92 research outputs found
Baryon Junction Stopping at the SPS and RHIC via HIJING/B
Baryon stopping at the SPS and RHIC energies is calculated by introducing a
new baryon junction mechanism into HIJING. The exchange of a baryon junction,
according to Regge phenomenology, leads to a cosh(y/2) rapidity dependence and
an s^(-1/4) energy dependence of the inclusive baryon cross section. This
baryon junction dynamics also leads naturally to enhanced p_T broadening in pA
and AA together with enhanced mid-rapidity hyperon production.Comment: Proceedings for Quark Matter 97; 4 pages, 1 eps-figur
Domain Wall Bubbles in High Energy Heavy Ion Collisions
It has been recently shown that meta-stable domain walls exist in
high-density QCD () as well as in QCD with large number of colors
(), with the lifetime being exponentially long in both cases.
Such metastable domain walls may exist in our world as well, especially in hot
hadronic matter with temperature close to critical. In this paper we discuss
what happens if a bubble made of such wall is created in heavy ion collisions,
in the mixed phase between QGP and hadronic matter. We show it will further be
expanded to larger volume by the pion pressure, before it
disappears, either by puncture or contraction. Both scenarios leave distinctive
experimental signatures of such events, negatively affecting the interference
correlations between the outgoing pions.Comment: 6 pages, 1 fi
A Study of Parton Energy Loss in Au+Au Collisions at RHIC using Transport Theory
Parton energy loss in Au+Au collisions at RHIC energies is studied by
numerically solving the relativistic Boltzmann equation for the partons
including and collision
processes. Final particle spectra are obtained using two hadronization models;
the Lund string fragmentation and independent fragmentation models. Recent,
preliminary transverse momentum distributions from central Au+Au
collisions at RHIC are reproduced using gluon-gluon scattering cross sections
of 5-12 mb, depending upon the hadronization model. Comparisons with the HIJING
jet quenching algorithm are made.Comment: 6 pages, 6 figures, attached files are replaced (wrong files were
uploaded in version 1
Baryon Number Fluctuation and the Quark-Gluon Plasma
We show that or , the squared baryon or
antibaryon number fluctuation per baryon or antibaryon, is a possible signature
for the quark-gluon plasma that is expected to be created in relativistic heavy
ion collisions, as it is a factor of three smaller than in an equilibrated
hadronic matter due to the fractional baryon number of quarks. Using kinetic
equations with exact baryon number conservation, we find that their values in
an equilibrated matter are half of those expected from a Poisson distribution.
Effects due to finite acceptance and non-zero net baryon number are also
studied.Comment: discussion and references added, version to appear in PR
A model for net-baryon rapidity distribution
In nuclear collisions, a sizable fraction of the available energy is carried
away by baryons. As the baryon number is conserved, the net-baryon
retains information on the energy-momentum carried by the incoming nuclei. A
simple and consistent model for net-baryon production in high energy
proton-proton and nucleus-nucleus collisions is presented. The basic
ingredients of the model are valence string formation based on standard PDFs
with QCD evolution and string fragmentation via the Schwinger mechanism. The
results of the model are presented and compared with data at different
centre-of-mass energies and centralities, as well as with existing models.
These results show that a good description of the main features of net-baryon
data is possible in the framework of a simplistic model, with the advantage of
making the fundamental production mechanisms manifest.Comment: 9 pages, 12 figures; in fig. 11 a) the vertical scale was correcte
Matter-Antimatter Asymmetry in the Large Hadron Collider
The matter-antimatter asymmetry is one of the greatest challenges in the
modern physics. The universe including this paper and even the reader
him(her)self seems to be built up of ordinary matter only. Theoretically, the
well-known Sakharov's conditions remain the solid framework explaining the
circumstances that matter became dominant against the antimatter while the
universe cools down and/or expands. On the other hand, the standard model for
elementary particles apparently prevents at least two conditions out of them.
