Impact parameter dependence of the scaling of anisotropic flows in intermediate energy heavy-ion collisions

The scaling behaviors of anisotropic flows of light charged particles are studied for 25 MeV/u40Ca+40Ca collisions at different impact parameters by the isospin-dependent quantum molecular dynamics model.The nucleonnumber scaling of elliptic flow exists and the scaling of the ratios of v4/v22and v3/(v1v2)is applicable to collisions at almost all impact parameters except for peripheral collisions.     

Dependence of particle production in high energy heavy ion collisions on the nuclear equation of state

Recent experimental results for ₈₁ ¹⁹⁶ Tl₁₁₅ along with that of ₈₁ ¹⁹⁸ Tl₁₁₅ are analysed. It is shown that staggering observed in the excitation energy of the even and odd spin states in these odd-odd mass transitional nuclei is due to the residual interaction between the two odd particles.     

The high-density symmetry energy in heavy ion collisions

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 relevant experimental data exist. We discuss observables which could yield information on this question, in particular, proton-neutron flow differences, and the production of pions and kaons in relativistic heavy ion collisions. For the meson production we investigate particularly ratios of the corresponding isospin partners π⁻/π⁺ and K⁰/K⁺, where we find that the kaons are an interesting probe to the symmetry energy. In this case we also discuss the influence of various choices for the kaon potentials or in-medium effective masses.     

Light particle correlations in intermediate energy heavy ion collisions

Various light particle coincidence techniques will be reviewed that were employed to study the emission of energetic light particles in nucleus-nucleus collisions at energies above 10 MeV/nucleon. Several reaction mechanisms have been shown to contribute to the emission of energetic light particles, ranging from the sequential statistical decay of excited projectile residues, direct breakup and knock-out reactions, to multistep emission processes that can be rather well described in terms of the concept of local thermal equilibrium.     

Azimuthal correlations between directed and elliptic flow in heavy ion collisions

A method for investigating the azimuthal correlations between directed and elliptic flow in heavy ion collisions is described.The transverse anisotropy of particle emission at AGS energies is investigated within the RQMD model.It is found that the azimuthal correlations between directed and elliptic flow are sensitive to the incident energy and impact parameter.The fluctuations in the initial stage and dynamical evolution of heavy ion collisions are not negligible.     

Role of nuclear surface vibrations in low energy heavy ion collisions

Nuclear surface vibrations cause dissipation as well as fluctuations of the relative motion between heavy ions. Viewing these as transport phenomena, we derive explicit formulae for the induced force and the correlation functions in terms of the spectrum of the nuclear vibrations and the coupling form factor. We provide a general proof that the path integral approach and the density operator formalism lead to equivalent transport coefficients as long as the influence functional takes a standard form. As an illustration, we then analyze⁸⁴Sr+²⁰⁸Pb scattering. We discuss the properties of the potential renormalization, and explain the mechanism of the high lying vibrations becoming dominant in dissipation with increasing bombarding energy by examining the properties of the retarded friction function.     

Two-pion interferometry in heavy ion collisions at HIRFL-CSR energy

We examine the two-pion Hanbury-Brown-Twiss (HBT) interferometry for the particle-emitting source produced in heavy ion collisions at HIRFL-CSR energy. The source evolution is described by relativistic hydrodynamics with three kinds of equations of state for chemical equilibrium (CE), chemical freeze-out (CFO),and partial chemical equilibrium (PCE) models, respectively. We investigate the effects of particle decay,multiple scattering, and source collective expansion on the two-pion interferometry results. We find that the HBT radii of the evolution source for the CFO and PCE models are smaller than that for the CE model.The HBT lifetime for the CFO model is smaller than those for the PCE and CE models. The particle decay increases the HBT radius and lifetime while the source expansion decreases the HBT radius. The multiple scattering effect on the HBT results can be neglected based on our model calculations.     

Jet-photon conversion with energy loss in heavy ion collisions

The rate of high energy photons produced from energetic jets during their propagation through the QGP at RHIC and LHC is studied by taking into account the contribution of jet quenching in the medium. It is shown that the jet quenching effect reduces the rate of jet-photon conversion at large transverse momemtum by about 40% at RHIC with √S＝ 200 AGeV, and by about 80% at LHC with √S = 5500 AGeV.     

Mean field approach to pion production in intermediate energy heavy ion collisions

The pion production in intermediate-energy heavy ion collisions is studied in the mean field approximation. Pion spectra are calculated in the slab geometry for various incident energies. It is found that the one-nucleon process cannot explain the observed cross section and that two-nucleon processes are important.     

