56 research outputs found
On the Role of Dissipation in the Early Stages of Relativistic Heavy Ion Collisions
The influence of the dissipative terms on the conditions of formation and the
characteristic parameters of shock waves in relativistic nuclear collisions is
investigated for three types of equation of state (non linear QHD-1, resonance
gas and lattice QCD). Energy and velocity profiles are obtained in a
one-dimensional model; the duration of the shock phase and width of the shock
front are calculated. It is shown that the presence of a phase transition
results in a strong enhancement of the width of the shock front, which results
in an increase of transparency. This effect, combined with the fact that the
nuclei have a finite size, prevents the energy density to rise to its maximum
value (full stopping) as would be predicted by a non dissipative shock model.Comment: 30 pages, 18 figures, uuencoded compressed postscript file (with
figures already embedded), submitted to Nucl. Phys.
pi-/pi+ ratio in heavy ions collisions: Coulomb effect or chemical equilibration?
We calculate the pi-/pi+ ratio for Pb+Pb at CERN/SPS energies and for Au+Au
at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without
consideration of Coulomb effect an enhancement of this ratio at low mt is found
compatible with that observed in these experiments. Our calculations are based
on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which
described many other aspects of experimental data. In this model the observed
enhancement is a consequence of baryon and strangeness conservation and of
chemical equilibration of the system and is caused by the decay of produced
hyperons, which leads to a difference in the total number of positive and
negative pions as well. Based on the same approach, we also present results for
the pi-/pi+ ratio for S+S (CERN/SPS) collisions, where we find a similar
effect. The absence of the enhancement of the pi-/pi+ ratio in the S+S data
presented by the NA44 Collaboration, if confirmed, could indicate that chemical
equilibration has not yet been estabilished in this reaction.Comment: 8 pages and 2 figures, submmited to Phys. Lett. B. This reviewed
version (Nov.29,1996) contains more details about the model simulated
efficiency considering the experimental detection conditions. Other small
modifications were mad
Bose-condensation through resonance decay
We show that a system described by an equation of state which contains a high
number of degrees of freedom (resonances) can create a considerable amount of
superfluid (condensed) pions through the decay of short-lived resonances, if
baryon number and entropy are large and the dense matter decouples from
chemical equilibrium earlier than from thermal equilibrium. The system cools
down faster in the presence of a condensate, an effect that may partially
compensate the enhancement of the lifetime expected in the case of
quark-gluon-plasma formation.Comment: 12 pages GSI-93-27 PREPRIN
Hydrodynamical Beam Jets in High Energy Hadronic Collisions
A study of hadronic data up to TEVATRON energies in terms of relativistic
hydrodynamics indicates an extended 1-dimensional stage of the expansion which
suggests a jet like behaviour of the fireball along the collision axis.Comment: 3 pages (1 page of figures) ,(LATEX), GSI-93-2
Hydrodynamical analysis of single inclusive spectra and Bose-Einstein correlations for at 160 AGeV
We present the first analysis of preliminary data for at 160
using 3+1-dimensional relativistic hydrodynamics. We find excellent agreement
with the rapidity spectra of negative hadrons and the correlation measurements.
The data indicates a large amount of stopping; of the invariant energy
of the collision is thermalized and of the baryons are contained in the
central fireball. Within our model this implies that a quark-gluon-plasma of
lifetime 3.4 was formed.Comment: 13 pages, 5 Postscript figures (attached to this file as compressed
and uuencoded Postscript file
Probing the equation of state in the AGS energy range with 3-d hydrodynamics
The effect of (i) the phase transition between a quark gluon plasma (QGP) and
a hadron gas and (ii) the number of resonance degrees of freedom in the
hadronic phase on the single inclusive distributions of 16 different types of
produced hadrons for Au+Au collisions at AGS energies is studied.
We have used an exact numerical solution of the relativistic hydrodynamical
equations without free parameters which, because of its 3-d character,
constitutes a considerable improvement over the classical Landau solution.
Using two different equations of state (eos) - one containing a phase
transition from QGP to the Hadronic Phase and two versions of a purely hadronic
eos - we find that the first one gives an overall better description of the
Au+Au experimental data at energies.
We reproduce and analyse measured meson and proton spectra and also make
predictions for anti-protons, deltas, anti-deltas and hyperons. The low m_t
enhancement in pi- spectra is explained by baryon number conservation and
strangeness equilibration.
We also find that negative kaon data are more sensitive to the eos, as well
as the K-/pi- ratio. All hyperons and deltas are sensitive to the presence of a
phase transition in the forward rapidity region. Anti-protons, Omegas and heavy
anti-baryons are sensitive in the whole rapidity range.Comment: 25 pages (.tex) and 9 figures (.ps
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