Hannah Petersen

Triangular flow in event-by-event ideal hydrodynamics in Au+Au collisions at √SNN = 200A GeV

The first calculation of triangular flow v{sub 3} in Au+Au collisions at {radical}(s{sub NN})=200A GeV from an event-by-event (3+1)d transport+hydrodynamics hybrid approach is presented. As a response to the initial triangularity {epsilon}{sub 3} of the collision zone, v{sub 3} is computed in a similar way to the standard event-plane analysis for elliptic flow v{sub 2}. It is found that the triangular flow exhibits weak centrality dependence and is roughly equal to elliptic flow in most central collisions. We also explore the transverse momentum and rapidity dependence of v{sub 2} and v{sub 3} for charged particles as well as identified particles. We conclude that an event-by-event treatment of the ideal hydrodynamic evolution starting with realistic initial conditions generates the main features expected for triangular flow.

Translation of collision geometry fluctuations into momentum anisotropies in relativistic heavy-ion collisions

We develop a systematic framework for the study of the initial collision geometry fluctuations in relativistic heavy-ion collisions and investigate how they evolve through different stages of the fireball history and translate into final-particle momentum anisotropies. We find in our event-by-event analysis that only the few lowest momentum anisotropy parameters survive after the hydrodynamical evolution of the system. The geometry of the produced medium is found to be affected by the pre-equilibrium evolution of the medium and the thermal smearing of the discretized event-by-event initial conditions, both of which tend to smear out the spatial anisotropies. We find such effects to be more prominent for higher moments than for lower moments. The correlations between odd and even spatial anisotropy parameters during the pre-equilibrium expansion are quantitatively studied and found to be small. Our study provides a theoretical foundation for the understanding of initial-state fluctuations and the collective expansion dynamics in relativistic heavy-ion collisions.

Initial State Fluctuations and Final State Correlations in Relativistic Heavy-Ion Collisions

We review the phenomenology and theory of bulk observables in ultra-relativistic heavy-ion collisions, focusing on recent developments involving event-by-event fluctuations in the initial stages of a heavy-ion collision, and how they manifest in observed correlations. We first define the relevant observables and show how each measurement is related to underlying theoretical quantities. Then we review the prevailing picture of the various stages of a collision, including the state-of-the-art modeling of the initial stages of a collision and subsequent hydrodynamic evolution, as well as hadronic scattering and freeze-out in the later stages. We then discuss the recent results that have shaped our current understanding and identify the challenges that remain. Finally, we point out open issues and the potential for progress in the field.

Particlization in hybrid models

In hybrid models, which combine hydrodynamical and transport approaches to describe different stages of heavy-ion collisions, conversion of fluid to individual particles, particlization, is a non-trivial technical problem. We describe in detail how to find the particlization hypersurface in a 3+1 dimensional model, and how to sample the particle distributions evaluated using the Cooper-Frye procedure to create an ensemble of particles as an initial state for the transport stage. We also discuss the role and magnitude of the negative contributions in the Cooper-Frye procedure.

Estimation of the shear viscosity at finite net-baryon density from

Hybrid approaches based on relativistic hydrodynamics and transport theory have been successfully applied for many years for the dynamical description of heavy ion collisions at ultrarelativistic energies. In this work a new viscous hybrid model employing the hadron transport approach UrQMD for the early and late non-equilibrium stages of the reaction, and 3+1 dimensional viscous hydrodynamics for the hot and dense quark-gluon plasma stage is introduced. This approach includes the equation of motion for finite baryon number, and employs an equation of state with finite net-baryon density to allow for calculations in a large range of beam energies. The parameter space of the model is explored, and constrained by comparison with the experimental data for bulk observables from SPS and the phase I beam energy scan at RHIC. The favored parameter values depend on energy, but allow to extract the effective value of the shear viscosity coefficient over entropy density ratio

A+A

\eta/s

collision data at

in the fluid phase for the whole energy region under investigation. The estimated value of

\sqrt{s_\mathrm{NN}} = 7.7-200

\eta/s

GeV

increases with decreasing collision energy, which may indicate that

Decorrelation of anisotropic flow along the longitudinal direction

\eta/s