Time-dependent Hartree-fock description of charge equilibration in heavy-ion collisions (original) (raw)
Pre-equilibrium dipole strength excitation in dissipative heavy-ion collisions
Nuclear Physics A, 1995
PACS numbers: 25. 24.30.Cz, 25.70.Lm The study of the evolution of the properties of the giant dipole resonance (GDR) as a function of the excitation energy has been a major field of interest in the last years 1 . While the GDR resonance energy remains approximately constant over a large range of excitation energy, both its width and strength change. In the experimental data the former increases up to about twice the ground state value and the latter shows a saturation at high excitation energy. These outcomes stimulated the formulation of several models which could justify the experimental data2, 3. In this framework it was also pointed out that a significant amount of dipole strength could be excited at the very early stages of the nuclear interaction leading to preequilibrium giant dipole '~-ray emission. Two mechanisms have been proposed which could support such a possibility: the existence of a dipole moment due to the charge asymmetry between the reaction partners and the mass asymmetry in the entrance channel2, 4. In this paper we report on the first experimental evidences of preequilibrium giant dipole 7-raY emission from the intermediate systems produced in the 35C1+64Ni and 35C1+92M0 reactions at a collision energy of 271 and 260 MeV respectively. The results relative to the last reaction have to be considered to some extent as preliminary being the analysis still in progress. The 35CI pulsed beam of the superconducting heavy-ion linear accelerator of the CEA-DAPNINDPhN of Saclay (France), impinging on a self supporting 64Ni and 92Mo targets about 300 mg/cm 2 thick, was used. Coincidence spectra between 7-rays and complex fragments produced through a dissipative reaction mechanism were measured. The coincidence y-ray spectra include the photons coming from the decay of the intermediate system before its fragmentation in addition to those coming from the Elsevier Science B.V. SSDI 0375-9474(94)00644-X
D ec 2 01 1 Remarks on the non-equilibrium effects and collision dynamics in heavy-ion collisions
2018
We study the beam energy dependence of equilibration process and space-time characteristics of participant and spectator matter. For this, we simulated the semi-central collisions of Ca+ Ca at incident energies of 400, 600 and 1000 AMeV within the quantum molecular dynamics (QMD) approach. Our numerical calculations based on the molecular dynamics approach show that incident energy of the projectile influences the reaction observables drastically. The effect is more visible for transverse expansion of the nuclear matter and transparency behavior. The degree of thermalization of participant matter, however, remains independent of the incident energy. The characteristics of the trajectories followed by the nucleons suffering maximal and minimal binary collisions are also analyzed.
The dynamical dipole mode in dissipative heavy-ion collisions
Nuclear Physics A, 2001
We study the effect of a direct Giant Dipole Resonance (GDR) excitation in intermediate dinuclear systems with exotic shape and charge distributions formed in charge asymmetric fusion entrance channels. A related enhancement of the GDR gamma yield in the evaporation cascade of the fused nucleus is expected. The dynamical origin of such GDR extra strength will show up in a characteristic anisotropy of the dipole gamma-emission. A fully microscopic analysis of the fusion dynamics is performed with quantitative predictions of the GDR photon yield based on a dynamics-statistics coupling model. In particular we focus our attention on the energy and mass dependence of the effect. We suggest a series of new experiments, in particular some optimal entrance channel conditions. We stress the importance of using the new available radioactive beams.
Remarks on the non-equilibrium effects and collision dynamics in heavy-ion collisions
Physica Scripta, 2010
We study the beam energy dependence of equilibration process and space-time characteristics of participant and spectator matter. For this, we simulated the semi-central collisions of 40 Ca + 40 Ca at incident energies of 400, 600 and 1000 AMeV within the quantum molecular dynamics (QMD) approach. Our numerical calculations based on the molecular dynamics approach show that incident energy of the projectile influences the reaction observables drastically. The effect is more visible for transverse expansion of the nuclear matter and transparency behavior. The degree of thermalization of participant matter, however, remains independent of the incident energy. The characteristics of the trajectories followed by the nucleons suffering maximal and minimal binary collisions are also analyzed.
Physical Review C, 2007
Results from electric charge correlations studied with the Balance Function (BF) method in A+A collisions from 20A to 158A GeV are presented in two different rapidity intervals: In the midrapidity region we observe a decrease of the width of the BF distribution with increasing centrality of the collision, whereas this effect vanishes in the forward rapidity region. Results from the energy dependence study in central Pb+Pb collisions show that the narrowing of the BF expressed by the normalized width parameter W increases with energy toward the highest CERN Super Proton Synchrotron and BNL Relativistic Heavy Ion Collider energies. Finally we compare our experimental data points with the predictions of several models. The hadronic string models Ultra-relativistic Quantum Molecular Dynamics and Heavy Ion Jet INteraction Generator (HIJING) do not reproduce the observed narrowing of the BF. However, A MultiPhase Transport medel (AMPT), which contains a quark-parton transport phase before hadronization, can reproduce the narrowing of the BF's width with centrality. This confirms the proposed sensitivity of the BF analysis to the time of hadronization.
Inner and outer shell contributions to the charge state distribution in heavy ion collisions
Physics Letters A, 1979
The charge distributions of ~+q ions after small impact parameter collisions in the medium energy range -~50 keV/amu, were studied. For symmetric and nearly symmetric systems they display a simple convex structure as a function of the impact parameter. This structure is interpreted as a result of an inner shell promotion effect superimposed on a purely statistical, impact parameter independent distribution. Good agreement with the shape predicted by the rotational coupling model allows the separation of the inner and outer shell contributions to the charge distribution. Charge exchange processes in heavy ion collisions,in ed to be impact parameter dependent according to the the medium energy range, I <v "~Z(au),involve main-MO couplings [5] . In such a case it can be identified
Charge equilibration in heavy-ion reactions at intermediate energies
Physics Letters B, 1997
We investigate the time scale for charge equilibration in heavy-ion collisions at intermediate energies. The dynamics is studied within the framework of the Boltzmann-Uehling-Uhlenbeck approach and two molecular dynamics models which differ on the treatment for the Pauli principle. The BUU description predicts a relatively short time scale for charge equilibration, whereas this process turns out to depend quite sensitively on the prescription used for the Pauli principle in the molecular dynamics calculations. @ 1997 Elsevier Science B.V.
Charge exchange in relativistic heavy-ion collisions
Nuclear Physics A, 2000
Elastic charge-exchange in relativistic heavy ion collisions is responsible for the non-disruptive change of the charge state of the nuclei. We show that it can be reliably calculated within the eikonal approximation for the reaction part. The formalism is applied to the charge-pickup cross sections of 158
Physics of Heavy Ion Collisions
International Journal of Modern Physics E, 2006
This review article covers a variety of phenomena observed in heavy ion collisions in full range of available collisions energies. The main reaction channels characteristic of each energy domain are discussed in conjuction with existing nuclear reaction models. Methods used to extract characteristic features of hot nuclear objects are shown. Relations between properties of microscopic nuclear objects and infinite nuclear matter are presented. At the end of this review the transition between hadronic phase and the strongly interacting quark-gluon plasma is discussed.