917 research outputs found

### Hydrodynamical analysis of flow at RHIC

We use a hydrodynamical model to describe the evolution of the collision
system at collision energies sqrt{s}=130 and 200 GeV. At lower sqrt{s}=130 GeV
energy we compare the results obtained assuming fast or slow thermalization
(thermalization times tau_0=0.6 and 4.1 fm/c, respectively) and show that slow
thermalization fails to reproduce the observed anisotropy of particle
distribution. At sqrt{s}=200 GeV collision energy our results show anisotropies
similar to those observed at sqrt{s}=130 GeV.Comment: 5 pages, INPC 2001 conference proceedings, uses the class "aipproc

### Anisotropy of flow and the order of phase transition in relativistic heavy ion collisions

Using a hydrodynamical model we study how the order of phase transition in
the equation of state of strongly interacting matter affects single particle
spectra, elliptic flow and higher order anisotropies in Au+Au collisions at
RHIC (sqrt{s_NN}=200 GeV energy). We find that the single particle spectra are
independent of the order of phase transition and that the fourth harmonic
v_4(p_T) shows only a weak dependence in the p_T region where hydrodynamics is
expected to work. The differential elliptic flow, v_2(p_T), of baryons shows
the strongest dependence on equation of state. Surprisingly the closest fit to
data was obtained when the equation of state had a strong first order phase
transition and a lattice inspired equation of state fits the data as badly as a
purely hadronic equation of state.Comment: A version to appear in Nuclear Physics A, a figure added where EoS is
compared with actual lattice results, minor changes in discussion, 21 pages,
10 figure

### Hadron Resonance Gas with Repulsive Interactions and Fluctuations of Conserved Charges

We discuss the role of repulsive baryon-baryon interactions in a hadron gas
using relativistic virial expansion and repulsive mean field approaches. The
fluctuations of the baryon number as well as strangeness-baryon correlations
are calculated in the hadron resonance gas with repulsive interactions and
compared with the recent lattice QCD results. In particular, we calculate the
difference between the second and fourth order fluctuations and correlations of
baryon number and strangeness, that have been proposed as probes of
deconfinement. We show that for not too high temperatures these differences
could be understood in terms of repulsive interactions.Comment: 12pages, 2 figures, ReVTeX, published version, unexpanded mean field
results adde

### Baryonic contributions to e+e- yields in a hydrodynamic model of Pb+Au collisions at the SPS

We analyze e+e- yields from matter containing baryons in addition to mesons
using a hydrodynamic approach to describe Pb+Au collisions at 158 A GeV/c. We
use two distinctly different e+e- production rates to provide contrast.
Although the presence of baryons leads to significant enhancement of e+e-
emission relative to that from mesons-only matter, the calculated results fall
below the data in the range 400 < M/MeV < 600. The calculated results are,
however, only 1.3-1.5 standard deviations below the data, which may not be
statistically significant.Comment: 4 pages, 4 figures, proceedings of Quark Matter 9

### Dileptons from transport and hydrodynamical models

Transport and hydrodynamical models used to describe the expansion stage of a
heavy-ion collision at the CERN SPS give different dilepton spectrum even if
they are tuned to reproduce the observed hadron spectra. To understand the
origin of this difference we compare the dilepton emission from transport and
hydrodynamical models using similar initial states in both models. We find that
the requirement of pion number conservation in a hydrodynamical model does not
change the dilepton emission. Also the mass distribution from the transport
model indicates faster cooling and longer lifetime of the fireball.Comment: 5 pages, 2 Postscript figures, contribution to the `International
Workshop XXVIII on Gross Properties of Nuclei and Nuclear Excitations',
Hirschegg, Austria, January 16-22 200

### Equation of state at finite baryon density based on lattice QCD

We employ the lattice QCD data on Taylor expansion coefficients to extend our
previous parametrization of the equation of state to finite baryon density.
When we take into account lattice spacing and quark mass dependence of the
hadron masses, the Taylor coefficients at low temperature are equal to those of
hadron resonance gas. Thus the equation of state is smoothly connected to the
hadron resonance gas equation of state at low temperatures. We also show how
the elliptic flow is affected by this equation of state at the maximum SPS
energy.Comment: 4 pages, 4 figures, Paraller talk at Quark Matter 2011, 22-28 May
2011, Annecy, Franc

### Mass number scaling in ultra-relativistic nuclear collisions from a hydrodynamical approach

We study the different nucleus-nucleus collisions, O+Au, S+S, S+Ag, S+Au and
Pb+Pb, at the CERN-SPS energy in a one-fluid hydrodynamical approach using a
parametrization based on baryon stopping in terms of the thickness of colliding
nuclei. Good agreement with measured particle spectra is achieved. We deduce
the mass number scaling behaviour of the initial energy density. We find that
the equilibration time is nearly independent of the size of the colliding
nuclei.Comment: 27 pages, figures included, submitted to European Physical Journa

### Is there elliptic flow without transverse flow?

Azimuthal anisotropy of final particle distributions was originally
introduced as a signature of transverse collective flow. We show that finite
anisotropy in momentum space can result solely from the shape of the particle
emitting source. However, by comparing the differential anisotropy to recent
data from STAR collaboration we can exclude such a scenario, but instead show
that the data favour strong flow as resulting from a hydrodynamical evolution.Comment: To appear in proceedings of Quark Matter 2001, 4 pages LaTeX, uses
espcrc1.st

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