137 research outputs found
Emissivity and conductivity of parton-hadron matter
We investigate the properties of the QCD matter across the deconfinement
phase transition. In the scope of the parton-hadron string dynamics (PHSD)
transport approach, we study the strongly interacting matter in equilibrium as
well as the out-of equilibrium dynamics of relativistic heavy-ion collisions.
We present here in particular the results on the electromagnetic radiation,
i.e. photon and dilepton production, in relativistic heavy-ion collisions and
the relevant correlator in equilibrium, i.e. the electric conductivity. By
comparing our calculations for the heavy-ion collisions to the available data,
we determine the relative importance of the various production sources and
address the possible origin of the observed strong elliptic flow of
direct photons.Comment: 4 pages, talk at the International Nuclear Physics Conference (INPC
2013), published versio
Dynamical equilibration of strongly interacting "infinite" parton matter within the parton-hadron-string dynamics transport approach
We study the kinetic and chemical equilibration in "infinite" parton matter
within the parton-hadron-string dynamics off-shell transport approach, which is
based on a dynamical quasiparticle model (DQPM) for partons matched to
reproduce lattice QCD results-including the partonic equation of state-in
thermodynamic equilibrium. The "infinite" parton matter is simulated by a
system of quarks and gluons within a cubic box with periodic boundary
conditions, at different energy densities, initialized slightly out of kinetic
and chemical equilibrium. We investigate the approach of the system to
equilibrium and the time scales for the equilibration of different observables.
We, furthermore, study particle distributions in the strongly interacting
quark-gluon plasma (sQGP) including partonic spectral functions, momentum
distributions, abundances of the different parton species and their
fluctuations (scaled variance, skewness, and kurtosis) in equilibrium. We also
compare the results of the microscopic calculations with the ansatz of the
DQPM. It is found that the results of the transport calculations are in
equilibrium well matched by the DQPM for quarks and antiquarks, while the gluon
spectral function shows a slightly different shape due to the explicit
interaction of partons. The time scales for the relaxation of fluctuation
observables are found to be shorter than those for the average values.
Furthermore, in the local subsystem, a strong change of the fluctuation
observables with the size of the local volume is observed. These fluctuations
no longer correspond to those of the full system and are reduced to Poissonian
distributions when the volume of the local subsystem becomes much smaller than
the total volume.Comment: 21 pages, 20 figure
Dilepton production in nucleus-nucleus collisions at top SPS energy within the Parton-Hadron-String Dynamics (PHSD) transport approach
Dilepton production in In+In collisions at 158 AGeV is studied within the
microscopic parton-hadron-string dynamics (PHSD) transport approach that
incorporates explicit partonic degrees-of-freedom, dynamical hadronization as
well as the more familiar hadronic dynamics in the final reaction stages. A
comparison to the data of the NA60 Collaboration shows that the measured
dilepton yield is well described by including the collisional broadening of
vector mesons, while simultaneously accounting for the electromagnetic
radiation of the strongly coupled quark-gluon plasma (sQGP) via off-shell
quark-antiquark annihilation, quark annihilation with additional gluon
Bremsstrahlung and the gluon-Compton scattering mechanisms. In particular, the
spectra in the intermediate mass range (1 GeV < M < 2.5 GeV) are dominated by
quark-antiquark annihilation in the nonperturbative QGP. Also, the observed
softening of the transverse mass spectra at intermediate masses (1 GeV < M <
2.5 GeV) is approximately reproduced. Furthermore, for dileptons of low masses
(M < 0.6 GeV), we find a sizable contribution from the quark annihilation with
additional gluon bremsstrahlung, thus providing another possible window for
probing the properties of the sQGP.Comment: 16 pages, 14 figure
- …