Theoretical Nuclear Physics

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Many exciting advances and discoveries are being continually made in nuclear physics. With the development of rare isotope beam facilities, phenomena associated with the proton-neutron asymmetry in nuclear matter, essential for understanding the properties of neutron stars and the stellar processes that are responsible for the synthesis of elements, can now be studied over a much broader range than hitherto possible. For collisions of nuclei at ultrarelativistic energies available from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, experimental observations are consistent with the creation of a new phase of matter, the quark-gluon plasma, that consists of the constituent quarks and gluons inside protons and neutrons and is believed to have existed during the first microsecond after the Big Bang. In this project, we will continue to develop transport models for heavy ion collisions at various energies and with both stable and rare isotopes and to carry out systematic comparisons of theoretical predictions with experimental data. For collisions involving rare isotopes of large neutron or proton excess, we shall extend the isospin-dependent transport model, which includes different dynamics for protons and neutrons, to include also the dynamics of light nuclei and the medium effects on produced pions. We will then use this model to study the dependence of the energy of nuclear matter on its density and proton to neutron asymmetry via the two-nucleon correlation functions, light nuclei production, the relative diffusion between protons and neutrons, and the ratio of charged pions. For ultra-relativistic heavy ion collisions, we will refine the multiphase transport model, which includes both the dynamics of quarks and gluons and that of ordinary hadrons as well as the transition between these two phases of matter, by using the quasi-particle picture to describe the initial partonic matter and including the effect of strong color fields on the parton dynamics. The model will then be used to study the properties of the quark-gluon plasma through the spectra of produced photons, dileptons, and particles that consist of heavy strange and charm quarks, the energy loss of very energetic particles produced from initial hard collisions, the charge-dependent correlations, and the event-by-event fluctuations of produced particles. With the knowledge acquired from these studies about nuclear matter and the quark-gluon plasma, we will further investigate the structure of finite nuclei and the properties of neutron stars. The proposed project has the intellectual merit of not only impacting directly the research programs at existing radioactive beam accelerators and the future Facility for Rare Isotope Beams (FRIB) as well as at RHIC and the Large Hadron Collider (LHC) but also contributing to the understanding of many important issues in astro- and particle physics. It also has the broader impact of providing participating young students and postdoctoral researchers a broad research experience that would prepare them well for careers in either nuclear science or other areas to continue their contributions to the scientific and technological advance in our society.