Quantum interference and statistical fluctuations in deep-inelastic heavy-ion reactions

Starting from the general multi-channel formulation of the scattering matrix we perform a coarse-grain average of the cross section appropriate for the observed quantities in heavy-ion reactions. We keep full track of the geometrical factors for the coupling of partial waves and channel spin. Relating the diagonal part of the S-matrix product semiclassically to the statistical treatment in terms of phase-space trajectories we are dealing with quantum fluctuations and statistical fluctuations on an even basis. Quantum corrections play a minor role if the underlying statistical model takes effects of the nonthermalized relative motion properly into account. This is true even for small energy losses.     

Incomplete deep-inelastic heavy-ion collisions

A phenomenological two-step reaction model is proposed, in which a direct projectile fragmentation in the initial stage is succeeded by a binary dissipative interaction between the heavy projectile fragment and the target in the final state. Multi-differential cross sections are estimated by folding the fragmentation cross section given in the local plane-wave Born approximation with the cross section for deep-inelastic collisions calculated within the classical friction model, including statistical fluctuations and mass transfer. For forward angles satisfactory results are obtained in comparison with the experimental data on inclusive spectra, angular distributions, angular correlations, γ-multipliciites, and element distributions in ²⁰Ne-induced reactions for bombarding energies of 10–20 MeV/nucleon.     

High-spin states in neutron-rich nuclei explored with deep-inelastic HI reactions

The use of deep-inelastic heavy-ion reactions for the spectroscopy of neutron-rich nuclei is discussed. Conclusions from the N/Z equilibration process studies are outlined and examples of spectroscopic results obtained for the neutron-rich spdf shell nuclei, N = 82 isotones and nuclei from the ²⁰⁸Pb region are reviewed. Received: 1 May 2001 / Accepted: 4 December 2001     

Probing the nuclear symmetry energy with heavy-ion reactions induced by neutron-rich nuclei

Heavy-ion reactions induced by neutron-rich nuclei provide a unique means to investigate the equation of state of isospin-asymmetric nuclear matter, especially the density dependence of the nuclear symmetry energy. In particular, recent analyses of the isospin diffusion data in heavy-ion reactions have already put a stringent constraint on the nuclear symmetry energy around the nuclear matter saturation density. We review this exciting result and discuss its implications on nuclear effective interactions and the neutron skin thickness of heavy nuclei. In addition, we also review the theoretical progress on probing the high density behaviors of the nuclear symmetry energy in heavy-ion reactions induced by high energy radioactive beams.      

Further studies of large collision residues in relativistic heavy-ion reactions with heavy nuclei

Target residue mass and charge distributions have been measured radiochemically for the reaction of 25.2 GeV ¹²C ions with Au and Pb. Enhanced product yields for A = 140?170 are found that are not present in reactions of Pb with GeV protons. The shape of the mass distribution in this region is used to define a pre-equilibrium product mass distribution.     

Gamma-ray spectroscopy of the neutron-rich Ni region through heavy-ion deep-inelastic collisions

Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T _1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the doubly magic ⁶⁸Ni and its neighbor ^69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed. Received: 1 May 2001 / Accepted: 4 December 2001     

Mesonic processes in deep-inelastic electron scattering from nuclei

Inelastic electron scattering is considered in the energy and momentum transfer region associated with the quasielastic and 3-3 resonance pion electroproduction peaks. Calculations of two-nucleon ejection via two-body meson-exchange currents (MEC) and of pion electroproduction from threshold through the 3-3 resonance are presented using the Fermi gas model of the nucleus. The MEC contribution is found to be significant in this region, and helps to account for the discrepancy between theory and experiment in the “dip” between the quasielastic and 3-3 resonance peaks.     

