INCOMPRESSIBILITY OF ASYMMETRIC NUCLEAR MATTER

Using an isospin- and momentum-dependent modified Gogny (MDI) interaction, the Skyrme-Hartree-Fock (SHF) approach, and a phenomenological modified Skyrme-like (MSL) model, we have studied the incompressibility K sat (δ) of isospin asymmetric nuclear matter at its saturation density. Our results show that in the expansion of K sat (δ) in powers of isospin asymmetry δ, i.e., K sat (δ) = K0 + K sat ,2δ2 + K sat ,4δ4 + O(δ6), the magnitude of the 4th-order K sat ,4 parameter is generally small. The 2nd-order K sat ,2 parameter thus essentially characterizes the isospin dependence of the incompressibility of asymmetric nuclear matter at saturation density. Furthermore, the K sat ,2 can be expressed as [Formula: see text] in terms of the slope parameter L and the curvature parameter K sym of the symmetry energy and the third-order derivative parameter J0 of the energy of symmetric nuclear matter at saturation density, and we find the higher order J0 contribution to K sat ,2 generally cannot be neglected. Also, we have found a linear correlation between K sym and L as well as between J0/K0 and K0. Using these correlations together with the empirical constraints on K0 and L, the nuclear symmetry energy E sym (ρ0) at normal nuclear density, and the nucleon effective mass, we have obtained an estimated value of K sat ,2 = -370 ± 120 MeV for the 2nd-order parameter in the isospin asymmetry expansion of the incompressibility of asymmetric nuclear matter at its saturation density.

EOS OF NUCLEAR MATTER WITHIN A GENERALISED NJL MODEL

We derive the equation of state (EOS) of nuclear matter within a generalised Nambu–Jona–Lasinio (NJL) model which saturates at normal nuclear density, ρ0. Chiral symmetry is restored at ~ 6–7 ρ0. At low densities the model includes clustering and reproduces the properties of nuclear matter namely binding energy and incompressibility. At high densities (ρ>3–4.5 ρ0) quark matter is more stable than nuclear matter. The confinement-deconfinement phase transition is studied.

HYPERONS IN HIGH-DENSITY NUCLEAR MEDIUM: IS Λ-Σ0 MIXING LARGE OR SMALL?

The Λ-Σ0 mixing in neutron star matter is discussed in three theoretical models: the G-matrix theory, the relativistic mean field theory and the QCD sum-rule approach. The mixing of 2~8% at the critical baryon density of Λ appearance(2.3 times of the normal nuclear density) is predicted in the G-matrix theory. The second and third models give smaller mixing, 0.2~1.0% and < 0.25%, respectively. Since the G-matrix theory is the most dynamical model among the three, the mixing of 2~10% at 2~3 times of the normal density may be realistic.

Quelques aspects de la physique des collisions noyau–noyau à énergie ultra relativiste

We discuss the results of the measurements of the energy flow and multiplicity for the collisions of 16O and 32S with a set of target nuclei at an incident energy of 60 and 200 GeV/nucleon and 200 GeV/nucleon, respectively. These measurements have been performed at the European Organization for Nuclear Research (CERN) super proton synchroton by NA-34/HELIOS (high energy lepton and ion spectrometer), NA-35, NA-36, NA-38, and WA-80 in various pseudorapidity regions. The measurements of the transverse energy (ET) distributions provide an understanding of the concept of the stopping power and the estimates of the energy density reached. The energy densities reached in these collisions (~ 5 GeV/fm3) are at least an order of magnitude larger than the normal nuclear density (0.15 GeV/fm3) and are also in the region of the critical value of ~ 2.5 GeV/fm3 obtained from lattice gauge theory. [Formula: see text], obtained by combining the transverse energy and the multiplicity measurements, is compared with earlier results reported in cosmic-ray studies. The pT spectra of the charged particles and photons produced in these collisions are compared with the corresponding spectra measured in proton–nucleus collisions. The present situation suggests the study of new observables.

SIX-QUARK CLUSTERS IN NUCLEAR MATTER AT LOW TEMPERATURES

The two-phase system consisting of nucleons and six-quark clusters is investigated. The interaction between nucleons and six-quarks is represented by a sum of the Fermi and Yukawa potentials. The temperature behavior of nucleon and six-quark concentrations versus density is found. It is shown that with a normal nuclear density, six-quark clusters may amount to about 10%, which is in agreement with experiment.

A flux-tube model of hadrons in nuclear matter

A flux-tube model of hadrons is used to study the modification of hadronic properties in nuclear matter. It is shown that nuclear binding and the EMC effect are consequences of partial deconfinement, and that complete deconfinement occurs at about six times normal nuclear density. It is predicted that nucleon resonances are much more strongly bound than the nucleon, and that there is a maximum l beyond which nucleon resonances do not exist in nuclear matter.