First-Principle Nuclear Structure and Reactions for Astrophysics and Experiments with Rare Isotope Beams

Louisiana State University, Baton Rouge LA

Investigators

Abstract

Following the history-making discovery of nuclear fission, which manifested the huge amount of energy that is released by breaking the strong bonds between neutrons and protons, nuclear physicists have searched for ever more comprehensive explanations of the properties of the atomic nucleus. Such advances are critical to predict exotic nuclei in processes under extreme conditions as stellar mergers and explosions, and to probe neutrino-related processes. The recent advent of radioactive beam facilities has enabled exotic-nuclei measurements, based on collisions of nuclei and their reactions. To predict inaccessible nuclei, these reactions must be well understood and modeled. However, exact solutions exist up to about five particles. The objective of this program is to expand dramatically the capabilities of nuclear reaction theory, by providing input to reaction simulations that is anchored in first principles but also can accommodate heavier nuclei and enhanced deformation. This is important for studies of the origin of elements, one of the biggest challenges in physics today, and has a wider impact since nuclear energy applications and national security research have similar needs. Future leaders (postdoc and students) are trained in low-energy nuclear science and petascale computing, while advancing a web-database for research and educational purposes. The overarching goal is to learn from and inform experiments at radioactive beam facilities, and to predict properties of experimentally inaccessible nuclei that are key to advancing our knowledge about astrophysical processes. The program focuses on improving reaction modeling by constructing the effective interaction between a target and a projectile from first principles (historically, referred to as an optical potential and fitted to experimental data), which now account for the challenging microscopic structure of the participating nuclei. As these interactions are an essential input to numerous reaction models that are currently in use, the new developments serve as an important tool in a broad spectrum of studies. The project capitalizes on a symmetry-guided approach that, by exploiting symmetries known to dominate the dynamics, has enabled ab initio investigations of heavier nuclear species, deformed or not. In this approach, all participating particles are treated on the same footing within a "shell model" picture, while employing chiral effective field theory interactions between protons and neutrons. The end products include calculations of beta decays in nuclei of enhanced deformation, and of reaction observables, e.g., cross sections for scattering, charge-exchange, and (d,p) reactions, of importance to astrophysics. This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.