Engineering topics

Cassing, W

Publications and source records attributed to Cassing, W.

6 records

DOE OSTI2012

Strongly interacting parton matter equilibration

We study the kinetic and chemical equilibration in 'infinite' parton matter within the Parton-Hadron-String Dynamics transport approach. The 'infinite' matter is simulated within a cubic box with periodic boundary conditions initialized at different energy densities. Particle abundances, kinetic energy distributions, and the detailed balance of the off-shell quarks and gluons in the strongly-interacting quarkgluon plasma are addressed and discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Dynamics of hot and dense nuclear and partonic matter

The dynamics of hot and dense nuclear matter is discussed from the microscopic transport point of view. The basic concepts of the Hadron-String-Dynamical transport model (HSD)-derived from Kadanoff-Baym equations in phase phase-are presented as well as 'highlights' of HSD results for different observables in heavy-ion collisions from 100 A MeV (SIS) to 21 A TeV(RHIC) energies. Furthermore, a novel extension of the HSD model for the description of the partonic phase-the Parton-Hadron-String-Dynamics (PHSD) approach-is introduced. PHSD includes a nontrivial partonic equation of state-in line with lattice QCD-as well as covariant transition rates from partonic to hadronic degrees of freedom. The sensitivity of hadronic observables to the partonic phase is demonstrated for relativistic heavy-ion collisions from the FAIR/NICA up to the RHIC energy regime.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2012

Fluctuations and correlations as a signal of deconfinement

Event-by-event fluctuations of the K/{pi}, K/p, and p/{pi} ratio in central AA collisions have been studied for SPS and RHIC energies. The Hadron-String-Dynamical transport approach (HSD) can qualitatively reproduce the measured excitation function for the K/{pi} ratio fluctuations. The di-jet azimuthal correlations also have been investigated within the HSD model. We found that the suppression of the away-side jet in the hadronic mediumis not enough to explain the experimental data from RHIC. The additional suppression should be attributed to a quark-gluon plasma produced in heavy-ion collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2011

Electromagnetic field evolution in relativistic heavy-ion collisions

The hadron string dynamics (HSD) model is generalized to include the creation and evolution of retarded electromagnetic fields as well as the influence of the magnetic and electric fields on the quasiparticle propagation. The time-space structure of the fields is analyzed in detail for noncentral Au + Au collisions at {radical}(s{sub NN})=200 GeV. It is shown that the created magnetic field is highly inhomogeneous, but in the central region of the overlapping nuclei it changes relatively weakly in the transverse direction. For the impact parameter b=10 fm, the maximal magnetic field - perpendicularly to the reaction plane - is obtained of order eB{sub y}/m{sub {pi}}{sup 2}{approx}5 for a very short time {approx}0.2 fm/c, which roughly corresponds to the time of a maximal overlap of the colliding nuclei. We find that at any time, the location of the maximum in the eB{sub y} distribution correlates with that of the energy density of the created particles. In contrast, the electric field distribution, being also highly inhomogeneous, has a minimum in the center of the overlap region. Furthermore, the field characteristics are presented as a function of the collision energy and the centrality of the collisions. To explore the effect of the back reaction of the fields on hadronic observables, a comparison of HSD results with and without fields is exemplified. Our actual calculations show no noticeable influence of the electromagnetic fields--created in heavy-ion collisions--on the effect of the electric charge separation with respect to the reaction plane.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2010

Jets propagation through a hadron-string medium

Di-jet correlations in nucleus-nucleus collisions are studied within the hadron-string-dynamics (HSD) transport approach taking into account the reaction of the medium on the jet energy loss nonperturbatively. A comparison with the STAR and PHENIX data in central Au+Au collisions at the Relativistic Heavy Ion Collider energy {radical}(s)=200 GeV is performed differentially (i.e., with respect to correlations in azimuthal angle {Delta}{phi} and pseudorapidity {Delta}{eta}). The HSD results do not show enough suppression for the 'away-side' jets in accordance with earlier perturbative studies. Furthermore, the 'Mach-cone' structure for the angle distribution in the away-side jet as well as 'ridge' long-range rapidity correlations in the 'near-side' jet - observed by the STAR, PHENIX, and PHOBOS Collaborations - are not seen in the HSD results, thus suggesting a partonic origin.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2010

Dilepton radiation by vector mesons and off-shell partons in the hot and dense medium

According to the dynamical quasiparticle model (DQPM) - matched to reproduce lattice QCD results in thermodynamic limit, - the constituents of the strongly interacting quark-gluon plasma (sQGP) are massive and off-shell quasi-particles (quarks and gluons) with broad spectral functions. In order to address the electromagnetic radiation of the sQGP, we derive off-shell cross sections of qq-bar{yields}{gamma}*, qq-bar{yields}{gamma}*+g and qg{yields}{gamma}*q(q-barg{yields}{gamma}*q-bar) reactions taking into account the effective propagators for quarks and gluons from the DQPM. Dilepton production in In+In collisions at 158 AGeV is studied by implementing these processes into the parton-hadron-string dynamics (PHSD) transport approach. The microscopic PHSD transport approach describes the full evolution of the heavy-ion collision: from the dynamics of quasi-particles in the sQGP phase (when the local energy density is above {approx}1 GeV/fm{sup 3}) through hadronization and to the following hadron interactions and off-shell propagation after the hadronization. A comparison to the data of the NA60 Collaboration shows that the low mass dilepton spectra are well described by including a collisional broadening of vector mesons, while the spectra in the intermediate mass range are dominated by off-shell quark-antiquark annihilation, quark Bremsstrahlung and gluon-Compton scattering in the nonperturbative QGP. In particular, the observed softening of the m{sub T} spectra at intermediate masses (1 GeV {<=} M {<=} 3 GeV) is approximately reproduced.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