varies between 0-0.17.Comment: Final version to be publiashed in J. Phys. G. 8 pages, 6 figures and 3 table

Elliptic Flow: A Brief Review

One of the fundamental questions in the field of subatomic physics is what happens to matter at extreme densities and temperatures as may have existed in the first microseconds after the Big Bang and exists, perhaps, in the core of dense neutron stars. The aim of heavy-ion physics is to collide nuclei at very high energies and thereby create such a state of matter in the laboratory. The experimental program started in the 1990's with collisions made available at the Brookhaven Alternating Gradient Synchrotron (AGS), the CERN Super Proton Synchrotron (SPS) and continued at the Brookhaven Relativistic Heavy-Ion Collider (RHIC) with maximum center of mass energies of 4.75, 17.2 and 200 GeV respectively. Collisions of heavy-ions at the unprecedented energy of 2.76 TeV have recently become available at the LHC collider at CERN. In this review I will give a brief introduction to the physics of ultra-relativistic heavy-ion collisions and discuss the current status of elliptic flow measurements.Comment: version accepted by NJ

Quark-Gluon Plasma at RHIC and the LHC: Perfect Fluid too Perfect?

Relativistic heavy ion collisions have reached energies that enable the creation of a novel state of matter termed the quark-gluon plasma. Many observables point to a picture of the medium as rapidly equilibrating and expanding as a nearly inviscid fluid. In this article, we explore the evolution of experimental flow observables as a function of collision energy and attempt to reconcile the observed similarities across a broad energy regime in terms of the initial conditions and viscous hydrodynamics. If the initial spatial anisotropies are very similar for all collision energies from 39 GeV to 2.76 TeV, we find that viscous hydrodynamics might be consistent with the level of agreement for v2 of unidentified hadrons as a function of pT . However, we predict a strong collision energy dependence for the proton v2(pT). The results presented in this paper highlight the need for more systematic studies and a re-evaluation of previously stated sensitivities to the early time dynamics and properties of the medium.Comment: 11 pages, 9 figures, submitted to the New Journal of Physics focus issue "Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD Plasmas

Flow in heavy-ion collisions - Theory Perspective

I review recent developments in the field of relativistic hydrodynamics and its application to the bulk dynamics in heavy-ion collisions at the Relativistic Heavy- Ion Collider (RHIC) and the Large Hadron Collider (LHC). In particular, I report on progress in going beyond second order relativistic viscous hydrodynamics for conformal fluids, including temperature dependent shear viscosity to entropy density ratios, as well as coupling hydrodynamic calculations to microscopic hadronic rescattering models. I describe event-by-event hydrodynamic simulations and their ability to compute higher harmonic flow coefficients. Combined comparisons of all harmonics to recent experimental data from both RHIC and LHC will potentially allow to determine the desired details of the initial state and the medium properties of the quark-gluon plasma produced in heavy-ion collisions.Comment: 8 pages, Invited plenary talk at the 22nd International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2011), May 23-28 2011, Annecy, Franc

Pion electromagnetic form factor at finite temperature

Temperature effects on the electromagnetic couplings of pions in hot hadronic matter are studied with an effective chiral Lagrangian. We show that the Ward-Takahashi identity is satisfied at non-zero temperature in the soft pion limit. The in-medium electromagnetic form factor of the pion is obtained in the time-like region and shown to be reduced in magnitude, especially near the vector-meson resonance region. Finally, we discuss the consequences of this medium effect on dilepton production from hot hadronic matter.Comment: 29 pages (LaTex) + 11 figure

Anisotropic flow at the LHC measured with the ALICE detector

The ALICE detector at the LHC recorded first Pb-Pb collisions at 2.76 TeV in November and December of 2010. We report on the measurements of anisotropic flow for charged and identified particles. From the comparison with measurements at lower energies and with model predictions we find that the system created at these collision energies is described well by hydrodynamical model calculations and behaves like an almost perfect fluid.Comment: 8 pages, 16 figures, plenary talk at Quark Matter 2011, May 23rd-28th 2011, Annecy, Franc