Isotope analysis in central heavy ion collisions at intermediate energies

Symmetry energy is a key quantity in the study of the equation of state of asymmetric nuclear matter. Heavy ion collisions at low and intermediate energies, performed at Laboratori Nazionali di Legnaro and Laboratori Nazionali del Sud, can be used to extract information on the symmetry energy coefficient C_sym, which is currently poorly known but relevant both for astrophysics and for deeper knowledge of the structure of exotic nuclei.     

Shadowing effects and transverse momentum dependence of particle emission in intermediate energy heavy ion collisions

Light particle emission was studied at Ganil for ³⁶ Ar +²⁷ Al between 55 and 95 MeV/u and for ⁶⁴ Zn+⁵⁸ Ni between 35 and 79 MeV/u. The correlation of these particles with the reaction plane was analyzed. In intermediate impact parameter events, the transverse momentum dependence of this correlation changes drastically with the energy for midrapidity particles. For both systems, at the upper incident energies, particles with highest transverse momenta are preferentially emitted perpendicular to the reaction plane. This can be qualitatively reproduced by simulations taking into account shadowing effects.     

Energetic proton emission in heavy ion collisions at intermediate energy: Pre-equilibrium and cooperative effects

Energetic proton emission has been investigated as a function of the centrality in the reaction ⁵⁸Ni + ⁵⁸Ni at 30 AMeV. Protons with energy extending up to a relevant fraction of the total available energy in the reaction were measured and studied. The dependence on the reaction centrality has been extensively investigated and data have been compared with the results of microscopic transport calculations. The more striking observation concerns the extremely energetic proton (E^NN _P ≥ 130 MeV) multiplicity which is found to increase almost quadratically with the number of participant nucleons thus indicating the onset of a mechanism beyond one and two-body dynamics.     

Isospin effects of the Skyrme potential and the momentum dependent interaction at intermediate energy heavy ion collisions

We improve the isospin dependent quantum molecular dynamical model by including isospin effects in the Skyrme potential and the momentum dependent interaction to obtain an isospin dependent Skyrme potential and an isospin dependent momentum interaction. We investigate the isospin effects of Skyrme potential and momentum dependent interaction on the isospin fractionation ratio and the dynamical mechanism in intermediate energy heavy ion collisions. It is found that the isospin dependent Skyrme potential and the isospin dependent momentum interaction produce some important isospin effects in the isospin fractionation ratio.     

Density effect of the neutron halo nucleus induced reactions in intermediate energy heavy ion collisions

Using an isospin-dependent quantum molecular dynamics (IQMD) model, we study the 15C induced reactions from 30-120 MeV/nucleon systematically. Here the valence neutron of 15C is assigned at both 1d5/2 and 2s1/2 states respectively in order to study the density effect of reaction mechanism. It is believed that the existent neutron halo structure at the 2s1/2 state of 15C will affect the light particle emission evidently. In our calculation, the different density distributions of 15C at two states are calculated by relativistic mean field (RMF) model and introduced in the initiation of IQMD model, respectively. It is found that some observables such as emission fragmentation multiplicity, emission neutron/proton ratio and emission neutrons’ kinetic energy spectrum are sensitive to the initial density distribution.     

A phenomenological equation of state for isospin asymmetric nuclear matter

A phenomenological momentum-independent(MID) model is constructed to describe the equation of state(EOS) for isospin asymmetric nuclear matter,especially the density dependence of the nuclear symmetry energy Esym(ρ).This model can reasonably describe the general properties of the EOS for symmetric nuclear matter and the symmetry energy predicted by both the sophisticated isospin and momentum dependent MDI model and the Skyrme-Hartree-Fock approach.We find that there exists a nicely linear correlation betwee...     

Strong enhancement of extremely energetic proton production in central heavy ion collisions at intermediate energy

The energetic proton emission has been investigated as a function of the reaction centrality for the system (58)Ni + (58)Ni at 30A MeV. Extremely energetic protons (E(NN)(p) > or = 130 MeV) were measured and their multiplicity is found to increase almost quadratically with the number of participant nucleons, thus indicating the onset of a mechanism beyond one- and two-body dynamics.     

Strangeness enhancement and energy dependence in heavy ion collisions

The canonical statistical model analysis of strange and multistrange hadron production in central A–A relative to p–p/p–A collisions is presented over the energy range from GeV up to GeV. It is shown that the relative enhancement of strange particle yields from p–p/p–A to A–A collisions substantially increases with decreasing collision energy. It is largest at GeV, where the enhancement of and is of the order of 100, 20 and 3, respectively. In terms of the model these results are due to the canonical suppression of particle thermal phase space at lower energies, which increases with the strangeness content of the particle and with decreasing size of the collision fireball. The comparison of the model with existing data on the energy dependence of the kaon/pion ratio is also discussed. Received: 25 October 2001 / Published online: 5 July 2002