Classical many-body model for heavy-ion collisions: (III). Ne-Ne and Ca-Ca calculations

The classical many-body model, previously introduced, has been employed to perform numerical calculations of systems consisting of 20 on 20 and 40 on 40 nucleons. Comparison is made with the 800A MeV data of Nagamiya, et al. Microscopic time development of the system and central compressions are displayed for Ca on Ca. Microscopic comparions with the fireball/firestreak models are presented; although qualitative agreement is found, interesting and expected shortcomings in the latter were seen. In particular, the classical many-body model exhibits shear viscosity and incomplete thermalization.     

Classical microscopic calculation of fast heavy-ion collisions

We consider heavy-ion collisions with beam energies of a few hundred MeV/nucleon, because such collisions seem favorable for producing compressed nuclear matter. As an alternative to hydrodynamic ways of calculating such collisions, we are investigating a microscopic, rapid (and therefore economical) simulation method. There are two simplifications basic to this method: (i) using classical particle kinematics, and (ii) taking nucleonnucleon interactions into account via cross sections rather than explicit forces. Some other simplifications, concerning nuclear binding etc., are presently crude but will be improved. Even at normal density, nuclear matter is not so dilute; therefore our calculations show some sensitivity to details of the mechanism assume for nucleon-nucleon scattering. For head-on collision of two mass-235 nuclei, our present calculations yield maximum densities between 2 and 3 times that of normal nuclear matter.     

Stochastic time-dependent hartree-fock for heavy-ion collisions at fermi energies

We present the first application of Stochastic Time-Dependent Hartree-Fock for describing realistic heavy-ion collisions in the Fermi energy domain. We discuss the robustness of the collision scheme and show some examples of application. Presented by E. Suraud at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Classical many-body model for heavy-ion collisions (II)

A four-parameter classical many-body model, specifically designed for heavy-ion collisions, is presented. Binding energies and densities of infinite and finite nuclei (N = Z) are satisfactorily reproduced. So also is the viscosity moment of the two-body scattering cross section at lab energies between 100 and 300 MeV.     

Classical many-body model for heavy-ion collisions incorporating the Pauli principle

A classical model for heavy-ion collisions, introduced previously, has been extended to include certain effects of the Pauli principle. All nucleons are treated equally. They obey classical dynamics and interact through an ordinary two-body force and through a momentumdependent two-body “Pauli core” which satisfies, approximately, that $\text{p}{}_{\mathrm{ij}}\text{r}{}_{\mathrm{ij}}\text{≧ξ}\text{h}\text{?}$, where ξ is a dimensionless constant. A form for the Pauli core is presented. The ordinary two-body force has been adjusted to fit bulk properties of nuclei and to reproduce that moment of nucleon nucleon scattering cross sections which is relevant to hydrodynamics. The parameters of the forces are given.     

Preequilibrium nucleon jets in TDHF calculations of medium-energy,heavy-ion collisions

We study collisions of ¹²C and ¹⁹⁷Au projectiles at E_lab/A_proj = 30 to 85 MeV/A on ¹⁹⁷Au targets, using the 3-dimensional TDHF model. Most of the qualitative phenomena observed experimentally are reproduced by the TDHF calculations. The results are compared with recent data from the 1 GeV ¹²C beam at CERN and show some quantitative deviations from experiment. Possible reasons for these discrepancies are discussed and give valuable insight into intermediate energy collision processes.     

On the mass distribution in Time-Dependent Hartree-Fock calculations of heavy-ion collisions

In previous papers we have introduced a simple model for backbending nuclei which satisfactorily describes the essential experimental features of those nuclei. In this paper we show that the basic assumptions of this model can be deduced by a more microscopic treatment.     

Photon production in relativistic heavy-ion collisions using rates with two-loop calculations from quark matter

The production of single photons in relativistic heavy-ion collisions at CERN SPS, BNL RHIC and CERN LHC energies is re-examined in view of the recent studies of Aurenche et al., which show that the rate of photon production from quark–gluon plasma evaluated at the order of two loops by far exceeds the rates evaluated at the one-loop level, which have formed the basis of all the estimates of photons so far. We find that the production of photons from quark matter could easily outshine those from the hadronic matter under certain ideal conditions. Received: 6 April 1999 / Revised version: 30 April 1999 / Published online: 8 September 1999     

Bremsstrahlung in heavy-ion collisions

The bremsstrahlung background emission of γ-rays in equal-mass heavy-ion collisions is calculated. The cross section is found to be about an order of magnitude smaller than preliminary upper limits of ¹²C-¹²C experiments in progress.     

