Rutgers University Department of Physics and Astronomy

2000-01 Handbook for Physics and Astronomy Graduate Students

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Research Programs

Theoretical Nuclear Physics

Nuclei are interesting many-body systems. One can try to explain their properties either in the "classical" way, in terms of interacting neutrons and protons, or, more fundamentally, in terms of their quark substructure. Their properties can be determined experimentally using various probes, such as intermediate energy electrons, protons, and pi-mesons. To extract nuclear properties from the experiments, however, one must have reliable theories for the scattering processes involved.

Nuclei can also be used to test certain aspects of elementary particle theory. For example, the nature of the neutrino can be studied via the double beta decay of certain nuclei. Another example involves heavy ion collisions at high energies. When two relativistic nuclei collide, nuclear matter at very high temperatures and density can be produced, possibly resulting in new forms of matter such as quark-gluon plasmas or a condensate of pi-mesons.

Professor David Harrington

Positive K-mesons are the most weakly interacting of the strongly interacting particles. There is a still unexplained discrepancy between experiment and theory, however, for their interaction with nuclei. One possible explanation involves meson exchange currents. I am trying to check some of the assumptions that go into the calculation of these contributions by looking at their effects in large-angle scattering from deuterons where they may dominate other contributions to the cross section. I am also trying to see if accurate measurements of the total cross sections for scattering of high-energy nucleons and pions from a range of heavy nuclei can be used to distinguish among different models describing the composite nature of these particles. With certain approximations each of these models corresponds to a prescription for a cross-section distribution function which specifies the probability that the particle is in a configuration which will interact with a nucleon with a given total cross section. Fluctuations between states of different cross sections decrease the total cross sections on heavy nuclei by an amount depending on the model used.

Professor Willem Kloet

I am studying the transition region between nucleon degrees of freedom and quark degrees of freedom. From very high energy experiments we know that nucleons have a substructure of quarks and gluons. It remains an open question how processes in the transition region should be modeled. As an example, I study the annihilation of nucleons and antinucleons into mesons. In this very short range process, models based on nucleon degrees of freedom fail. By building models for the annihilation process using other degrees of freedom, one can get insight in the substructure of the nucleon for relatively low energy processes.

Professor Aram Mekjian

My research is concerned with understanding the collision between two heavy ions of high energies. By looking at these collisions, we are trying to find new phenomena that may occur when nuclei are compressed to high densities. These phenomena include the production of quark matter, pion condensation, and the appearance of a density isomer or Lee-Wick matter. Using statistical mechanics and thermodynamics, the distribution of products in relativistic heavy ion collisions has been studied. The formation of composite nuclei has been formulated in the same framework that accounts for the formation of the elements under explosive conditions as in supernovae explosions and in the big bang.

Professor Larry Zamick

My current research concerns the effects of higher shell admixtures on properties of nuclei. Topics which are addressed when realistic interactions are used include "self weakening of the tensor interaction in a nucleus due to higher shell admixtures" and the effects of intruder states in 8Be and 8B on reactions of importance for the production of elements in the stars, e.g. p + 7Be -> 8B + [[gamma]] (note that 8B is the main producer of high energy neutrinos in the sun). In order to better understand nuclear collectivity we also use the schematic quadrupole-quadrupole Q*Q interaction. We show a new way to get Elliott's SU(3) results without invoking a momentum dependent part to the quadrupole operator. In this new formulation SU(3) symmetry is restored by including the particle-core interaction.

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Revised November, 2000