Dynamical deformation of nuclei participating in deep-inelastic collisions

TheN/Z equilibration process taking place in deep-inelastic heavy ion collisions above the Coulomb barrier was studied by means of thick target gamma spectroscopy method. The analysis of gamma coincidence data obtained for four heavy ion systems gave complete distributions of primary reaction products which allowed to extract the most probableN/Z ratios as a function of mass. The comparison of experimentalN/Z values with expectations based on potential energy minimization leads to conclusion that during the crucial interaction time the involved nuclei are dynamically deformed.     

Neutron-rich nuclei studied with AMD

Antisymmetrized molecular dynamics (AMD) which is a newly constructed theory of quantum-mechanical microscopic simulation of heavy ion collisions is explained to present us with a very useful theoretical approach for the study of the structure-changes which occur when we go from ordinary nuclei to exotic neutron-rich nuclei. It is because of the flexible nature of the AMD wave function which can describe the formation and dissolution of clusters both in collision problems and in structure problems. After brief explanation of successful applications of AMD to heavy ion collisions and that of the frictional cooling technique for constructing minimum-energy wave functions, the results of the AMD analyses of Li, Be, and B isotopes are discussed. Very good reproduction of magnetic moments is obtained and is explained to be related with the structure-change between cluster structure and shell-model-like structure within each isotope. The superposition of AMD determinants is shown to reproduce neutron halo structure.     

Hadron final states in deep-inelastic leptoproduction on nuclei

We discuss some aspects of the formation of inclusive hadron final states in deep-inelastic electro-, muo- and neutrinoproduction on nuclear targets.The inclusive final states are known to possess a remarkable Q² independence in interactions with free nucleons. Nevertheless, we prove that the nuclear spectra and mean multiplicities should have a rather specific and appreciable dependence on Q². In leptoproduction on heavy nuclei the yields of particles in nucleus fragmentation rise by a factor of two, as at the fixed energy transfer v one passes from incoherent scattering to diffraction scattering, and the total multiplicities change by 20–40%. The effects predicted seem to be detectable with the current and the near-future experimental facilities. Fermilab bubble chamber neutrino experiments and the coming SPS muon and neutrino experiments deserve special attention in this respect. We also comment on the possibilities offered by leptoproduction on nuclei for testing some absorption models.     

Polarization in heavy-ion reactions

A series of experiments is described in which beta-ray asymmetry has been used to determine polarization of heavy-ion reaction products¹²B and the present status of the studies of polarization phenomena in heavy-ion reactions is reviewed. A large amount of angular momentum sustained by the two colliding nuclei gives rise to polarization phenomena of reaction products. Coupling between the degrees of freedom accompanying the intrinsic and the relative motions is investigated from the systematic behaviour of polarization of reaction products disclosed by the experiments.     

Multidimensional Langevin approach to description of near-barrier heavy-ion fusion and deep-inelastic collisions

A six-dimensional Langevin approach is developed for the analysis of near-barrier heavy-ion fusion and deep-inelastic collisions. In its framework, vibrational and rotational degrees of freedom of both nuclei are taken into account explicitly. Calculated fusion cross sections, compound nuclei spin distributions, and angular and energy distributions of deep-inelastic products show satisfactory agreement with experimental data.     

Bremsstrahlung in heavy-ion reactions

We investigate bremsstrahlung processes induced by heavy ions: nuclear dipole and quadrupole radiation, radiation from bound target electrons into the continuum and secondary electron bremsstrahlung (SEB), which contribute to the background of the X-ray spectra. A comparison with experiment is presented.     

A phenomenological model of deep-inelastic collisions between complex nuclei

A simple model of heavy-ion collisions is proposed. Classical equations of motion with inclusion of a phenomenological two-body friction force are integrated numerically along trajectories. The nucleus-nucleus interaction potential which is used in the calculations includes deformation degrees of freedom in the exit channel. Both entrance and exit channel potentials are based on the boundary conditions following the liquid-drop model. The energy-angle distributions of deep-ineIastic reactions are very well reproduced by the model. The existing data on fusion cross sections are compared with the model predictions. This comparison indicates that in the nucleus-nucleus potential a repulsive core is present.     

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.