Isospin Dynamics in Heavy Ion Collisions: EoS-sensitive Observables

Laboratori Nazionali del Sud INFN, I-95123 Catania, Italy, and Physics-Astronomy Dept., University of Catania; Dept. of Theoretical Physics, Bucharest Univ., Magurele, Bucharest, Romania; Dept. für Physik, Universität München, D-85748 Garching, Germany
Nuclear Physics A (Impact Factor: 2.5). 10/2006; DOI: 10.1016/j.nuclphysa.2006.12.088
Source: arXiv

ABSTRACT Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation and at high nucleon momenta. In this report we present a selection of reaction observables particularly sensitive to the isovector part of the interaction, i.e. to the symmetry term of the nuclear Equation of State (EoS) At low energies the behavior of the symmetry energy around saturation influences dissipation and fragment production mechanisms. Predictions are shown for deep-inelastic and fragmentation collisions induced by neutron rich projectiles. Differential flow measurements will also shed lights on the controversial neutron/proton effective mass splitting in asymmetric matter. The high density symmetry term can be derived from isospin effects on heavy ion reactions at relativistic energies (few AGeV range), that can even allow a “direct” study of the covariant structure of the isovector interaction in the hadron medium. Rather sensitive observables are proposed from collective flows and from pion/kaon production. The possibility of the transition to a mixed hadron-quark phase, at high baryon and isospin density, is finally suggested. Some signatures could come from an expected “neutron trapping” effect.

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    ABSTRACT: Within two different frameworks of isospin-dependent transport model, i.e., Boltzmann-Uehling-Uhlenbeck (IBUU04) and Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport models, sensitive probes of nuclear symmetry energy are simulated and compared. It is shown that neutron to proton ratio of free nucleons, pi-/pi+ ratio as well as isospin-sensitive transverse and elliptic flows given by the two transport models with their "best settings", all have obvious differences. Discrepancy of numerical value of isospin-sensitive n/p ratio of free nucleon from the two models mainly originates from different symmetry potentials used and discrepancies of numerical value of charged pi-/pi+ ratio and isospin-sensitive flows mainly originate from different isospin-dependent nucleon-nucleon cross sections. These demonstrations call for more detailed studies on the model inputs (i.e., the density- and momentum-dependent symmetry potential and the isospin-dependent nucleon-nucleon cross section in medium) of isospin-dependent transport model used. The studies of model dependence of isospin sensitive observables can help nuclear physicists to pin down the density dependence of nuclear symmetry energy through comparison between experiments and theoretical simulations scientifically.
    Physics Letters B 06/2013; 726(1). · 6.02 Impact Factor
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    ABSTRACT: Heavy Ion Collisions play an important role in probing the density dependence of the asymmetry energy by providing a unique tool to probe nuclear interactions away from saturation. Lower energy reactions (~10-15A MeV) provide a means of probing around and below normal nuclear density. In particular, these collisions can provide a sensitive means of probing the interaction and possibly the asymmetry terms of the nuclear Equation of State. Simulations of 124Sn+64Ni using Constrained Molecular Dynamics and Stochastic Mean Field calculations, at different asymmetry energies, have been used to study the asymmetry energy dependence of projectile-like fragment break-up channels as well as the mass correlations of the heaviest fragments. The results of these simulations present the possibility of developing an experimental probe for measuring the density dependence of the asymmetry energy using picosecond time resolution time of flight spectroscopy in a multi-detector array.
    Journal of Physics Conference Series 03/2013; 420(1):2113-.
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    ABSTRACT: The momentum dependence of the medium modifications on nucleon–nucleon elastic cross sections is investigated with the microscopic transport model UrQMD. The semi-peripheral Au+Au collision at the beam energy Eb = 400A MeV is adopted as an example. It is found that uncertainties of the momentum dependence on medium modifications of cross sections visibly influence the yield and collective flow distributions of free nucleons. In these observables, the elliptic flow is sensitively dependent on detailed forms of the momentum dependence. However, it is weakly influenced by the splitting effect of the neutron–neutron and proton–proton cross sections.
    Modern Physics Letters A 11/2011; 25(09). · 1.34 Impact Factor

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