Evolution of elliptic and triangular flow as a function of beam energy in a hybrid model

Elliptic flow has been one of the key observables for establishing the finding of the quark-gluon plasma (QGP) at the highest energies of Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). As a sign of collectively behaving matter, one would expect the elliptic flow to decrease at lower beam energies, where the QGP is not produced. However, in the recent RHIC beam energy scan, it has been found that the inclusive charged hadron elliptic flow changes relatively little in magnitude in the energies between 7.7 and 39 GeV per nucleon-nucleon collision. We study the collision energy dependence of the elliptic and triangular flow utilizing a Boltzmann + hydrodynamics hybrid model. Such a hybrid model provides a natural framework for the transition from high collision energies, where the hydrodynamical description is essential, to smaller energies, where the hadron transport dominates. This approach is thus suitable to investigate the relative importance of these two mechanisms for the production of the collective flow at different values of beam energy. Extending the examined range down to 5 GeV per nucleon-nucleon collision allows also making predictions for the CBM experiment at FAIR.Comment: 8 pages, 3 figures. Talk in FAIRNESS 2013 workshop, September 201

The form of the elastic energy loss probability distribution in a static medium

We examine the probability distributions P(E,t) of the energy of a hard parton traveling in a partonic medium of constant density for a time t while undergoing elastic 2-to-2 pQCD interactions using a Monte-Carlo model. The form of these distributions is found to be non-Gaussian, confirming results by other groups with similarly detailed models and challenging the validity of the widely used diffusion approximation in elastic energy loss modeling.Comment: 4 pages, 5 figure

Collision Energy Evolution of Elliptic and Triangular Flow in a Hybrid Model

While the existence of a strongly interacting state of matter, known as 'quark-gluon plasma' (QGP), has been established in heavy ion collision experiments in the past decade, the task remains to map out the transition from the hadronic matter to the QGP. This is done by measuring the dependence of key observables (such as particle suppression and elliptic flow) on the collision energy of the heavy ions. This procedure, known as 'beam energy scan', has been most recently performed at the Relativistic Heavy Ion Collider (RHIC). Utilizing a Boltzmann+hydrodynamics hybrid model, we study the collision energy dependence of initial state eccentricities and the final state elliptic and triangular flow. This approach is well suited to investigate the relative importance of hydrodynamics and hadron transport at different collision energies.Comment: 6 pages, 6 figures. Talk given in CPOD 2013 - 8th International Workshop on Critical Point and Onset of Deconfinement, March 11-15, Napa, C

The beam energy dependence of collective flow in heavy ion collisions

The major goals of heavy ion research are to explore the phase diagram of quantum chromodynamics (QCD) and to investigate the properties of the quark gluon plasma (QGP), a new state of matter created at high temperatures and/or densities. Collective anisotropic flow is one of the most promising observables to gain insights about the properties of the system created in relativistic heavy ion reactions. The current status of the beam energy dependence of the first three Fourier coefficients of the azimuthal distribution of the produced particles $v_1$ to $v_3$ within hybrid transport plus hydrodynamics approaches are summarized.Comment: 11 pages, 7 figures, Proceedings for CPOD 2014, Bielefeld, German

Monte Carlo Simulation for Elastic Energy Loss of Hard Partons in a Hydrodynamical Background

We have developed a Monte Carlo simulation describing the $2 \rightarrow 2$ scatterings of perturbatively produced, non-eikonally propagating high-energy partons with the quarks and gluons of the expanding QCD medium created in ultrarelativistic heavy ion collisions. The partonic scattering rates are computed in leading-order perturbative QCD (pQCD), while three different hydrodynamical scenarios are used to model the strongly interacting medium. We compare our results and tune the model with the neutral pion suppression observed in $\sqrt{s_{NN}}=200$ GeV Au+Au collisions at the BNL-RHIC. We find the incoherent nature of elastic energy loss incompatible with the measured angular dependence of the suppression. The effects of the initial state density fluctuations of the bulk medium are found to be small. Also the extrapolation from RHIC to the LHC is discussed.Comment: 4 pages, 2 figures. Talk given at Quark Matter 2011 conference, 23-28 May 2011, Annecy, Franc

Elastic energy loss with respect to the reaction plane in a Monte-Carlo model

We present a computation of $\pi^0$ nuclear modification factor with respect to the reaction plane in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV, based on a Monte-Carlo model of elastic energy loss of hard partons traversing the bulk hydrodynamical medium created in ultrarelativistic heavy-ion collisions. We find the incoherent nature of elastic energy loss incompatible with the measured data.Comment: 5 pages, 2 figure

Investigating the collision energy dependence of η\eta/s in RHIC beam energy scan using Bayesian statistics

We determine the probability distributions of shear viscosity over the entropy density ratio $\eta/s$ in Au+Au collisions at $\sqrt{s_{NN}}=19.6, 39$, and $62.4$ GeV, using Bayesian inference and Gaussian process emulators for a model-to-data statistical analysis that probes the full input parameter space of a transport+viscous hydrodynamics hybrid model. We find the most likely value of $\eta/s$ to be larger at smaller $\sqrt{s_{NN}}$, although the uncertainties still allow for a constant value between 0.10 and 0.15 for the investigated collision energy range.Comment: 44 pages, 34 figures. Submitted to Phys. Rev.