Research in Nuclear Physics enables us to study quantum mechanical systems of strongly interacting particles. Although it originally appeared that the nuclear forces were quite different from those of electricity and magnetism, it is now believed that they are all described by the same basic kinds of fields and gauge interactions. As a result, the field of Nuclear Physics has expanded beyond the initial focus on nuclear structure and dynamics to be concerned with the application of gauge theories of nuclear forces to strongly-interacting systems at all length scales, particularly at scales where the quark and gluon sub-structure of the nucleus and its constituents is revealed. Experiments are being carried out which explore the way in which quarks and gluons are confined within the physical particles in which they are bound, nucleons and mesons. Another important impact that the Standard Model of strong and electroweak interactions has had on nuclear physics is that it allows certain properties of nucleons and nuclei to be calculated very precisely. Theoretical investigations are being carried out which enable these precision measurements to be interpreted in terms of the Standard Model and its extensions. The nuclear physics program at UConn also has important interdisciplinary features, addressing pivotal questions in Nuclear Astrophysics on the interface of Nuclear Physics with Astrophysics and Space Science, as well as applications to Nuclear Medicine and Materials Science.
We are participating in a number of experiments to study key nuclear reactions that take place in stellar nuclear burning. We concentrate on precision measurements that address the most important outstanding questions of nuclear astrophysics. We are presently involved in several experiments probing the standard solar model through the study of the fusion of Beryllium-7 with a proton to form Boron-8 and its subsequent beta-decay and neutrino emission -- ``the key uncertainty in the solar neutrino problem''. These experiments take place at state-of-the-art radioactive beam facilities at Louvain-La-Neuve in Belgium, RIKEN near Tokyo in Japan, and GSI near Frankfurt in Germany. In Belgium we study the direct reaction with a Be-7 beam while in Japan and Germany we study the inverse reaction through the Coulomb Dissociation of B-8. In addition we plan to produce radioactive Be-7 targets for use with a low energy proton accelerator in the United States. Our second area of concentration involves studies of Oxygen formation during stellar Helium burning. This reaction determines the ratio of Carbon to Oxygen at the end of this phase of stellar evolution, which in turn determines the final fate of massive stars, neutron stars or black holes. We are involved in experiments with a photon beam at TUNL in North Carolina and with a new experiment with an electron beam at Bates lab in Massachusetts. In both experiments we study the inverse reaction through the break up Oxygen-16 into Carbon-12 and Helium-4. In addition we regularly use the tandem accelerator at Yale to test our experimental designs. In addition we carry out research at numerous other facilities throughout the US including Argonne National Lab, Oak Ridge National Lab, and the National Cyclotron Facility at Michigan State University.
In addition to our astrophysics experiments we are participating in several additional studies in applied low-energy nuclear physics. We are studying the commercial and security uses of neutrons and x-rays from compact fusion reactors; the possible production of fusion neutrons in sonoluminescence, a little-understood process, whereby a standing sound wave creates a bubble in a liquid which periodically collapses emitting light; and the development of novel materials for the production of radioisotopes to be used in both our astrophysical and biomedical applications.
Research in nuclear theory at the University of Connecticut seeks both to understand the nucleus as a strongly-interacting many-body system and to use the nucleus as a ``laboratory'' for the study of fundamental interactions. Of particular interest are nuclear processes which violate fundamental symmetries, such as parity-invariance and time-reversal invariance. Such symmetry-violating processes offer unique opportunities to reveal signatures of physics lying outside the Standard Model of electroweak interactions. At present, a special emphasis at UConn is being put on the theoretical interpretation of parity-violating effects in electron scattering from nuclear targets, as recent advances in polarized beam technology have now made high-precision measurements of these effects feasible. These studies reach across traditional boundaries, including parity- and/or time-reversal violating effects in atomic systems as well. The insight achieved from such investigations complements what one learns from very high-energy processes and has important consequences for our understanding of the basic forces of nature.
