Equation of State

The current focus of the group is to investigate the Equation of State (EOS) of dense neutron-rich nuclear matter formed in nuclear reactions and which may also exist naturally in compact stars. The explosion mechanism of supernovae, structure and evolution of neutron stars, the emission of gravitational waves from several possible sources, and the dynamics of terrestrial nuclear reactions all depend on the EOS. However, our current knowledge about the EOS of dense neutron-rich matter is still very poor. Its determination has been a common thrust of several operating and/or planned x-ray satellites as well as advanced new radioactive beam facilities being built around the world. Currently funded by the National Science Foundation (NSF) and the Department of Energy (DOE), the group has been developing tools for investigating several critical issues about the EOS of dense neutron-rich matter. The group has productive collaborations with several experimental groups both in the USA and abroad. During the last few years, 6 REU students have collaborated with Prof. Li and his colleagues in addressing some of the most interesting problems in this field leading to 5 publications with REU students as co-authors in top physics and astronomy journals.

Student Projects

Effects of nucleon effective-mass on nuclear reactions in neutron-rich matter

We have several projects appropriate for the REU students to work on during the 10-weeks program each summer. For example, one student can investigate effects of the nucleon effective mass on nuclear reactions induced by radioactive beams using a newly developed transport model. Due to the Pauli blocking in nuclear medium and the finite-range of nuclear interactions, the effective masses of neutrons and protons in dense medium are expected to be different from their values in free space. Moreover, how they may depend on the neutron-richness of the medium is currently a hotly debated question and the answer affects significantly the extraction of nuclear EOS from nuclear reactions.

What You Will Do

Using a transport simulation code developed by Prof. Li and his collaborators, the REU student will study effects of different nucleon effective masses on the temperature and density reached during nuclear reactions as well as the final experimental observables. Comparison with experimental data may allow us to put a constraint on the in-medium nucleon effective mass, its dependence on the neutron-richness of the medium and its effects on the extraction of the nuclear Equation of State. The student will first learn the basic physics of the Boltzmann transport equation in an undergraduate textbook on statistical physics and learn how to use a user-friendly transport model on a Linux computer. Then, the student will learn how to use several mathematical and graphical tools to analyze results of transport model simulations. After reproducing several previous results, the students will learn how to modify a subroutine where the nucleon effective mass is used and the associated physics. Using several values of the nucleon effective mass spanning the current uncertainty range of theoretical model predictions, the REU student will investigate how the variation of the input nucleon effective mass may affect the dynamics and experimental observables of nuclear reactions. By comparing the results of transport model simulations with available experimental data, we expect to put on a constraint on the nucleon effective mass in neutron-rich matter. Using the last 2 weeks of the REU program, the student will sum up his/her studies in a research report which may be turned into a publication in a physics journal.