Current Research

Motivation

Nuclear physics and symmetries have a rich history of interconnections. Much emphasis has been placed on the study of symmetries, both fundamental and approximate -- parity, time reversal invariance, isospin. The primary interest is the manifestation of the symmetry in the nucleus and how the symmetry is affected by the many body system.

In the work by the TRIPLE collaboration, parity nonconservation (PNC) is studied in the neutron-nucleus interaction in medium and heavy nuclei. The prospect of placing additional constraints on the pi and rho PNC mesonic coupling constants is of course of interest, especially given the apparent lack of neutral current enhancement of the isovector pi coupling. What is new and of general interest is the effect of the many body system on PNC. The most striking feature is that the magnitude of some PNC observables is enhanced by as much as 10⁶ relative to the nucleon-nucleon value. the origin of this enhancement and the key to the analysis lies in studying the compound nuclear system. The PNC matrix elements are assumed to be random variables, and generic features such as the magnitude and mass dependence of the effective nucleon-nucleus interaction are studied statistically. Measurements performed at TUNL by our group are extending these studies to lower masses using charged particle resonances.

The effects of the many body system on a well understood approximate symmetry -- isospin -- also provide an excellent test of for many body effects on broken symmetries. Using complex nuclear systems as a laboratory for the study of broken symmetries naturally leads to an interest in the statistical laws which govern this system. The standard theory that describes fluctuations is Random Matrix Theory (RMT). Just as the complex system has a striking effect on the symmetries and on symmetry-breaking, the converse is true: The statistical distributions that characterize the fluctuation properties of the complex nuclear system reflect the underlying symmetries. In fact, one can study the statistical distributions of eigenvalues and of transition strengths to search for the effects of symmetries, and even detect hidden symmetries. Our measurements on isospin symmetry breaking in ²⁶Al provided the first experimental test of the effects of symmetry breaking on the fluctuation properties of eigenvalues and transition strengths. The eigenvalue distributions agree with predictions of RMT, but there is no theoretical prediction for the effects on the transition strengths. We are now performing similar studies on the neighboring nuclei ³⁰P and ³⁴Cl .

Thus our efforts involve the examination of the effects of the complex many body nuclear system on symmetries and, conversely, study of the effects of the symmetries on the many body system.

Current Projects

Excitation function measurement of the ⁵²Cr(p,p) and ⁵²Cr(p,p') reactions (Lance McLean)

[no abstract available]

Excitation function measurement of the ⁵⁰Cr(p,p) and ⁵⁰Cr(p,p') reactions (Bill Beal)

[no abstract available]

Parity violation in neutron resonances (Dr. Gary Mitchell)

[no abstract available]