882 research outputs found
Mean Field Effects In The Quark-Gluon Plasma
A transport model based on the mean free path approach for an interacting
meson system at finite temperatures is discussed. A transition to a quark gluon
plasma is included within the framework of the MIT bag model. The results
obtained compare very well with Lattice QCD calculations when we include a mean
field in the QGP phase due to the Debye color screening. In particular the
cross over to the QGP at about 175 MeV temperature is nicely reproduced. We
also discuss a possible scenario for hadronization which is especially
important for temperatures below the QGP phase transition
Energy and centrality dependences of charged multiplicity density in relativistic nuclear collisions
Using a hadron and string cascade model, JPCIAE, the energy and centrality
dependences of charged particle pseudorapidity density in relativistic nuclear
collisions were studied. Within the framework of this model, both the
relativistic experimental data and the PHOBOS and PHENIX
data at =130 GeV could be reproduced fairly well without retuning
the model parameters. The predictions for full RHIC energy collisions
and for collisions at the ALICE energy were given. Participant nucleon
distributions were calculated based on different methods. It was found that the
number of participant nucleons, for distinguishing various theoretical models.Comment: 10 pages, 4 figures, submitted to Phy. Lett.
Transverse Energy Evolution as a Test of Parton Cascade Models
We propose a test of Monte Carlo Parton Cascade models based on analytic
solutions of covariant kinetic theory for longitudinally boost and transverse
translation invariant boundary conditions. We compute the evolution of the
transverse energy per unit rapidity for typical mini-jet initial conditions
expected in ultra-relativistic nuclear collisions. The kinetic theory solutions
under these conditions test the models severely because they deviate strongly
from free-streaming and also from ideal Euler and dissipative Navier-Stokes
hydrodynamical approximations. We show that the newly formulated ZPC model
passes this test. In addition, we show that the initial mini-jet density would
need to be approximately four times higher than estimated with the HIJING
generator in central Au+Au collisions at c.m. energies 200 AGeV in order that
parton cascade dynamics can be approximated by Navier-Stokes hydrodynamics.Comment: Latex 28 pages, including 5 figure (postscript embedded with psfig
The QGP phase in relativistic heavy-ion collisions
The dynamics of partons, hadrons and strings in relativistic nucleus-nucleus
collisions is analyzed within the novel Parton-Hadron-String Dynamics (PHSD)
transport approach, which is based on a dynamical quasiparticle model for
partons (DQPM) matched to reproduce recent lattice-QCD results - including the
partonic equation of state - in thermodynamic equilibrium. The transition from
partonic to hadronic degrees of freedom is described by covariant transition
rates for the fusion of quark-antiquark pairs or three quarks (antiquarks),
respectively, obeying flavor current-conservation, color neutrality as well as
energy-momentum conservation. The PHSD approach is applied to nucleus-nucleus
collisions from low SIS to RHIC energies. The traces of partonic interactions
are found in particular in the elliptic flow of hadrons as well as in their
transverse mass spectra.Comment: To be published by Springer in Proceedings of the International
Symposium on `Exciting Physics', Makutsi-Range, South Africa, 13-20 November,
201
Charged pions from Ni on Ni collisions between 1 and 2 AGeV
Charged pions from Ni + Ni reactions at 1.05, 1.45 and 1.93 AGeV are measured
with the FOPI detector. The mean multiplicities per mean number of
participants increase with beam energy, in accordance with earlier studies of
the Ar + KCl and La + La systems. The pion kinetic energy spectra have concave
shape and are fitted by the superposition of two Boltzmann distributions with
different temperatures. These apparent temperatures depend only weakly on
bombarding energy. The pion angular distributions show a forward/backward
enhancement at all energies, but not the enhancement which was
observed in case of the Au + Au system. These features also determine the
rapidity distributions which are therefore in disagreement with the hypothesis
of one thermal source. The importance of the Coulomb interaction and of the
pion rescattering by spectator matter in producing these phenomena is
discussed.Comment: 22 pages, Latex using documentstyle[12pt,a4,epsfig], to appear in Z.
Phys.
QGP Theory: Status and Perspectives
The current status of Quark-Gluon-Plasma Theory is reviewed. Special emphasis
is placed on QGP signatures, the interpretation of current data and what to
expect from RHIC in the near future.Comment: 20 pages, invited overview talk at the 4th International Conference
on the Physcis and Astrophysics of the Quark-Gluon-Plasma, November 2001,
Jaipur, India, to appear in Praman
absorption in hadronic matter
The cross sections of absorption by and mesons are
evaluated in a meson-exchange model. Including form factors with a cutoff
parameter of 1 or 2 GeV, we find that due to the large threshold of these
reactions the thermal average of their cross sections is only about 0.2 mb at a
temperature of 150 MeV. Our results thus suggest that the absorption of
directly produced by hadronic comovers in high energy heavy ion
collisions is unimportant.Comment: 11 pages, revtex, 3 figures, added references and discussion on
higher BBbar state
-scaling and Information Entropy in Ultra-Relativistic Nucleus-Nucleus Collisions
The -scaling method has been applied to ultra-relativistic p+p, C+C
and Pb+Pb collision data simulated using a high energy Monte Carlo package,
LUCIAE 3.0. The -scaling is found to be valid for some physical
variables, such as charged particle multiplicity, strange particle multiplicity
and number of binary nucleon-nucleon collisions from these simulated
nucleus-nucleus collisions over an extended energy ranging from = 20
to 200 A GeV. In addition we derived information entropy from the multiplicity
distribution as a function of beam energy for these collisions.Comment: 4 pages, 4 figures, 1 table; to appear in the July Issue of Chin.
Phys. Lett.. Web Page: http://www.iop.org/EJ/journal/CP
The Effect of Dynamical Parton Recombination on Event-by-Event Observables
Within a dynamical quark recombination model we explore various proposed
event-by-event observables sensitive to the microscopic structure of the
QCD-matter created at RHIC energies. Charge fluctuations, charge transfer
fluctuations and baryon-strangeness correlations are computed from a sample of
central Au+Au events at the highest RHIC energy available (=200
GeV). We find that for all explored observables, the calculations yield the
values predicted for a quark-gluon plasma only at early times of the evolution,
whereas the final state approaches the values expected for a hadronic gas. We
argue that the recombination-like hadronization process itself is responsible
for the disappearance of the predicted deconfinement signatures. This might
explain why no fluctuation signatures for the transition between quark and
hadronic matter was ever observed in the experimental data up to now. However,
it might also be interpreted as a clear indication for a recombination like
hadronization process at RHIC.Comment: 5 page
Study of relativistic nuclear collisions at AGS energies from p+Be to Au+Au with hadronic cascade model
A hadronic cascade model based on resonances and strings is used to study
mass dependence of relativistic nuclear collisions from p+Be to Au+Au at AGS
energies (\sim 10\AGeV) systematically. Hadron transverse momentum and
rapidity distributions obtained with both cascade calculations and Glauber type
calculations are compared with experimental data to perform detailed discussion
about the importance of rescattering among hadrons. We find good agreement with
the experimental data without any change of model parameters with the cascade
model. It is found that rescattering is of importance both for the explanation
of high transverse momentum tail and for the multiplicity of produced
particles.Comment: 27 pages, 30 figure
- …