In this work, we introduce a systematic study of the antiparticle-to-particle
ratios measured in various and collisions over the last three
decades. It is obvious that the available experimental facilities turn to be
able to perform nuclear collisions, in which the matter-antimatter asymmetry
raises from at AGS to at LHC. Assuming that the final
state of hadronization in the nuclear collisions takes place along the
freezeout line, which is defined by a constant entropy density, various
antiparticle-to-particle ratios are studied in framework of the hadron
resonance gas (HRG) model. Implementing modified phase space and distribution
function in the grand-canonical ensemble and taking into account the
experimental acceptance, the ratios of antiparticle-to-particle over the whole
range of center-of-mass-energies are very well reproduced by the HRG model.
Furthermore, the antiproton-to-proton ratios measured by ALICE in
collisions is also very well described by the HRG model. It is likely to
conclude that the LHC heavy-ion program will produce the same particle ratios
as the program implying the dynamics and evolution of the system would not
depend on the initial conditions. The ratios of bosons and baryons get very
close to unity indicating that the matter-antimatter asymmetry nearly vanishes
at LHC.Comment: 9 pages, 5 eps-figures, revtex4-styl
Jet Quenching and the p-bar >= pi- Anomaly at RHIC
PHENIX data on Au+Au at root(s)_= 130 AGeV suggest that p-bar yields may
exceed pi- at high p_T > 2 GeV/c. We propose that jet quenching in central
collisions suppresses the hard PQCD component of the spectra in central A+A
reactions, thereby exposing a novel component of baryon dynamics that we
attribute to (gluonic) baryon junctions. We predict that the observed p-bar >=
pi- and the p > pi+ anomaly at p_T ~ 2 GeV/c is limited to a finite p_T window
that decreases with increasing impact parameter.Comment: 5 pages, 4 figures, REVTeX, uses bbox.sty. Final version: references
and figures updated. Added discussion on the p/pi+ rati
Last Call for RHIC Predictions
This paper contains the individual contributions of all speakers of the
session on 'Last Call for RHIC Predictions' at Quark Matter 99, and a summary
by the convenor.Comment: 56 pages, psfig, epsf, epsfig, graphicx style files required,
Proceedings of the XIV Int. Conf. on Nucleus-Nucleus Collisions, Quark Matter
99, Torino, Italy, May 10 - 15, 1999. Typographical mistakes corrected and
figure numbers change
Effect of tensor couplings in a relativistic Hartree approach for finite nuclei
The relativistic Hartree approach describing the bound states of both
nucleons and anti-nucleons in finite nuclei has been extended to include tensor
couplings for the - and -meson. After readjusting the parameters
of the model to the properties of spherical nuclei, the effect of
tensor-coupling terms rises the spin-orbit force by a factor of 2, while a
large effective nucleon mass sustains. The overall
nucleon spectra of shell-model states are improved evidently. The predicted
anti-nucleon spectra in the vacuum are deepened about 20 -- 30 MeV.Comment: 31 pages, 4 postscript figures include
Space-time evolution and HBT analysis of relativistic heavy ion collisions in a chiral SU(3) x SU(3) model
The space-time dynamics and pion-HBT radii in central heavy ion-collisions at
CERN-SPS and BNL-RHIC are investigated within a hydrodynamic simulation. The
dependence of the dynamics and the HBT-parameters on the EoS is studied with
different parametrisations of a chiral SU(3) sigma-omega model. The
selfconsistent collective expansion includes the effects of effective hadron
masses, generated by the nonstrange and strange scalar condensates. Different
chiral EoS show different types of phase transitions and even a crossover. The
influence of the order of the phase transition and of the difference in the
latent heat on the space-time dynamics and pion-HBT radii is studied. A small
latent heat, i.e. a weak first-order chiral phase transition, or even a smooth
crossover leads to distinctly different HBT predictions than a strong first
order phase transition. A quantitative description of the data, both at SPS
energies as well as at RHIC energies, appears difficult to achieve within the
ideal hydrodynamical approach using the SU(3) chiral EoS. A strong first-order
quasi-adiabatic chiral phase transition seems to be disfavored by the pion-HBT
data from CERN-SPS and BNL-RHIC
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