27 research outputs found
Non-equilibrated post freeze out distributions
We discuss freeze out on the hypersurface with time-like normal vector,
trying to answer how realistic is to assume thermal post freeze out
distributions for measured hadrons. Using simple kinetic models for gradual
freeze out we are able to generate thermal post FO distribution, but only in
highly simplified situation. In a more advanced model, taking into account
rescattering and re-thermalization, the post FO distribution gets more
complicated. The resulting particle distributions are in qualitative agreement
with the experimentally measured pion spectra. Our study also shows that the
obtained post FO distribution functions, although analytically very different
from the Juttner distribution, do look pretty much like thermal distributions
in some range of parameters.Comment: 14 pages, 2 figures, EPJ style, submitted to EPJ
Freeze-out in hydrodynamical models in relativistic heavy ion collisions
Freeze-out of particles across 3-dimensional space-time hypersurface with
space-like normal is discussed in a simple kinetic model. The final momentum
distribution of emitted particles shows a non-exponential transverse momentum
spectrum, which is in quantitative agreement with recently measured SPS pion
and spectra.Comment: 4 pages, 1 figure. Quark Matter'99 Proceeding
The 3rd Flow Component as a QGP Signal
Earlier fluid dynamical calculations with QGP show a softening of the
directed flow while with hadronic matter this effect is absent. On the other
hand, we indicated that a third flow component shows up in the reaction plane
as an enhanced emission, which is orthogonal to the directed flow. This is not
shadowed by the deflected projectile and target, and shows up at measurable
rapidities, . To study the formation of this effect initial stages
of relativistic heavy ion collisions are studied. An effective string rope
model is presented for heavy ion collisions at RHIC energies. Our model takes
into account baryon recoil for both target and projectile, arising from the
acceleration of partons in an effective field. The typical field strength
(string tension) for RHIC energies is about 5-12 GeV/fm, what allows us to talk
about "string ropes". The results show that QGP forms a tilted disk, such that
the direction of the largest pressure gradient stays in the reaction plane, but
deviates from both the beam and the usual transverse flow directions. The
produced initial state can be used as an initial condition for further
hydrodynamical calculations. Such initial conditions lead to the creation of
third flow component. Recent measurements are promising that this effect
can be used as a diagnostic tool of the QGP
The initial state of ultra-relativistic heavy ion collision
A model for energy, pressure and flow velocity distributions at the beginning
of ultra-relativistic heavy ion collisions is presented, which can be used as
an initial condition for hydrodynamic calculations. Our model takes into
account baryon recoil for both target and projectile, arising from the
acceleration of partons in an effective field, produced in the collision. The
typical field strength (string tension) for RHIC energies is about 5-12 GeV/fm,
what allows us to talk about "string ropes". The results show that a QGP forms
a tilted disk, such that the direction of the largest pressure gradient stays
in the reaction plane, but deviates from both the beam and the usual transverse
flow directions. Such initial conditions may lead to the creation of "antiflow"
or "third flow component".Comment: 28 pages, 9 figures. The presentation has been changed considerably.
Some parts of the model have been reformulated, what led to modifications in
several equations: (20-38), Apps. A, B. All the figures have been changed
from 100 GeV/nucl initial energy to the achieved RHIC energy of 65 GeV/nucl.
The last subplots in the Figs. 3, 4, 5, 6 present E=T^{00} in the laboratory
frame now, instead of the energy density in the local rest frame, e, shown in
the initial version. We also added the App. C to clarify the transformation
from space-time to lightcone coordinates and bac
Large enhancement from freeze out
Freeze out of particles across three dimensional space-time hypersurface is
discussed in a simple kinetic model. The final momentum distribution of emitted
particles, for freeze out surfaces with space-like normal, shows a
non-exponential transverse momentum spectrum. The slope parameter of the
distribution increases with increasing , in agreement with recently
measured SPS pion and spectra.Comment: 8 pages, 1 figure. Accepted for publication in Physics Letters
Nonideal particle distributions from kinetic freeze-out models
In fluid dynamical models the freeze-out of particles across a three-dimensional space-time hypersurface is discussed. The calculation of final momentum distribution of emitted particles is described for freeze-out surfaces, with both spacelike and timelike normals, taking into account conservation laws across the freeze-out discontinuity
Statistical Hadronization of Supercooled Quark-Gluon Plasma
The fast simultaneous hadronization and chemical freeze out of supercooled
quark-gluon plasma, created in relativistic heavy ion collisions, leads to the
re-heating of the expanding matter and to the change in a collective flow
profile. We use the assumption of statistical nature of the hadronization
process, and study quantitatively the freeze out in the framework of
hydrodynamical Bjorken model with different quark-gluon plasma equations of
state.Comment: 7 pages, 3 figure
QGP flow fluctuations and the characteristics of higher moments
The dynamical development of expanding Quark-gluon Plasma (QGP) flow is
studied in a 3+1D fluid dynamical model with a globally symmetric, initial
condition. We minimize fluctuations arising from complex dynamical processes at
finite impact parameters and from fluctuating random initial conditions to have
a conservative fluid dynamical background estimate for the statistical
distributions of the thermodynamical parameters. We also avoid a phase
transition in the equation of state, and we let the matter supercool during the
expansion.
Then central Pb+Pb collisions at TeV are studied in an
almost perfect fluid dynamical model, with azimuthally symmetric initial state
generated in a dynamical flux-tube model. The general development of
thermodynamical extensives are also shown for lower energies.
We observe considerable deviations from a thermal equilibrium source as a
consequence of the fluid dynamical expansion arising from a least fluctuating
initial state