L. Wilets

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

Abstract 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 p ij r ij ≧ξ h , 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.

Theory of kaonic atoms

Abstract A nonlocal energy-dependent self-consistent kaon-nucleus optical potential is derived for kaonic atoms. Energy level shifts and widths are calculated for several light nuclei, and the results are compared with experiment. The sensitivity of the results to changes in parameters of the nuclear matter distribution is studied. Nonlocality and off-energy-shell effects are examined. The optical potential is derived by means of a Brueckner-type many-body theory with the independent pair approximation for the kaon and the nucleon. The two-body interaction on which the optical potential depends is represented by separable potentials of the Yamaguchi form. Coupled channels ( K N and Σπ) are used for the I = 0 states, which are dominated by the Y 0 ∗ resonance, and only a single channel ( K N ) is used for the I = 1 state. Calculations are carried out in three levels of approximation of the nonlocal energy-dependent optical potential. In no approximation is the potential found to be proportional to the nuclear density. Indeed, the real part of the potential changes sign in the nuclear surface. Sensitivity of the results to variations in the nuclear matter distribution is investigated and found to be on the order of experimental error. Nonlocality and off-energy-shell effects are estimated to be at least as large as this error, so that these effects must be included if one wishes to extract information about the nuclear surface from the existing experimental data. The use of correct nucleon wavefunctions and binding energies is similarly found to be essential in the calculation.

ATOMIC PARITY NONCONSERVATION: ELECTROWEAK PARAMETERS AND NUCLEAR STRUCTURE

There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic-structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the standard model at the level of one-loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and nonrelativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear-structure effects may preclude using Pb isotope ratios to test the standard model at better than a 1% level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei.

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

Abstract 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.

Dynamics and non-adiabaticity in the fission process☆

Abstract The fission process takes a time which is not appreciably longer than single-particle times. Therefore it is not clear that the fragmentation process can be described in an adiabatic limit. In this paper the excitation of the nucleus during the deformation process is calculated both analytically and numerically within the framework of the cranking model. The model nucleus is defined by a Hamiltonian containing a deforming Nilsson-type single-particle Hamiltonian, pairing interaction, and a schematic residual interaction. For this time-dependent Hamiltonian, the time-dependent Schrodinger equation is solved by (i) perturbation expansion for the analytic discussion and (ii) direct numerical procedure. For the numerical solution, the Hilbert space is confined to the BCS ground state and a limited number of two quasi-particle excitations corresponding to lowest excitation energy. Calculations have been performed for a vibrating calcium and a fissioning uranium nucleus.

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

Abstract 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.

Exact solutions to the Schrödinger equation for potentials with Coulomb and harmonic oscillator terms

Abstract Exact solutions to the Schrodinger equation for potentials containing Coulomb (∼1/ r ) plus harmonic oscillator (∼ r 2 ) terms are found, subject to constraints on the ratio of the strengths of the Coulomb and harmonic oscillator terms. The solutions have the simple form of a product of exponential and polynomial functions.

Semiclassical description of antiproton capture on atomic helium

A semiclassical, many-body atomic model incorporating a momentum-dependent Heisenberg core to stabilize atomic electrons is used to study antiproton capture on helium. Details of the antiproton collisions leading to eventual capture are presented, including the energy and angular-momentum states of incident antiprotons which result in capture via single- or double-electron ionization, i.e., into He[sup 2+][ital [bar p]] or He[sup +][ital [bar p]], and the distribution of energy and angular-momentum states following the Auger cascade. These final states are discussed in light of recently reported anomalously long-lived antiproton states observed in liquid He [Iwasaki [ital et] [ital al]., Phys. Rev. Lett. 67, 1246 (1991)].

THE CHROMO-DIELECTRIC MODEL: CONFINEMENT, EFFECTIVE COUPLING AND CHIRAL INVARIANCE

Abstract The chromo-dielectric mechanism of absolute confinement is studied in the nontopological soliton model. The model lagrangian is chirally invariant, since it contains no direct coupling between the quarks and the scalar field. The static chromo-electric gluon propagator is calculated in medium in the one-loop approximation, and the ultraviolet divergence in the self-energy of fixed quarks is regulated by a form factor. Effective quark-scalar coupling emerges through the self-energy of the quarks in the dielectric medium, which is a function of the scalar field.

Confinement, chiral symmetry breaking, and the pion in a chromo-dielectric model of quantum chromodynamics

Abstract We study a chirally symmetric effective model of quantum chromodynamics, where the long-range parts of the (non-abelian) gluon self-interactions are assumed to give rise to a color-dielectric field. In particular we show how in this model confinement and the Goldstone pion arise naturally and simultaneously from dynamical chiral symmetry breaking. We also provide justification for successful chiral bag models, including for example the cloudy bag model.