Pre-equilibrium effects and neck emission in 10-40 AMeV heavy ion collisions

New experimental results on pre-equilibrium effects and neck emission at Fermi energies are presented. Coulomb trajectory calculations have been performed to explain the observed IMF velocity distributions.     

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.     

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.     

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.     

中能重离子碰撞中晕核反应动力学

基于同位旋相关量子分子动力学研究了中子晕核和质子晕核的核反应动力学，着重研究了松散的晕结构对于重离子碰撞中的碎裂和动量耗散中的特殊作用. 为了突出晕核松散结构在反应动力学中的特殊作用. 同时计算了在完全相同入射道条件下相等质量稳定弹核引起核反应. 通过对晕核和稳定核核反应动力学结果的对比分析，发现晕核的松散结构对核反应动力学的作用和影响是重要的. 如这种松散结构明显的增加了碎裂多重性；相反, 减小了原子核阻止(动量耗散). 关键词： 中子晕核 质子晕核 重离子碰撞 核反应动力学     

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.     

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.     

Pre-equilibrium light particle emission in heavy ion induced reactions

We derive a master equation to describe the time evolution of the intrinsic state in heavy-ion collisions. It takes into account the energy supply from the relative motion due to the one-body dissipation mechanism, and the equilibration process and the particle emission due to the two-body residual interaction. We then calculate the energy spectrum and the angular distribution of the emitted protons in¹⁴N,¹⁶O andα induced reactions for various targets and incident energies. The angular distribution is calculated based on a simple phase-space consideration. The numerical results agree very well with experimental data.     

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.     

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.     

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     

A guide to microscopic models for intermediate energy heavy ion collisions

In the last few years heavy ion experiments have addressed key questions regarding the behavior of nuclear matter at high excitation and density. Simultaneous progress in theory has been achieved by the formulation of calculational tools to apply microscopic models to experimental observables. The present review covers a large part of this theoretical development. We provide enough details so that the uninitiated but interested reader can arrive at the present status of the theory and its relationship to current experiments. The energy range of interest here is 50 MeV/n lab to 1 GeV/n lab.     

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.     

Partonic effects in heavy ion collisions at RHIC

Effects of partonic interactions in heavy ion collisions at RHIC are studied in a multiphase transport model (AMPT) that includes both initial partonic and final hadronic interactions. It is found that a large parton scattering cross section is needed to understand the measured elliptic flow of pions and two-pion correlation function.     

High energy heavy ion collisions: Lessons from relativistic heavy ion collider

In this talk, I review the recent results from RHIC and discuss their significance.     

Composite particle emission in relativistic heavy ion collisions

Inclusive spectra of d, t, and ³He have been measured over a wide range of fragment angles and energies. The observed spectra are well reproduced by the “coalescence model” with a coalescence radius p₀ which is independent of beam energies and which decreases as the sizes of the target-projectile combinations increase. The sizes of the interaction regions have been derived from these p₀ values. The experimental cross sections generally deviate from predictions of the firestreak model.     

Preequilibrium emission in heavy ion collisions: A dynamical approach

A coupled treatment of both dynamics and G.D.H. Model is proposed to treat “prior equilibration” phase in heavy ion collisions. Assumptions and coupling effects are discussed in details, and a numerical procedure is developped. Comparison with²⁷A1(¹⁴N,X) at energies standing from 7–30 MeV/nucleon is presented. Proton and helium 4 productions, angle integrated spectra and angular distributions are compared. Incomplete fusion to fusion ratio is correctly reproduced in the intermediate incident energy region. A part of the linear momentum lost can be explained and a non negligeable transverse momentum is predicted for the fusion events. Differents types of experimental data are needed to test the validity of this approach and further developments are discussed.     

Scaling of anisotropic flows and nuclear equation of state in intermediate energy heavy ion collisions

Elliptic flow ($v_2$) and hexadecupole flow ($v_4$) of light clusters have been studied in detail for 25 MeV/nucleon $^{86}$Kr + $^{124}$Sn at large impact parameters by using a quantum molecular dynamics model with different potential parameters. Four sets of parameters including soft or hard equation of state (EOS) with or without symmetry energy term are used. Both number-of-nucleon ($A$) scaling of the elliptic flow versus transverse momentum ($p_{\rm t}$) and the scaling of $v_4/A^{2}$ versus $(p_{\rm t}/A)^2$ have been demonstrated for the light clusters in all above calculation conditions. It is also found that the ratio of $v_4/{v_2}^2$ maintains a constant of 1/2 which is independent of $p_{\rm t}$ for all the light fragments. Comparisons among different combinations of the EOS and the symmetry potential term show that the above scaling behaviours are sound and independent of the details of potential, while the strengths of flows are sensitive to the EOS and the symmetry potential term.