Elliptic flow of gluon matter in ultrarelativistic heavy-ion collisions

Employing a perturbative QCD based parton cascade we calculate the elliptic flow $v_2$ and its transverse momentum dependence $v_2(p_T)$ for the gluon matter created in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. To make comparisons with the experimental data at the BNL Relativistic Heavy Ion Collider (RHIC), parton-hadron duality is assumed. We find that whereas the integrated $v_2$ matches the experimental data, the gluon (or pion) $v_2(p_T)$ is about 20-50% smaller than the experimental data. Hadronization via gluon fragmentation and quark recombination seems to be the key to explaining the necessary jump of $v_2(p_T)$ from the partonic to the hadronic phase. We also show that the elliptic flow values moderately depend on the chosen freezeout condition, which will thus constrain the shear viscosity to the entropy density ratio of the quark gluon plasma created at RHIC.Comment: 20 pages, 7 figures, minor corrections, published versio

Energy loss in a partonic transport model including bremsstrahlung processes

A detailed investigation of the energy loss of gluons that traverse a thermal gluonic medium simulated within the perturbative QCD--based transport model BAMPS (a Boltzmann approach to multiparton scatterings) is presented in the first part of this work. For simplicity the medium response is neglected in these calculations. The energy loss from purely elastic interactions is compared to the case where radiative processes are consistently included based on the matrix element by Gunion and Bertsch. From this comparison gluon multiplication processes gg -> ggg are found to be the dominant source of energy loss within the approach employed here. The consequences for the quenching of gluons with high transverse momentum in fully dynamic simulations of Au+Au collisions at the RHIC energy of sqrt(s) = 200 AGeV are discussed in the second major part of this work. The results for central collisions as discussed in a previous publication are revisited and first results on the nuclear modification factor R_AA for non-central Au+Au collisions are presented. They show a decreased quenching compared to central collisions while retaining the same shape. The investigation of the elliptic flow v2 is extended up to non-thermal transverse momenta of 10 GeV, exhibiting a maximum v2 at roughly 4 to 5 GeV and a subsequent decrease. Finally the sensitivity of the aforementioned results on the specific implementation of the effective modeling of the Landau-Pomeranchuk-Migdal (LPM) effect via a formation time based cut-off is explored.Comment: 40 pages, 20 figures, 1 tabl

Perturbative QCD Calculations of Elliptic Flow and Shear Viscosity in Au+Au Collisions at sNN=200\sqrt{s_{NN}}=200 GeV

The elliptic flow $v_2$ and the ratio of the shear viscosity over the entropy density, $\eta/s$, of gluon matter are calculated from the perturbative QCD (pQCD) based parton cascade Boltzmann approach of multiparton scatterings. For Au+Au collisions at $\sqrt{s}=200$A GeV the gluon plasma generates large $v_2$ values measured at the BNL Relativistic Heavy Ion Collider. Standard pQCD yields $\eta/s\approx 0.08-0.15$ as small as the lower bound found from the anti-de Sitter/conformal field theory conjecture.Comment: 4 pages, 6 figures, new results added in Figs 1, 2, and 3, version published in PR