1,740 research outputs found
Particle abundances and spectra in the hydrodynamical description of relativistic nuclear collisions with light projectiles
We show that a hydrodynamical model with continuous particle emission instead
of sudden freeze out may explain both the observed strange particle and pion
abundances and transverse mass spectra for light projectile at SPS energy. We
found that the observed enhancement of pion production corresponds, within the
context of continuous emission, to the maximal entropy production.Comment: 11 pages, 2 figure
Hadronic centrality dependence in nuclear collisions
The kaon number density in nucleus+nucleus and p+p reactions is investigated
for the first time as a function of the initial energy density and
is found to exhibit a discontinuity around =1.3 GeV/fm. This
suggests a higher degree of chemical equilibrium for
1.3 GeV/fm. It can also be interpreted as reflection of the same
discontinuity, appearing in the chemical freeze out temperature (T) as a
function of . The dependence of (u,d,s) hadrons,
whith N the number of participating nucleons, also indicates a high degree of
chemical equilibrium and T saturation, reached at 1.3 GeV/fm.
Assuming that the intermediate mass region (IMR) dimuon enhancement seen by
NA50 is due to open charm (), the following observation can be made:
a) Charm is not equilibrated. b) suppression -unlike
- appears also in S+A collisions, above 1
GeV/fm. c) Both charm and strangeness show a discontinuity near the same
. d) could be formed mainly through coalescence.
e) The enhancement factors of hadrons with u,d,s,c quarks may be connected in a
simple way to the mass gain of these particles if they are produced out of a
quark gluon plasma (QGP). We discuss these results as possible evidence for the
QCD phase transition occuring near 1.3 GeV/fm.Comment: 4 pages, 4 figures, proceedings of Vth International Conference on
Strangeness in Quark Matter, 20-25 July 2000, Berkeley, California. To appear
in Journal of Physics G: Nuclear and Particle Physic
Local orientational order in the Stockmayer liquid
Phase behaviour of the Stockmayer fluid is studied with a method similar to
the Monte-Carlo annealing scheme. We introduce a novel order parameter which is
sensitive to the local co-orientation of the dipoles of particles in the fluid.
We exhibit a phase diagram based on the behaviour of the order parameter in the
density region 0.1 \leq {\rho}\ast \leq 0.32. Specifically, we observe and
analyse a second order locally disordered fluid \rightarrow locally oriented
fluid phase transition.Comment: 13 pages, 7 figure
Formation of Centauro and Strangelets in Nucleus-Nucleus Collisions at the LHC and their Identification by the ALICE Experiment
We present a phenomenological model which describes the formation of a
Centauro fireball in nucleus-nucleus interactions in the upper atmosphere and
at the LHC, and its decay to non-strange baryons and Strangelets. We describe
the CASTOR detector for the ALICE experiment at the LHC. CASTOR will probe, in
an event-by-event mode, the very forward, baryon-rich phase space 5.6 < \eta <
7.2 in 5.5 A TeV central Pb + Pb collisions. We present results of simulations
for the response of the CASTOR calorimeter, and in particular to the traversal
of Strangelets.Comment: 4 pages, 4 figures, to appear in the proceedings of the 26th ICR
CASTOR: Centauro and Strange Object Research in nucleus-nucleus collisions at LHC
We describe the CASTOR detector designed to probe the very forward,
baryon-rich rapidity region in nucleus-nucleus collisions at the LHC. We
present a phenomenological model describing the formation of a QGP fireball in
a high baryochemical potential environment, and its subsequent decay into
baryons and strangelets. The model explains Centauros and the long-penetrating
component and makes predictions for the LHC.
Simulations of Centauro-type events were done. To study the response of the
apparatus to new effects different exotic species (DCC, Centauros, strangelets
etc.) were passed through the deep calorimeter. The energy deposition pattern
in the calorimeter appears to be a new clear signature of the QGP.Comment: Talk given by E. Gladysz-Dziadus for the CASTOR group, Intern.
Workshop on Nuclear Theory, 10-15 June, 2002, Bulgaria, Rila Mountains, 15
pages, 14 figure
Confronting particle emission scenarios with strangeness data
We show that a hadron gas model with continuous particle emission instead of
freeze out may solve some of the problems (high values of the freeze out
density and specific net charge) that one encounters in the latter case when
studying strange particle ratios such as those by WA85. This underlines the
necessity to understand better particle emission in hydrodynamics to be able to
analyze data. It also re-opens the possibility of a quark-hadron transition
occuring with phase equilibrium instead of explosively.Comment: 13 pages, 2 figures, to appear in Phys. Rev. Let
Momentum Spectra of Charged Pions Produced in Proton-Proton Interactions Between 13 and 28.5 GeV/ c
Hydrodynamical assessment of 200 AGeV collisions
We are analyzing the hydrodynamics of 200 A GeV S+S collisions using a new
approach which tries to quantify the uncertainties arising from the specific
implementation of the hydrodynamical model. Based on a previous
phenomenological analysis we use the global hydrodynamics model to show that
the amount of initial flow, or initial energy density, cannot be determined
from the hadronic momentum spectra. We additionally find that almost always a
sizeable transverse flow deve- lops, which causes the system to freeze out,
thereby limiting the flow velocity in itself. This freeze-out dominance in turn
makes a distinction between a plasma and a hadron resonance gas equation of
state very difficult, whereas a pure pion gas can easily be ruled out from
present data. To complete the picture we also analyze particle multiplicity
data, which suggest that chemical equilibrium is not reached with respect to
the strange particles. However, the over- population of pions seems to be at
most moderate, with a pion chemical potential far away from the Bose
divergence.Comment: 19 pages, 11 figs in separate uuencoded file, for LateX, epsf.tex,
dvips, TPR-94-5 and BNL-(no number yet
Systematic Study of the Kaon to Pion Multiplicity Ratios in Heavy-Ion Collisions
We present a systematic study of the kaon to pion multiplicity ratios (K+/pi+
and K-/pi-) in heavy-ion collisions from AGS to RHIC energy using the
Relativistic Quantum Molecular Dynamics (RQMD) model. The model satisfactorily
describes the available experimental data on K+/pi+ and K-/pi-. Within the
model, we find that the strong increase of the ratios with the number of
participants is mainly due to hadronic rescattering of produced mesons with
ingoing baryons and their resonances. The enhancement of K/pi in heavy-ion
collisions with respect to elementary p+p interactions is larger at AGS energy
than SPS energy, and decreases smoothly with bombarding energy. The total
multiplicity ratios at RHIC energy are predicted by RQMD to be K+/pi+ = 0.19
and K-/pi- = 0.15.Comment: 10 pages, 8 figures, RevTeX style. A section is added to discuss
effects of rope formatio
Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions () and electrons (e). Using these moments the excitation function of
the fluctuation measure [A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
agrees with previously published NA49 results on the related
measure . Moreover, was found to depend
on the phase space coverage for [K,p] and [K,] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
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