Isospin effects in intermediate energy heavy ion collisions (original) (raw)
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The high-density symmetry energy in heavy ion collisions
Progress in Particle and Nuclear Physics, 2009
The nuclear symmetry energy as a function of density is rather poorly constrained theoretically and experimentally both below saturation density, but particularly at high density, where very few relaevant experimental data exist. We discuss observables which could yield information on this question, in particular, proton-neutron flow differences, and the production of pion and kaons in relativistic heavy ion collisions. For the meson production we investigate particularly ratios of the corresponding isospin partners π − /π + and K 0 /K + , where we find that the kaons are an interesting probe to the symmetry energy. In this case we also discuss the influnece of various choices for the kaon potentials or in-medium effective masses.
Relativistic effects in the search for high density symmetry energy
Physics Letters B, 2003
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.
On the Lorentz structure of the symmetry energy
Nuclear Physics A, 2004
We investigate in detail the density dependence of the symmetry energy in a relativistic description by decomposing the iso-vector mean field into contributions with different Lorentz covariant properties. We find important effects of the iso-vector, scalar channel (i.e. δ-meson like) on the high density behavior of the symmetry energy. Applications to static properties of finite nuclei and to dynamic situations of heavy ion collisions are explored and related to each other. The nuclear structure studies show only moderate effects originating from the virtual δ meson. At variance, in heavy ion collisions one finds important contributions on the reaction dynamics arising from the different Lorentz structure of the high density symmetry energy when a scalar iso-vector δ field is introduced. Particularly interesting is the related neutron/proton effective mass splitting for nucleon transport effects and for resonance and particle production around the threshold. We show that the δ-like channel turns out to be essential for the production of pions, when comparing with experimental data, in particular for high momentum selections.
Probing the Symmetry Energy at High Baryon Density with Heavy Ion Collisions
International Journal of Modern Physics E, 2010
The nuclear symmetry energy at densities above saturation density (ρ0 ~ 0.16fm-3) is poorly constrained theoretically and very few relevant experimental data exist. Its study is possible through Heavy Ion Collisions (HIC) at energies E/A > 200 MeV , particularly with beams of neutron-rich radioactive nuclei. The energy range implies that the momentum dependence of the isospin fields, i.e. the difference of the effective masses on protons and neutrons, also has to be investigated before a safe constraint on E sym (ρ) is possible. We discuss the several observables which have been suggested, like n/p emission and their collective flows and the ratio of meson yields with different isospin projection, π-/π+ and K0/K+. We point out several physical mechanisms that should be included in the theoretical models to allow a direct comparison to the more precise experiments which will be able to distinguish the isospin projection of the detected particles: CSR/Lanzhou, FAIR/GSI, RIBF/RIKEN,...
Stopping and isospin equilibration in heavy ion collisions
Physics Letters B, 2004
We investigate the density behaviour of the symmetry energy with respect to isospin equilibration in the combined systems Ru(Zr) + Zr(Ru) at relativistic energies of 0.4 and 1.528 AGeV . The study is performed within a relativistic framework and the contribution of the iso-vector, scalar δ field to the symmetry energy and the isospin dynamics is particularly explored. We find that the isospin mixing depends on the symmetry energy and a stiffer behaviour leads to more transparency. The results are also nicely sensitive to the "fine structure" of the symmetry energy, i.e. to the covariant properties of the isovector meson fields.
Probing the nuclear symmetry energy with heavy-ion collisions
Journal of Physics G: Nuclear and Particle Physics, 2010
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation. In this report we present a selection of new reaction observables in dissipative collisions particularly sensitive to the symmetry term of the nuclear Equation of State (Iso − EoS). We will first discuss the Isospin Equilibration Dynamics. At low energies this manifests via the recently observed Dynamical Dipole Radiation, due to a collective neutron-proton oscillation with the symmetry term acting as a restoring force. At higher beam energies Iso-EoS effects will be seen in an Isospin Diffusion mechanism, via Imbalance Ratio Measurements, in particular from correlations to the total kinetic energy loss. For fragmentation reactions in central events we suggest to look at the coupling between isospin distillation and radial flow. In Neck Fragmentation reactions important Iso − EoS information can be obtained from fragment isospin content, velocity and alignement correlations.
Isospin correlations in high-energy heavy-ion collisions
1994
We study the posibility of large isospin fluctuations in high-energy heavy-ion collisions by assuming that pions are produced semiclassically both directly and in pairs through the isovector channel. The leading-particle effect and the factorization property of the scattering amplitude in the impact parameter space are used to define the classical pion field. In terms of the joint probability function PII3(n0,n)P_{II_{3}}(n_{0},n_{\_})PII3(n0,n) for producing n0n_{0}n0 neutral and nn_{\_}n negative pions from a definite isospin state II3II_{3}II3 of the incoming leading-particle system we calculate the two pion correlation parameters f2,n0f_{2,n_{\_}}^{0}f2,n0 and the average number of neutral pions (n)( _{n_{\_}})(n) as a function of negative pions (n)(n_{\_})(n) produced. We show that only direct production of pions without isovector pairs leads to large isospin fluctuations.
Isospin dynamics in heavy ion collisions: From Coulomb barrier to quark gluon plasma
Progress in Particle and Nuclear Physics, 2009
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation. In this report we present a selection of new reaction observables in dissipative collisions particularly sensitive to the symmetry term of the nuclear Equation of State (Iso − EoS). We will first discuss the Isospin Equilibration Dynamics. At low energies this manifests via the recently observed Dynamical Dipole Radiation, due to a collective neutronproton oscillation with the symmetry term acting as a restoring force. At higher beam energies Iso-EoS effects will be seen in Imbalance Ratio Measurements, in particular from the correlations with the total kinetic energy loss. For fragmentation reactions in central events we suggest to look at the coupling between isospin distillation and radial flow. In Neck Fragmentation reactions important Iso − EoS information can be obtained from the correlation between isospin content and alignement. The high density symmetry term can be probed from isospin effects on heavy ion reactions at relativistic energies (few AGeV range). Rather isospin sensitive observables are proposed from nucleon/cluster emissions, collective flows and meson production. The possibility to shed light on the controversial neutron/proton effective mass splitting in asymmetric matter is also suggested. A large symmetry repulsion at high baryon density will also lead to an "earlier" hadron-deconfinement transition in n-rich matter. A suitable treatment of the isovector interaction in the partonic EoS appears very relevant.
International Journal of Modern Physics E-nuclear Physics, 2008
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium nuclear interaction in regions away from saturation. In this work we present a selection of reaction observables in dissipative collisions 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