Hadronic and electromagnetic probes of hot and dense nuclear matter

Transport-theoretical Description of Nuclear Reactions

Kaon production in heavy ion reactions at intermediate energies

▪ Abstract We provide an overview of collective flow phenomena observed in heavy ion collisions from the Fermi energy range up to CERN Super Proton Synchrotron (SPS) energies. We summarize the experimental data in terms of the various observed aspects of flow, namely directed flow in the reaction plane, elliptic flow in- and out-of-plane, and azimuthally symmetric radial flow originating from the expansion of the hot and compressed reaction zone. Also reviewed are the theoretical concepts developed to simulate the complex reactions with the aim of extracting fundamental properties of hot and compressed nuclear matter.

Collective flow in heavy-ion collisions

The time-dependent variational principle for many-body trial states is used to discuss the relation between the approaches of different molecular-dynamics models that describe indistinguishable fermions. Early attempts to include effects of the Pauli principle by means of nonlocal potentials, as well as more recent models that work with antisymmetrized many-body states, are reviewed under these premises.

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Molecular dynamics for fermions

The role of the Δ (1920) resonance for kaon production in heavy ion collisions

In-medium effects in the description of heavy-ion collisions with realistic NN interactions

Temperature-dependent mean field and its effect on heavy-ion reactions

The long mean free path of $K^+$ mesons in nuclear matter makes this particle a suitable messenger for the dynamics of nucleus-nucleus reactions at intermediate energies (100 MeV to 3 GeV per nucleon). A prerequisite for this is the knowledge of the elementary production cross sections $\pi N \rightarrow \Sigma K$. Here these cross sections are studied for the first time with the explicite inclusion of the relevant baryon resonances up to 2 GeV as intermediate states. The baryon resonances -- $N(1710)\, I(J^P) = \frac{1}{2} (\frac{1}{2}^+),\, N(1720)\, \frac{1}{2} (\frac{3}{2}^+)$ and $\Delta(1920)\, \frac{3}{2} (\frac{3}{2}^+)\,$ -- are taken into account coherently in the calculations of the $\pi N \rightarrow \Sigma K$ process. (We refer to this model as the `resonance model'.) Also $K^*(892)\frac{1}{2} (1^-)$ vector meson exchange is included. It is shown that the total cross sections for different channels of the $\pi N \rightarrow \Sigma k$ reactions, i.e. $\pi^+ p \rightarrow \Sigma^+ K^+$, $\pi^- p \rightarrow \Sigma^- K^+$, $\pi^+ n \rightarrow \Sigma^0 K^+$ ($\pi^- p \rightarrow \Sigma^- K^+$) and $\pi^0 p \rightarrow \Sigma^0 K^+$ differ not only by absolute values but also by their energy dependence. This shape differences are due to the mixture of the isospin $I = 3/2$ $\Delta(1920)$ with isospin $I = 1/2$ nucleon resonances. However, this $I = 3/2$ resonance does not give a contribution to the $\pi N \rightarrow \Lambda K$ reactions. So the shapes of the total cross sections $\pi N \rightarrow \Lambda K$ for different isospin projections are the same. In spite of this, such cross sections averaged over different isospin projections in the same multiplet

The Role of the $\Delta(1920)$ Resonance for Kaon Production in Heavy Ion Collisions

Heavy-ion collisions at intermediate energies are studied by using a new relativistic quantum molecular dynamics (RQMD) code, which is a covariant generalization of the quantum molecular dynamics (QMD) approach. We show that this new implementation is able to produce the same results in the nonrelativistic limit (i.e., 50 MeV/nucleon) as the noncovariant QMD. Such a comparison is not available in the literature. At higher energies (i.e., 1.5 GeV/nucleon and 2 GeV/nucleon) RQMD and QMD give different results in respect to the time evolution of the phase space, for example for the directed transverse flow. These differences show that consequences of a covarient description of heavy-ion reactions within the framework of RQMD exist even at intermediate energies.

S.W. Huang

Papers

The role of the Δ (1920) resonance for kaon production in heavy ion collisions

In-medium effects in the description of heavy-ion collisions with realistic NN interactions

Temperature-dependent mean field and its effect on heavy-ion reactions

The Role of the $\Delta(1920)$ Resonance for Kaon Production in Heavy Ion Collisions

Consequences of a covariant description of heavy-ion reactions at intermediate energies