SHIRIA Work Group
Studies of Heavy-Ion Reactions at RIA

Scientific Program - Overview

Nuclear science studies the behavior of the nucleus as a mesoscopic, quantal multi-body system of nucleons, whose structure and interactions are determined by nucleonic and mesonic degrees of freedom.

Much is known about the low-energy structure of nuclei near the bottom of the beta-stable valley, their interactions, and their decay. Their behavior is dominated by the mean field, a consequence of the synergetic behavior of all nucleons. In this "one-body" domain, nucleus-nucleus interactions are modeled successfully in terms of the response of fast intrinsic (nucleonic) degrees of freedom to slow collective motion. At the opposite, high-energy extreme, nuclei are apparently well represented by ensembles of independent semi-classical nucleons. Here, nucleus-nucleus interactions reflect the superposition of individual nucleon-nucleon scattering ("impulse approximation").

A most interesting, and most challenging, transitional domain of nuclear structure and dynamics has recently become accessible to research at Fermi and intermediate energies, and with exotic nuclei far off stability. Goals of this new research are

• to trace organization and transport of correlated nucleons in nuclear matter evolving from a superconducting Fermi liquid to a viscous hydrodynamical medium and, finally, to a classical gas;
• to describe nuclear structure and dynamics in terms of effective density-, momentum-, and isospin-dependent nucleonic forces and many-body correlations;
• to develop a quantitative theory of nuclear structure and dynamics, as well as applications in terms of phenomenological models of nuclear matter and its response.

Several of these goals of fundamental nuclear science research have already been emphasized in recent Long Range Plans. Success of such an ambitious program has impact beyond fundamental nuclear science. Notably, it would improve understanding of the microscopic quantal many-body problem, of the structure of our macroscopic universe, and of the dynamics of cosmological processes, as they appear right now.

To contribute to these scientific goals, this Working Group plans

• to study transport processes in warm and hot nuclear matter, induced in nuclear reactions by iso-symmetric and iso-asymmetric probes at Fermi and intermediate energies;
• to identify intrinsic and collective degrees of freedom excited in nuclear collisions and nuclear decay
• investigate the coupling between intrinsic and collective motion in terms of effective nucleus-nucleus interactions;
• to establish limits of mechanical (shape) and chemical (consistency) stability of cold, warm, and hot nuclear systems;
• to investigate relations between internal nuclear structure and decay modes of warm and hot nuclei;
• to derive an effective isospin equation of state of nuclear matter.

Specific sections will address individual aspects of this program, as they are developed by the Working Group (see pages linked to above). In particular, the fundamental and practical importance of secondary (RIA) beams of exotic projectiles to the research goals will be discussed.