535 research outputs found
Azimuthal correlations of pions in relativistic heavy ion collisions at 1 GeV/nucl.
Triple differential cross sections of pions in heavy ion collisions at 1
GeV/nucl. are studied with the IQMD model. After discussing general properties
of resonance and pion production we focus on azimuthal correlations:
At projectile- and target-rapidities we observe an anticorrelation in the
in-plane transverse momentum between pions and protons. At c.m.-rapidity,
however, we find that high pions are being preferentially emitted
perpendicular to the event-plane. We investigate the causes of those
correlations and their sensitivity on the density and momentum dependence of
the real and imaginary part of the nucleon and pion optical potential.Comment: 40 pages, 18 eps-figures, uses psfig.sty; complete postscript file
available at ftp://th.physik.uni-frankfurt.de/pub/bass/GSI-preprint_95-7.ps.
Collective flow of open and hidden charm in Au+Au collisions at = 200 GeV
We study the collective flow of open charm mesons and charmonia in Au+Au
collisions at = 200 GeV within the hadron-string-dynamics (HSD)
transport approach. The detailed studies show that the coupling of
mesons to the light hadrons leads to comparable directed and elliptic flow as
for the light mesons. This also holds approximately for mesons since
more than 50% of the final charmonia for central and mid-central collisions
stem from induced reactions in the transport calculations. The
transverse momentum spectra of mesons and 's are only very
moderately changed by the (pre-)hadronic interactions in HSD which can be
traced back to the collective flow generated by elastic interactions with the
light hadrons.Comment: 9 pages, 8 figures, Phys. Rev. C, in pres
J/psi Suppression and Enhancement in Au+Au Collisions at the BNL RHIC
We consider the production of the J/psi mesons in heavy ion collisions at
RHIC energies in the statistical coalescence model with an exact (canonical
ensemble) charm conservation. The c\bar{c} quark pairs are assumed to be
created in the primary hard parton collisions, but the formation of the open
and hidden charm particles takes place at the hadronization stage and follows
the prescription of statistical mechanics. The dependence of the J/psi
production on both the number of nucleon participants and the collision energy
is studied. The model predicts the J/psi suppression for low energies, whereas
at the highest RHIC energy the model reveals the J/psi enhancement.Comment: 14 pages, REVTeX, 3 PS-figure
Statistical Coalescence Model Analysis of J/psi Production in Pb+Pb Collisions at 158 A GeV
Production of J/\psi mesons in heavy ion collisions is considered within the
statistical coalescence model. The model is in agreement with the experimental
data of the NA50 Collaboration for Pb+Pb collisions at 158 A GeV in a wide
centrality range, including the so called ``anomalous'' suppression domain. The
model description of the J/psi data requires, however, strong enhancement of
the open charm production in central Pb+Pb collisions. This model prediction
may be checked in the future SPS runs.Comment: 13 pages, REVTeX, 2 PS-figure
Charm coalescence at relativistic energies
The J/psi yield at midrapidity at the top RHIC (relativistic heavy ion
collider) energy is calculated within the statistical coalescence model, which
assumes charmonium formation at the late stage of the reaction from the charm
quarks and antiquarks created earlier in hard parton collisions. The results
are compared to the new PHENIX data and to predictions of the standard models,
which assume formation of charmonia exclusively at the initial stage of the
reaction and their subsequent suppression. Two versions of the suppression
scenario are considered. One of them assumes gradual charmonium suppression by
comovers, while the other one supposes that the suppression sets in abruptly
due to quark-gluon plasma formation. Surprisingly, both versions give very
similar results. In contrast, the statistical coalescence model predicts a few
times larger yield in the most central collisions.Comment: 5 pages, RevTeX4, 1 PS-figure. V2: The final PHENIX data are analyze
Charmonium chemistry in A+A collisions at relativistic energies
Charmonium production and suppression in heavy-ion collisions at relativistic
energies is investigated within different models, i.e. the comover absorption
model, the threshold suppression model, the statistical coalescence model and
the HSD transport approach. In HSD the charmonium dissociation cross sections
with mesons are described by a simple phase-space parametrization including an
effective coupling strength for the charmonium states . This allows to include the backward channels for
charmonium reproduction by channels -- which are missed in the
comover absorption and threshold suppression model -- employing detailed
balance without introducing any new parameters. It is found that all approaches
yield a reasonable description of suppression in S+U and Pb+Pb
collisions at SPS energies. However, they differ significantly in the
ratio versus centrality at SPS and especially at RHIC
energies. These pronounced differences can be exploited in future measurements
at RHIC to distinguish the hadronic rescattering scenarios from quark
coalescence close to the QGP phase boundary.Comment: 13 pages, 8 figures, to be published in Phys. Rev.
On the Observation of Phase Transitions in Collisions of Elementary Matter
We investigate the excitation function of directed flow, which can provide a
clear signature of the creation of the QGP and demonstrate that the minimum of
the directed flow does not correspond to the softest point of the EoS for
isentropic expansion. A novel technique measuring the compactness is introduced
to determine the QGP transition in relativistic-heavy ion collisions: The QGP
transition will lead to higher compression and therefore to higher compactness
of the source in coordinate space. This effect can be observed by pion
interferometry. We propose to measure the compactness of the source in the
appropriate principal axis frame of the compactness tensor in coordinate space.Comment: LaTeX, 8 pages, 6 figures, Conference proceedings to CRIS 2000, 3rd
Catania Relativistic Ion Studie
The Disappearance of Flow
We investigate the disappearance of collective flow in the reaction plane in
heavy-ion collisions within a microscopic model (QMD). A systematic study of
the impact parameter dependence is performed for the system Ca+Ca. The balance
energy strongly increases with impact parameter. Momentum dependent
interactions reduce the balance energies for intermediate impact parameters
fm. Dynamical negative flow is not visible in the laboratory
frame but does exist in the contact frame for the heavy system Au+Au. For
semi-peripheral collisions of Ca+Ca with fm a new two-component
flow is discussed. Azimuthal distributions exhibit strong collectiv flow
signals, even at the balance energy.Comment: 19 pages, 7 eps-figures, uses psfig.sty; complete postscript file
available at
ftp://th.physik.uni-frankfurt.de/pub/bass/GSI-preprint_95-11.ps.
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