Coulomb and symmetry-energy effects on proton and neutron density-distributions in central heavy-ion collisions, across beam energies and system masses

¹ Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996, USA
² Department of Physics (Astrophysics), University of Oxford, Oxford OX1 3RH, United Kingdom
³ Facility for Rare Isotope Beams and Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
⁴ Faculty of International Studies, Osaka University of Economics and Law, Osaka 581-8511, Japan

^* e-mail: jirina.stone@physics.ox.ac.uk
^** e-mail: daniel@frib.msu.edu
^*** e-mail: iwata_phys@08.alumni.u-tokyo.ac.jp

Published online: 18 October 2024

Abstract

In this contribution, we review our current and previous investigations of total, proton, and neutron particle number densities and the asymmetry of proton and neutron density distributions achievable in central heavy-ion collisions at beam energy below 800 MeV/nucleon. Furthermore, the effects of the Coulomb interaction and the dependence on a system size in three representative symmetric and asymmetric Ca, Sn and Pb systems are studied. The Boltzmann-Uhlenbeck-Uehling (pBUU) transport and Time-Dependent Hartree-Fock (TDHF) models, employing the SVbas, SkT3 and SVsym Skyrme interactions, are used in these simulations. We find that (i) the highest total densities predicted at E_beam = 800 MeV/nucleon are on the order of ∼ 2.5ρ₀ (ρ₀ = 0.16 fm⁻³), (ii) the proton-neutron asymmetry for maximal densities, δ = (ρ_n^max−ρ_p^max)/(ρ_n^max+ρ_p^max) do not generally exceed the asymmetry in the initial state of the collision at all beam energies and tend to decrease during the reaction, and (iii) a significant portion of this asymmetry has its microscopic origin in Coulomb forces, masking the pure nuclear contribution. In addition, the evolution of normalized maximal proton, neutron, and total nucleon number density with increasing beam energy, the impact of correlations in the reaction, and the time evolution of the proton and neutron density distributions in the plane transverse to the beam direction are illustrated and discussed.