229 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.
Kaon production at subthreshold and threshold energies
We summarize what we have learnt about the kaon production in nucleus-nucleus
collisions in the last decade. We will address three questions: a) Is the
production sensitive to the nuclear equation of state? b) How can it happen
that at the same excess energy the same number of and are produced
in heavy ion collisions although the elementary cross section in pp collisions
differs by orders of magnitudes? and c) Why kaons don't flow?Comment: 5 pages, 4 figures, contribution to Strange Quark Matter 200
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.
Modelling the many-body dynamics of heavy ion collisions: Present status and future perspective
Basic problems of the semiclassical microscopic modelling of strongly
interactingsystems are discussed within the framework of Quantum Molecular
Dynamics (QMD). This model allows to study the influence of several types of
nucleonic interactions on a large variety of observables and phenomena
occurring in heavy ion collisions at relativistic energies.It is shown that the
same predictions can be obtained with several -- numerically completely
different and independently written -- programs as far as the same model
parameters are employed and the same basic approximations are made. Many
observables are robust against variations of the details of the model
assumptions used. Some of the physical results, however, depend also on rather
technical parameters like the preparation of the initial configuration in phase
space. This crucial problem is connected with the description of the ground
state of single nuclei,which differs among the various approaches. An outlook
to an improved molecular dynamics scheme for heavy ion collisions is given.Comment: 39 pages, 12 figure
Analysis of kaon spectra at SIS energies - what remains from the KN potential
We study the reaction Au+Au at 1.48 AGeV and analyze the influence of the KN
optical potential on cm spectra and azimuthal distributions at mid-rapidity. We
find a significant change of the yields but only slight changes in the shapes
of the distributions when turning off the optical potential. However, the
spectra show contributions from different reaction times, where early kaons
contribute stronger to higher momenta and late kaons to lower momenta.
Azimuthal distributions of the kaons at mid-rapidity show a strong centrality
dependence. Their shape is influenced by the KN optical potential as well as by
re-scattering.Comment: SQM 2003 proceedings, 4 figures, 6 page
On the elliptical flow in asymmetric collisions and nuclear equation of state
We here present the results of elliptical flow for the collision of different
asymmetric nuclei (10Ne20 +13 Al27, 18Ar40 +21 Sc45, 30Zn64 +28 Ni58, 36Kr86
+41 Nb93) by using the Quantum Molecular Dynamics (QMD) model. General features
of elliptical flow are investigated with the help of theoretical simulations.
The simulations are performed at different beam energies between 40 and 105
MeV/nucleon. A significant change can be seen from in-plane to out-of-plane
elliptical flow of different fragments with incident energy. A comparison with
experimental data is also made. Further, we predict, for the first time that,
elliptical flow for different kind of fragments follow power law dependence ?
C(Atot)? for asymmetric systems
Influence of the pion-nucleon interaction on the collective pion flow in heavy ion reactions
We investigate the influence of the real part of the in-medium pion optical
potential on the pion dynamics in intermediate energy heavy ion reactions at 1
GeV/A. For different models, i.e. a phenomenological model and the
--hole model, a pionic potential is extracted from the dispersion
relation and used in Quantum Molecular Dynamics calculations. In addition with
the inelastic scattering processes we thus take care of both, real and
imaginary part of the pion optical potential. A strong influence of the real
pionic potential on the pion in-plane flow is observed. In general such a
potential has the tendency to reduce the anticorrelation of pion and nucleon
flow in non-central collisions.Comment: 12 pages Latex, 4 PS-figure
An Improved Quantum Molecular Dynamics Model and its Applications to Fusion Reaction near Barrier
An improved Quantum Molecular Dynamics model is proposed. By using this
model, the properties of ground state of nuclei from Li to Pb can
be described very well with one set of parameters. The fusion reactions for
Ca+Zr, Ca+Zr and Ca+Zr at energy near
barrier are studied by this model. The experimental data of the fusion cross
sections for Ca+Zr at the energy near barrier can be
reproduced remarkably well without introducing any new parameters. The
mechanism for the enhancement of fusion probability for fusion reactions with
neutron-rich projectile or target is analyzed.Comment: 20 pages, 12 figures, 3 table
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