Showing papers on "Nuclear matter published in 1979"

Variations on a theme of nuclear matter

Abstract: The authors review new techniques developed to apply the variational method to the nuclear matter problem. The variational wave function is taken to be ($S{\ensuremath{\Pi}}_{ilj}{\mathrm{F}}_{\mathrm{ij}}$) $\ensuremath{\Phi}$; the correlation operators ${\mathrm{F}}_{\mathrm{ij}}$ can in principle induce central, backflow, spin isospin, tensor, etc. correlations, and $\ensuremath{\Phi}$ is the ideal Fermi gas wave function. The application of diagrammatic cluster expansion and chain summation techniques to calculate expectation values with such wave functions is discussed in detail. The authors also give a brief overview of various other approaches to the calculation of the binding energies of quantum fluids, and a comparison of results for simple systems such ad helium liquids. Results obtained by various methods for simplified models of nuclear matter, which include central, spin, isospin, and tensor forces, have converged significantly in recent months. Results obtained with more realistic models which include the spin-orbit potentials are also discussed. The potential models considered so far either give too little binding or too high equilibrium density.

Evidence for a Blast Wave from Compressed Nuclear Matter

Abstract: Central collisions of heavy nuclei at c.m. kinetic energies of a few hundred MeV per nucleon produce fireballs of hot, dense nuclear matter. Each fireball explodes, producing a blast wave of nucleons and pions. Several features of the observed cross sections for pions and protons from Ne on Na F at 0.8 GeV/nucleon (lab) are explained by the blast wave, but contradict earlier, purely thermal models. The available energy is equally divided between translational energy of the blast, and thermal motion of the particles in the exploding matter.

Axial Currents in Nuclei: The Gamow-Teller Matrix Element

Abstract: We propose that the quenching of Gamow-Teller matrix elements in light nuclei can be effectively described by a mechanism that governs the $p$-wave pion-nucleus scattering. This may be providing a solution to the long-standing problem. The resulting Landau-Migdal parameter ${g}^{\ensuremath{'}}$ turns out to be quite consistent with the values extracted from the spectra of pionlike excitations and places a stringent constraint on pion condensation in nuclear matter.

Evidence for a Soft Nuclear-Matter Equation of State

Abstract: The entropy of the fireball formed in central collisions of heavy nuclei at center-of-mass kinetic energies of a few hundred MeV per nucleon is estimated from the ratio of deuterons to protons at large transverse momentum. The observed paucity of deuterons suggests that strong attractive forces are present in hot, dense nuclear matter, or that degrees of freedom beyond the nucleon and pion may already be realized at an excitation energy of 100 MeV per baryon.

Confinement of quarks in nuclear matter

Abstract: The transition from low density nuclear matter to high density quark matter can, it is argued, take place in two steps: first, a percolation transition at (subnuclear densities, if the radius of the nucleon is ⪅1 fm) in which the quarks become deconfined but still remain localized, followed by an unbinding transition at higher density, in which the matter becomes a uniform quark Fermi liquid.

Effective Interaction with Three-Body Effects

Abstract: Three-body effects, which are effects of three-body force and three-hotly correlation, are introduced into the two-body nuclear force in a semi-phenomenological way to reproduce the nuclear saturation over all nuclei by the lowest order Brueckner theory. On the hasis of the reaction matrix calculation of nuclear matter with this two-body force including the three· body effects, a new effective potential is proposed which includes two independent parameters, namely, nuclear density and starting-energy. Because of the effect of three-body force, this effective potential is more attractive in the 'E state, compared with the usual one, and assures overall saturation without any artificial modification. The starting-energy dependence of the effective potential is also strengthened by the three- body force. The starting-energy dependence is found to work well for nuclear saturation together with the density dependence. Present density dependence is weaker than that of the usual clensity dependent effective potentials. The effective potential is decomposed into central, spin-orbit and tensor components.

Microscopic optical potentials

Abstract: Various versions of infinite nuclear matter reaction matrix elements (t‐matrix elements) were generated from free NN potentials. Most emphasis is put on calculations with the momentum dependent Paris potential as input. Thereupon is parametrized a complex energy and density dependent interaction (25‐500 MeV) with convenient Yukawa‐form factors to serve as effective interaction. It is the driving two‐body transition operator in applications to finite nuclei using a local density approximation. Studies concentrate on elastic channel microscopic optical model potential and its general structure as compared to phenomenological potentials. Further detailed checks on our effective interactions were performed with exemplary studies of (p,p′) transitions.

LOCV calculations with a self-consistent treatment of isobars

Abstract: The results of a series of lowest-order constrained variational calculations for various nucleon fluids are presented. The calculations are based upon the Reid soft-core potential (1968) and allow in a self-consistent fashion for the explicit excitation of a nucleon into an N*(1234) state via a recent transition potential proposed by Green, Niskanen and Sainio (1978). For nuclear matter a binding energy of 16 MeV per nucleon is obtained at a saturation density 0.25 N fm-3. The compressibility of nuclear matter is calculated to be 300 MeV. From a study of asymmetric matter a symmetry coefficient of 33 MeV is obtained. It is found that the inclusion of N*'s in beta-stable matter leads to a suppression of the proton abundance at high densities.

LOCV calculations and the three-body cluster energy in nuclear matter

Abstract: Two-body correlation functions obtained in a LOCV calculation on nuclear matter using the Reid soft-core potential are state averaged and then used to calculate the three-body convergence parameter kappa 3 and three-body cluster energy E3. kappa 3 is found to be less than 0.1 for Fermi momenta kF

From heavy-ion elastic scattering to fission: A unified potential for the description of large-scale nuclear collective motion

Abstract: In a generalization of the modified liquid-drop model obtained by requiring that two semi-infinite slabs of constant-density nuclear matter have minimum energy at zero separation, we calculate the generalized nuclear surface energy by means of a double volume integral of a Yakawa-plus-exponential folding function. This leads to a unified nuclear potential that is useful for describing heavy-ion elastic scattering and fusion, nuclear fission, and nuclear ground-state masses and deformations.

Three-dimensional calculations on the formation of density isomers in high energy heavy ion collisions

Abstract: A three dimensional fluid dynamical model is used to investigate the possibility of forming superdense abnormal nuclear matter (“density isomers”) in fast collisions of heavy nuclei, the dependence of the formation process on the bombarding energy and on the impact parameter An experiment for the detection of such phase transitions in nuclear matter is suggested

Quark Confinement in Unusual Environments

Abstract: We consider the properties of one-dimensional gauge field theories at finite temperatures and densities. The massive Schwinger model in the presence of a uniform charge background is shown to form a Wigner crystal which Debye screens charged impurities. The two-species Schwinger model with oppositely charged fermions is studied at finite baryon density. This system does not undergo a phase transition as the density is increased, but becomes progressively more polarizable until at infinite density Debye screening occurs. Finally we consider the massive Schwinger model at nonzero temperature and show that Debye screening occurs at infinite temperature. We speculate that in three dimensions this last transition occurs at finite temperature.