Flavor-dependent photoproduction in heavy-ion collisions

Strong electromagnetic fields produced in the non-central heavy-ion collisions can induce vector meson photoproduction. In this paper, we study the photoproduction J/ψ and φ mesons in the relativistic heavy-ion collision from ultra-peripheral nuclear collisions to peripheral hadronic heavy ion collisions. And then include both initial hadronic production and thermal production in quark-gluon plasma (QGP). We find, for the charm anti-charm bound state J/ψ, the photoproduced J/ψs are mainly in the very low momentum region and clearly exceed the hadronic production. However, considering the thermal production of strange quark anti-quark pairs in QGP produced in relativistic heavy-ion collisions, the photoproduced φ is usually smaller than the thermal production and only evident at very peripheral collisions as even their photoproduction is much larger than J/ψ.     

Seeing jets in heavy-ion collisions

In these proceedings, we briefly review how jets can be reconstructed in heavy-ion collisions. The main point we address is the subtraction of the large contamination from the underlying event background. We first present the main ingredients needed to define the jets and perform the background subtraction and then discuss the efficiency of the subtraction for different jet algorithms and background-estimation methods.     

Catalytic reactions in heavy-ion collisions

We discuss a new type of reactions of a ?-meson production on hyperons, ??Y ?? ?Y and antikaons -KN ?? ?Y. These reactions are not suppressed according to Okubo-Zweig-Iizuka rule and can be a new efficient source of ? mesons in a nucleus-nucleus collision. We discuss how these reactions can affect the centrality dependence and the rapidity distributions of the ? yield.     

Quarkochemistry in relativistic heavy-ion collisions

The time necessary to achieve the equilibrium ratio of strange to non-strange quarks in heavy-ion reactions is estimated in the framework of perturbative QCD. It is found, in the present approximation, to be much larger than the total collision time of even a central U + U collision at E_lab=2.1 GeV/nucleon bombarding energy.     

Molecular configurations in heavy-ion collisions

High spin properties of ²⁴Mg, ³²S and ³⁶S have been studied by means of the Strutinsky method. A separation degree of freedom is explicitly included by using a two-center model for the shellmodel part of the calculations. It is found that for the first two systems special configurations exist that are in their structure directly related to molecular ¹²C + ¹²C and ¹⁶O + ¹⁶O configurations and merge continuously into these with increasing separation. On the basis of these results the general problem of molecular states is discussed.     

Charmonium-state production in heavy-ion collisions

An overview of existing experimental data on the production of charmonium states (J/ψ and ψ′) at the superproton synchrotron (SPS, CERN) and the relativistic heavy ion collider (RHIC, Brookhaven National Laboratory, United States) is given. The production of J/ψ mesons shows an anomalous suppression discovered by the NA50 Collaboration (CERN) in collisions of lead nuclei at an energy of 158 GeV per nucleon and confirmed in the NA60 experiment (CERN) in collisions of indium nuclei at the same energy. The suppression of J/ψ production depends on interaction centrality and becomes anomalous at about 122 participant nucleons in PbPb collisions and at about 86 participant nucleons in InIn collisions. The experimental data in question are compared with the predictions of existing theoretical models. None of the models is able to simultaneously describe data on PbPb and InIn collisions. Data obtained in the PHENIX experiment at RHIC from measurements of J/ψ production in AuAu and CuCu collisions at an energy of 200 GeV (in the nucleon-nucleon c.m. frame) indicate that the suppression of J/ψ production at such energies approximately corresponds to the suppression of J/ψ production in PbPb collisions at SPS. Theoretical models that describe SPS data on PbPb collisions predict a stronger suppression of J/ψ production. Models that take into account J/ψ-meson regeneration better describe experimental data obtained at RHIC. Measurement of cross sections for charmonium and bottomonium production at the Large Hadron Collider (LHC, CERN) would make it possible to study the properties of matter and to explore the mechanism of quarkonium production at ultrahigh energy densities and temperature and high transverse momenta, as well as to investigate the effect of the regeneration and suppression of quarkonium production as the energy increases.     

Anomalons in relativistic heavy-ion collisions

By reviewing experimental results from many anomalon searches, one can reasonably conclude that anomalons, if they exist, are preferentially produced in peripheral collisions, signified by low values of N_h and δZ. For Z ≥ 3, the experimental picture about the existence of anomalons is not very clear at this moment. In the Z = 2 case, however, there are reasonably convincing indications that anomalons do seem to be present in fragments produced by light projectile nuclei such as ¹²C.     

Dynamical instabilities in heavy-ion collisions

Within the σ-ω model for nuclear matter, an instability in a system of two counterstreaming fluids is discussed. This instability leads, if developed, to a separation of the two currents in space — a periodic structure orthogonal to the beam axis is finally obtained. In contrast to previous results by Ivanov, the maximal growth rate for the instability is shown to occur at a finite wavelength. Furthermore, these growth rates are much lower than calculated before. The influence of vacuum contributions is also discussed.