68 research outputs found
Dynamics of Production in Heavy Ion Collisions close to Threshold
In this article the production of at energies close to the threshold is
studied in detail. The production mechanisms, the influence of in-medium
effects, cross sections, the nuclear equation of state and the dynamics of the
nucleons on the kaon dynamics are discussed. A special regard will be taken on
the collision of Au+Au at 1.5 GeV, a reaction that has recently been analyzed
in detail by experiments performed by the KaoS and FOPI collaborations at the
SIS accelerator at GSI.Comment: extract from habilitation at Nantes university (France), 76 pages, 76
figures, ps-file about 6M
Landau-Vlasov model versus Vlasov-Uehling-Uhlenbeck-approach : different flow effects from the same theory?
Differences between the Nantes-Ganil-Grenoble (NGG) LV-model and the original VUU approach are analysed. It is found that the LV code tends to simulate - for small timesteps - a non-viscous testparticle fluid
Transition from binary processes to multifragmentation in quantum molecular dynamics for intermediate-energy heavy ion collisions
We study the transition from fusion-fission phenomena at about 20 MeV/nucleon multifragmentation at 100–200 MeV/nucleon in the reaction 16O+80Br employing the quantum molecular dynamics model. The time evolution of the density and mass distribution, the charged-particle multiplicity, and spectra as well as angular distributions of light particles are investigated. The results exhibit the transition of the disassembly mechanism, but no sharp change is found. The results are in good agreement with recently measured 4-Pi data
Out-of-plane pion emission in relativistic heavy ion collisions: Spectroscopy of Delta resonance matter
Azimuthal correlations of pions are studied with the quantum molecular dynamics model. Pions are preferentially emitted perpendicular to the reaction plane. Our analysis shows that this anisotropy is dominated by pion absorption on the spectator matter in the reaction plane. Pions emitted perpendicular to the reaction plane undergo less rescattering than those emitted in the reaction plane and might therefore be more sensitive to the early hot and dense reaction phase
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 pt 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
Production of hypertritons in heavy ion collisions around the threshold of strangeness production
We use the Isospin Quantum Molecular Dynamics approach supplemented with a
phase space coalescence to study the properties of the production of
hypertritons. We see strong influences of the hyperon rescattering on the
yields. The hypertritons show up to be quite aligned to the properties of
nuclear matter underlining the necessity of rescattering to transport the
hyperons to the spectator matter.Comment: 8 pages, proceedings of 14th International Conference on Nuclear
Reaction Mechanisms, Varenna (Italy), 201
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 role of quantum effects and nonequilibrium transport coefficients for relativistic heavy ion collisions
Stopping power and thermalization in relativistic heavy ion collisions is investigated employing the quantum molecular dynamics approach. For heavy systems stopping of the incoming nuclei is predicted, independent of the energy. The influence of the quantum effects and their increasing importance at low energies, is demonstrated by inspection of the mean free path of the nucleons and the n-n collision number. Classical models, which neglect these effects, overestimate the stopping and the thermalization as well as the collective flow and squeeze out. The sensitivity of the transverse and longitudinal momentum transfer to the in-medium cross section and to the pressure is investigated
Nuclear transport models can reproduce charged-particle-inclusive measurements but are not strongly constrained by them
Nuclear transport models are important tools for interpretation of many heavy-ion experiments and are essential in efforts to probe the nuclear equation of state. In order to fulfill these roles, the model predictions should at least agree with observed single-particle-inclusive momentum spectra; however, this agreement has recently been questioned. The present work compares the Vlasov-Uehling-Uhlenbeck model to data for mass-symmetric systems ranging from 12C+12C to 139La+139La, and we find good agreement within experimental uncertainties at 0.4A and 0.8A GeV. For currently available data, these uncertainties are too large to permit effective nucleon-nucleon scattering cross sections in the nuclear medium to be extracted at a useful level of precision
Neural networks for impact parameter determination
Accurate impact parameter determination in a heavy-ion collision is crucial for almost all further analysis. We investigate the capabilities of an artificial neural network in that respect. First results show that the neural network is capable of improving the accuracy of the impact parameter determination based on observables such as the flow angle, the average directed inplane transverse momentum and the difference between transverse and longitudinal momenta. However, further investigations are necessary to discover the full potential of the neural network approach
- …