Considered as a many-body system, the nucleus presents theorists with the challenge of understanding the strong interaction in a regime where traditional perturbation theory breaks down. Theoretical work is being carried out at UConn to understand both the strong interaction between the quarks and gluons inside the nucleon, and the strong interactions between the nucleons inside the nucleus. These studies are presently focusing on the role played by ``sea quarks'' in the structure of the nucleon, and on the force experienced by a nucleon as it is ejected from a nucleus hit by an electron. The sea-quark structure of the nucleon is being studied experimentally with parity-violating electron scattering. The theory staff at UConn is taking a leading role in developing the framework for understanding these measurements and their implications for our conceptual picture of the nucleon. The analysis of the final state nucleon-nucleus interaction is needed in order to understand electron scattering experiments aimed at elucidating the correlations between nucleons in the nuclear ground state. An example of such an experiment is the emission of a nucleon from a nucleus by an energetic incident electron. Current research at UConn seeks to apply computational techniques developed from the nucleon knockout problem to a variety of processes in atomic and molecular physics as well.
With the establishment of quantum chromodynamics as the correct theory of strong interactions at small scales, a field of study has opened up on the boundary between nuclear and high-energy physics. Known as intermediate energy physics, it seeks to understand how the world of quarks and gluons at small scales gives rise to the observed spectrum and structure of mesons and baryons at the nuclear length scale. The Thomas Jefferson Laboratory in Virginia was constructed during the 90's for the purposes of this physics program. Faculty and students in our group are actively pursuing experiments at Jefferson Lab.
In one experiment called Radphi, researchers are hunting for certain rare reactions which will yield important clues about the internal structure of two mesons known as the f0 and a0. If it turns out, as expected according to some models, that these two mesons are composed of more than one quark-pair (in mesons quarks always come in pairs) then this will be the first real evidence for such an exotic particle. A whole host of these exotic mesons is expected to exist based upon QCD, but evidence for their existence has only begun to accumulate over the last five years. This research group is also involved in planning more ambitious experiments to mount a systematic search for these elusive mesons. These plans are for future work at a facility at Thomas Jefferson Laboratory called Hall D. The discovery of the existence of a multiplet of exotic mesons will provide a fruitful testing ground for models which provide a conceptual framework for understanding how quarks are confined inside hadrons.
Most reactions involving strongly-interacting particles depend on these particles' internal structure, the study of which is the main subject of intermediate energy physics. There are some processes, however, which have been shown to be independent of the details of hadron structure and depend principally on the properties of the bare quarks inside. Such is the case for experiments which measure the asymmetry in the scattering of polarized electrons from a proton target, comparing right-handed and left-handed electrons. The value for this asymmetry is predicted precisely by the Standard Model of electroweak interactions. A measured deviation of this quantity from the Standard Model value would indicate the existence of new particles which have not yet been observed directly in high-energy experiments. Our group is involved in planning for an experiment of this kind, to be carried out at Jefferson Lab.
Students working in our group spend part of their time working at Jefferson Lab. There they gain experience working on collaborative projects, gain exposure to an international community of researchers, and take advantage of the educational environment of a national lab for their professional development.
Applications of Nuclear Physics techniques to Nuclear Medicine as well as to Astronomy and forensic studies are under development. Some of these studies are in collaboration with the Jet Process Corporation in New Haven, CT, where we utilize new materials for the efficient production of unstable isotopes. We are also developing new scintillating materials for applications in gamma-ray measurements in space.
Other applications of Nuclear Physics include work conducted in the U.S. and in Germany to develop a resonant reaction analysis for understanding chemical kinetics, as well as an advanced combined x-ray, gamma-ray and neutron detector for NASA to use on landers and rovers. This detector is needed for the identification of particles from cosmic ray interactions for the purpose of obtaining a better understanding of the formation and evolution of our solar system. In addition, we are studying solar activity to investigate x-ray production in the sun. The properties of rare earth oxyorthosilicates are also being studied to facilitate improving the capabilities of gamma-ray detectors currently used for advanced PET medical imaging instruments.
New numerical methods for solving coupled Schrödinger equations are being developed by faculty in the nuclear physics group, together with faculty in the Mathematics Department. These methods are also currently being applied to the study of collisions between ``ultracold'' atoms -- a fact that illustrates the usefulness of interdisciplinary collaboration.