Higher Flow Harmonics in Heavy Ion Collisions from STAR

We report STAR measurements relating to higher flow harmonics including the centrality dependence of two- and four-particle cumulants for harmonics 1 to 6. Two-particle correlation functions vs. \Delta\eta and \Delta\phi are presented for pT and number correlations. We find the power spectra (Fourier Transforms of the correlation functions) for central collisions drop quickly for higher harmonics. The \Delta\eta dependence of v3{2}2 and the pT and centrality dependence of v2 and v3 are studied. Trends are conistent with expectations from models including hot-spots in the initial energy density and an expansion phase. We also present v3 and v2{2}2 - v2{4}2 vs. \surdsNN .Comment: 8 pages. Conference proceedings for Quark Matter 201

Ekpyrosis and inflationary dynamics in heavy ion collisions: the role of quantum fluctuations

We summarize recent significant progress in the development of a first-principles formalism to describe the formation and evolution of matter in very high energy heavy ion collisions. The key role of quantum fluctuations both before and after a collision is emphasized. Systematic computations are now feasible to address early time dynamics essential to quantifying properties of strongly interacting quark-gluon matter.Comment: Talk by R.V. at Quark Matter 2011, Annecy, France, May 23-28, 2011. LaTex, 4 pages; v2, final version to appear in J. Phys.

Constraining the initial state granularity with bulk observables in Au+Au collisions at sNN=200\sqrt{s_{\rm NN}}=200 GeV

In this paper we conduct a systematic study of the granularity of the initial state of hot and dense QCD matter produced in ultra-relativistic heavy-ion collisions and its influence on bulk observables like particle yields, $m_T$ spectra and elliptic flow. For our investigation we use a hybrid transport model, based on (3+1)d hydrodynamics and a microscopic Boltzmann transport approach. The initial conditions are generated by a non-equilibrium hadronic transport approach and the size of their fluctuations can be adjusted by defining a Gaussian smoothing parameter $\sigma$. The dependence of the hydrodynamic evolution on the choices of $\sigma$ and $t_{start}$ is explored by means of a Gaussian emulator. To generate particle yields and elliptic flow that are compatible with experimental data the initial state parameters are constrained to be $\sigma=1$ fm and $t_{\rm start}=0.5$ fm. In addition, the influence of changes in the equation of state is studied and the results of our event-by-event calculations are compared to a calculation with averaged initial conditions. We conclude that even though the initial state parameters can be constrained by yields and elliptic flow, the granularity needs to be constrained by other correlation and fluctuation observables.Comment: 14 pages, 8 figures, updated references, version to appear in J. Phys.

A systematic study of the sensitivity of triangular flow to the initial state fluctuations in relativistic heavy-ion collisions

Experimental data from the Relativistic Heavy Ion Collider (RHIC) suggests that the quark gluon plasma behaves almost like an ideal fluid. Due to its short lifetime, many QGP properties can only be inferred indirectly through a comparison of the final state measurements with transport model calculations. Among the current phenomena of interest are the interdependencies between two collective flow phenomena, elliptic and triangular flow. The former is mostly related to the initial geometry and collective expansion of the system whereas the latter is sensitive to the fluctuations of the initial state. For our investigation we use a hybrid transport model based on the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach using an ideal hydrodynamic expansion for the hot and dense stage. Using UrQMD initial conditions for an Au-Au collision, particles resulting from a collision are mapped into an energy density distribution that is evolved event-by-event with a hydrodynamic calculation. By averaging these distributions over different numbers of events, we have studied how the granularity/smoothness of the distribution affects the initial eccentricity, the initial triangularity, and the resulting flow components. The average elliptic flow in non central collisions is not sensitive to the granularity, while triangular flow is. The triangularity might thus provide a good measure of the amount of initial state fluctuations that is necessary to reproduce the experimental data.Comment: 10 pages, 7 figure

QCD and strongly coupled gauge theories : challenges and perspectives

We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe