T. Gaitanos

Relativistic effects in the search for high density symmetry energy

Abstract Intermediate energy heavy ion collisions open the unique possibility to explore the equation of state (EOS) of nuclear matter far from saturation, in particular the density dependence of the symmetry energy. Within a relativistic transport model it is shown that the isovector–scalar δ meson, which affects the high density behavior of the symmetry energy density, influences the dynamics of heavy ion collisions in terms of isospin collective flows. The effect is largely enhanced by a relativistic mechanism related to the covariant nature of the fields contributing to the isovector channel. Results for reactions induced by 132 Sn radioactive beams are presented. The elliptic flows of nucleons and light isobars appear to be quite sensitive to microscopic structure of the symmetry term, in particular for particles with large transverse momenta, since they represent an earlier emission from a compressed source. Thus future, more exclusive, experiments with relativistic radioactive beams should be able to set stringent constraints on the density dependence of the symmetry energy far from ground state nuclear matter.

Formation of hypernuclei in high energy reactions within a covariant transport model

Abstract We investigate the formation of fragments with strangeness degrees of freedom in proton- and heavy-ion-induced reactions at high relativistic energies. The model used is a combination of a dynamical transport model and a statistical approach of fragment formation. We discuss in detail the applicability and limitations of such a hybrid model by comparing data on spectator fragmentation at relativistic SIS / GSI -energies. The theoretical results are analyzed in terms of spectator fragmentation with strangeness degrees of freedom such as the production of single- Λ – He 3 , 4 , 5 hypernuclei. We provide theoretical estimates on the spectra and on inclusive cross sections of light hypernuclei, which could be helpful for future experiments on hypernuclear physics at the new GSI- and J-PARC-facilities.

Nuclear stopping and flow in heavy-ion collisions and the in-medium NN cross section

Abstract We present transport calculations for heavy-ion reactions in which the mean field and the in-medium nucleon–nucleon cross section are consistently based on the same effective interaction, i.e., the in-medium T-matrix from microscopic Dirac–Brueckner calculations. Doing so, the stopping in central reactions in terms of the recently proposed var tl observable and the correlation to the behavior of the directed flow is investigated. The relation to the nuclear shear viscosity is discussed.

Fragment formation in proton induced reactions within a BUU transport model

The formation of fragments in proton-induced reactions at low relativistic energies within a combination of a covariant dynamical transport model and a statistical approach is investigated. In particular, we discuss in detail the applicability and limitations of such a hybrid model by comparing data on fragmentation at low relativistic SIS/GSI-energies.

Formation of double-Λ hypernuclei at PANDA

Abstract We study the formation of single- and double- Λ hypernuclei in antiproton-induced reactions relevant for the forthcoming PANDA experiment at FAIR. We use the Giessen Boltzmann–Uehling–Uhlenbeck (GiBUU) transport model with relativistic mean-fields for the description of non-equilibrium dynamics and the statistical multifragmentation model (SMM) for fragment formation. This combined approach describes the dynamical properties of strangeness and fragments in low energy p ¯ -induced reactions fairly well. We then focus on the formation of double- Λ hypernuclei in high energy p ¯ -nucleus collisions on a primary target including the complementary Ξ -induced reactions to a secondary one, as proposed by the PANDA Collaboration. Our results show that a copious production of double- Λ hyperfragments is possible at PANDA. In particular, we provide first theoretical estimations on the double- Λ production cross section, which strongly rises with decreasing energy of the secondary Ξ -beam.

Isospin effects on strangeness in heavy-ion collisions

Abstract Kaon properties are studied within the framework of a fully covariant transport approach. The kaon–nucleon potential is evaluated in two schemes, a chiral perturbative approach and an effective One-Boson-Exchange model. Isospin effects are explicitly accounted for in both models. The transport calculations indicate a significant sensitivity of momentum distributions and total yields of K 0 , + isospin states on the choice of the kaon–nucleon interaction. Furthermore, isospin effects are rather moderate on absolute kaon yields, but appear on strangeness ratios. This is an important issue in determining the high density symmetry energy from studies of strangeness production in heavy-ion collisions.

Asymmetric colliding nuclear matter approach in heavy ion collisions

Abstract The early stage of a heavy ion collision is governed by local non-equilibrium momentum distributions which have been approximated by colliding nuclear matter configurations, i.e., by two Lorentz elongated Fermi ellipsoids. This approach has been extended from the previous assumption of symmetric systems to asymmetric 2-Fermi sphere configurations, i.e., to different densities. This provides a smoother transition from the limiting situation of two interpenetrating currents to an equilibrated system. The model is applied to the dynamical situations of heavy ion collisions at intermediate energies within the framework of relativistic transport (RBUU) calculations. We find that the extended colliding nuclear matter approach is more appropriate to describe collective reaction dynamics in terms of flow observables, in particular, for the elliptic flow at low energies.

In-medium effects on hypernuclear formation

Abstract We study strangeness dynamics in reactions relevant for the formation of multi-strange hypernuclei. In particular, we discuss the in-medium effects on elementary hyperon–nucleon ( YN ) channels, which are relevant for the production of hypernuclei at PANDA. The results indicate strong in-medium effects on YN -scattering, which might be important for hypernuclear studies at PANDA.

Strangeness production in antiproton-nucleus annihilation

The results of the microscopic transport calculations of ¯-nucleus interac- tions within a GiBUU model are presented. The dominating mechanism of hyperon pro- duction is the strangeness exchange processes ¯ KN! Yand ¯ KN! �K. The calculated rapidity spectra ofhyperons are significantly shifted to forward rapidities with respect to the spectra of S =−1 hyperons. We argue that this shift should be a sensitive test for the possible exotic mechanisms of ¯-nucleus annihilation. The production of the double �-hypernuclei by � − interaction with a secondary target is calculated.

Dynamics of phase transitions in asymmetric nuclear matter

Abstract We present several possibilities offered by the reaction dynamics of dissipative heavy ion collisions to study in detail the symmetry term of the nuclear equation of state, EOS . In particular we discuss isospin effects on the nuclear liquid-gas phase transition, Isospin Distillation , and on collective flows. We stress the importance of a microscopic relativistic structure of the effective interaction in the isovector channel. The possibility of an early select Eleven observables, in different beam energy regions, that appear rather sensitive to the isovector part of the nuclear EOS , in particular in more exclusive experiments.