QGP viscosity at RHIC and the LHC - a 2012 status report

In this article, we briefly review the recent progress related to extracting the quark-gluon plasma (QGP) specific shear viscosity from the flow data measured at Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC).Comment: 8 pages, 2 figures, proceedings of Quark Matter 2012, August 13-18, Washington D.C., US

Chemical and thermal freeze-out of identified hadrons at the LHC

This proceeding briefly summarizes our recent VISHNU hybrid model investigations on the chemical and thermal freeze-out of various hadrons species in 2.76 A TeV Pb+Pb collisions. Detailed analysis on the evolution of particle yields and the last elastic collisions distributions during the hadronic evolution reveals that the two multi-strange hadrons, $\Xi$ and $\Omega$, experience early chemical and thermal freeze-out when compared with other hadron species.Comment: 4 pages, 3 figures, SQM2015 proceedin

Universal scaling of non-equilibrium critical fluctuations from Langevin dynamics of model A

Within the framework of the Kibble-Zurek Mechanism, we investigate the universal behavior of the non-equilibrium critical fluctuations, using the Langevin dynamics of model A. With properly located typical time, length and angle scales, \tau_{\mbox{KZ}}, l_{\mbox{KZ}}, and \theta_{\mbox{KZ}}, the constructed functions \bar{f}_n((\tau-\tau_c)/\tau_{\mbox{KZ}},\theta_{\mbox{KZ}}) (n=1...4) for the cumulants of the sigma field show universal behavior near the critical point, which are independent from some non-universal factors, such as the relaxation time or the evolution trajectory.Comment: 6 pages, 3 figures, CPOD 2017 proceeding

Dynamical fluctuations in critical regime and across the 1st order phase transition

In this proceeding, we study the dynamical evolution of the sigma field within the framework of Langevin dynamics. We find that, as the system evolves in the critical regime, the magnitudes and signs of the cumulants of sigma field, $C_{3}$ and $C_{4}$, can be dramatically different from the equilibrated ones due to the memory effects near $T_c$. For the dynamical evolution across the 1st order phase transition boundary, the supercooling effect leads the sigma field to be widely distributed in the thermodynamical potential, which largely enhances the cumulants $C_3, \ C_4$, correspondingly.Comment: 4 pages, 2 figures, proceedings for Quark Matter 201

Causal Viscous Hydrodynamics for Relativistic Heavy Ion Collisions

The viscosity of the QGP is a presently hotly debated subject. Since its computation from first principles is difficult, it is desirable to try to extract it from experimental data. Viscous hydrodynamics provides a tool that can attack this problem and which may work in regions where ideal hydrodynamics begins to fail. This thesis focuses on viscous hydrodynamics for relativistic heavy ion collisions. We first review the 2nd order viscous equations obtained from different approaches, and then report on the work of the Ohio State University group on setting up the equations for causal viscous hydrodynamics in 2+1 dimensions and solving them numerically for central and noncentral Cu+Cu and Au+Au collisions at RHIC energies and above. We discuss shear and bulk viscous effects on the hydrodynamic evolution of entropy density, temperature, collective flow, and flow anisotropies, and on the hadron multiplicity, single particle spectra and elliptic flow. Viscous entropy production and its influence on the centrality dependence of hadron multiplicities and the multiplicity scaling of eccentricity-scaled elliptic flow are studied in viscous hydrodynamics and compared with experimental data. The dynamical effects of using different versions of the Israel-Stewart second order formalism for causal viscous fluid dynamics are discussed, resolving some of the apparent discrepancies between early results reported by different groups. Finally, we assess the present status of constraining the shear viscosity to entropy ratio of the hot and dense matter created at RHIC.Comment: Ph.D thesis (The Ohio State University, 2009; Advisor: U. Heinz), a printer friendly version with tight lines (110 pages

Enhancements of high order cumulants across the 1st order phase transition boundary

In this proceeding, we investigate the dynamical evolution of the $\sigma$ field with a trajectory across the 1st order phase transition boundary, using Langevin dynamics from the linear sigma model. We find the high order cumulants of the $\sigma$ field are largely enhanced during the dynamical evolution, compared with the equilibrium values, due to the supercooling effect of the first order phase transition.Comment: 4 pages, 2 figures, SQM proceeding, with minor change

Collective flow and hydrodynamics in large and small systems at the LHC

In this article, we briefly review the recent progress on collective flow and hydrodynamics in large and small systems at the Large Hadron Collider (LHC), which includes the following topics: extracting the QGP viscosity from the flow data, initial state fluctuations and final state correlations in 2.76 A TeV Pb--Pb collisions, correlations and collective flow in high energy p--Pb and p--p collisions.Comment: 43 pages, 15 figures, Invited Review for Nuclear Science and Technique