J. Rizzo

Isospin emission and flow at high baryon density: A test of the symmetry potential

High-energy heavy-ion collisions are studied to access nuclear-matter properties at high density. Particular attention is paid to the selection of observables sensitive to the poorly known symmetry energy at high baryon density, of large fundamental interest, even for the astrophysics implications. Using fully consistent transport simulations built on effective theories, we test isospin observables ranging from nucleon and cluster emissions to collective flows (in particular the elliptic, squeeze-out, part). The effects of the competition between stiffness and momentum dependence of the symmetry potential on the reaction dynamics are thoroughly analyzed. In this way we try to shed light on the controversial neutron and proton effective mass splitting at high baryon and isospin densities. New, more exclusive, experiments are suggested.

Transport properties of isospin effective mass splitting

Abstract We investigate in detail the momentum dependence (MD) of the effective in medium nucleon–nucleon (NN) interaction in the isovector channel. We focus the discussion on transport properties of the expected neutron–proton (n/p) effective mass splitting at high isospin density. We look at observable effects from collective flows in heavy ion collisions (HIC) of charge asymmetric nuclei at intermediate energies. Using microscopic kinetic equation simulations nucleon transverse and elliptic collective flows in Au+Au collisions are evaluated. In spite of the reduced charge asymmetry of the interacting system interesting isospin-MD effects are revealed. Good observables, particularly sensitive to the n/p mass splitting, appear to be the differences between neutron and proton flows. The importance of more exclusive measurements, with a selection of different bins of the transverse momenta ( p t ) of the emitted particles, is stressed. In more inclusive data a compensation can be expected from different p t -contributions, due to the microscopic isospin-MD structure of the nuclear mean field in asymmetric matter.

Fast nucleon emission as a probe of the momentum dependence of the symmetry potential

In this article we investigate the structure of the non-local part of the symmetry term, that leads to a splitting of the effective masses of protons and neutrons in asymmetric matter. Based on microscopic transport simulations we suggest some rather sensitive observables in collisions of neutron-rich (unstable) ions at intermediate (

Comparison of multifragmentation dynamical models

RIA

Isospin Dynamics in Heavy Ion Collisions: EoS-sensitive Observables

) energies. In particular we focus the attention on pre-equilibrium nucleon emissions. We discuss interesting correlations between the N/Z content of the fast emitted particles and their rapidity or transverse momentum, that show a nice dependence on the prescription used for the effective mass splitting.

On the splitting of nucleon effective masses at high isospin density: reaction observables

Multifragmentation scenarios, as predicted by antisymmetrized molecular dynamics (AMD) or momentum-dependent stochastic mean-field (BGBD) calculations are compared. While in the BGBD case fragment emission is clearly linked to the spinodal decomposition mechanism, i.e. to mean-field instabilities, in AMD many-body correlations have a stronger impact on the fragmentation dynamics and clusters start to appear at earlier times. As a consequence, fragments are formed on shorter time scales in AMD, on about equal footing of light particle pre-equilibrium emission. Conversely, in BGBD pre-equilibrium and fragment emissions happen on different time scales and are related to different mechanisms.

INVESTIGATION OF LOW-DENSITY SYMMETRY ENERGY VIA NUCLEON AND FRAGMENT OBSERVABLES

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.

Probing the nuclear EOS with fragment production

We review the present status of the nucleon effective mass splitting puzzle in asymmetric matter, with controversial predictions within both non‐relativistic and relativistic approaches to the effective in medium interactions. Based on microscopic transport rimulations we suggest some rather sensitive observables in collisions of asymmetric (unstable) ions at intermediate (RIA) energies: i) Energy systematics of Lane Potentials; ii) Isospin content of fast emitted nucleons; iii) Differential Collective Flows. Similar measurements for light isobars (like 3H−3He) could be also important.

Isospin Dynamics in Heavy Ion Collisions: from Coulomb Barrier to Quark Gluon Plasma

There has been much interest in recent years in the determination of the nuclearsymmetry energy as a function of density, which is important for the structure ofexoticnucleiaswellasforastrophysicalprocesses.Heavyioncollisions(HIC) presentan attractive way to constrain the the existing models for this poorly-determinedisovector equation-of-state (iso-EOS),

CONSTRAINING THE SYMMETRY ENERGY: A JOURNEY IN THE ISOSPIN PHYSICS FROM COULOMB BARRIER TO DECONFINEMENT

Abstract We discuss fragmentation mechanisms and isospin transport occurring in central collisions between neutron rich systems at Fermi energies. In particular, isospin effects are analyzed looking at the correlations between fragment isotopic content and kinematical properties. Simulations are based on an approximate solution of the Boltzmann-Langevin (BL) equation. An attempt to solve the complete BL equation, by introducing full fluctuations in phase space is also discussed.