Nuclear Physics Research
A. M. Nathan,* R. J. Holt,* D. H. Beck, P. T. Debevec, D. W. Hertzog, N. C. R. Makins, S. E. Williamson, M. Bouwhuis, T.-H. Chang, Z. Lu, C. J. G. Onderwater, K. Wijesooriya, P. Bailey, B. Bains, R. Cadman, J. Grames, F. Gray, R. Hasty, B. Owen, C. Polly, M. Roedelbronn, E. Schulte, M. Sossong
National Science Foundation, PHY 94-20787

The group doing experiment nuclear physics at Illinois pursues its studies at a variety of accelerator facilities through the world, using high-energy beams of electrons, photons, muons, and antiprotons. Nuclear Physics Studies Using Beams of Photons at Jefferson Laboratory A series of experiments are being undertaken that are aimed at obtaining an understanding of the meson exchange/quark nature of the nucleon and few-nucleon systems. The Illinois group is leading this effort at Jefferson Laboratory. These experiments include deuteron photodisintegration, pion photoproduction from nucleons and light nuclei, and Compton scattering from the nucleon. The later experiment is led by Illinois and involves the construction of a calorimeter for detection of high-energy photons. Nuclear Physics Studies Using Beams of Electrons There are two programs in which we are heavily involved. First is a program to measure the contribution of strange quarks to the vector current of the nucleon. These experiments utilize the parity-nonconserving interference between electromagnetic and weak neutral currents in the scattering of longitudinally polarized electrons from the proton. One of these experiments, called SAMPLE, has measured the strange quark contribution to the magnetic moment of the proton with data taken at the MIT/Bates Linear Accelerator. A far more ambitious program is the G0 experiment, which will take place at the new national electron facility, Jefferson Laboratory. The entire effort involves a large international collaboration led by the Illinois group. Among other things, our group is responsible for the construction of the key piece of instrumentation that makes the experiment possible, a novel superconducting magnetic spectrometer. Second is a series of experiments (HERMES), which will measure the spin structure of the proton and neutron by scattering longitudinally polarized electrons from polarized protons and neutrons. This will allow us to determine how much each type of quark contributes to the spin of the nucleon. An exciting new initiative is an experiment to measure the contribution of the gluons to the spin of the proton. This involves upgrading the HERMES experiment to detect 'charmed' mesons, an effort in which the Illinois group plays a major role. The experiments are underway at the DESY facility in Hamburg, Germany. Study of the Nuclear Three-Body Force at Indiana University Cyclotron Facility Members of the group have designed and constructed a laser-driven polarized hydrogen and deuterium source for use as an internal target at a circulating beam facility. The target was taken to cooler ring at Indiana University and an experiment was done to study the spin structure of the deuteron by scattering polarized protons from the polarized deuterium target. In the process, the first definitive evidence was found for a dynamical three-body force in nuclei. A follow-up experiment is planned to study further the nature of the three-body force. Atomic Parity Violation and Metastable Hydrogen/Deuterium Beam As a follow-up both to our work developing laser-driven polarized hydrogen/deuterium targets, our interest in parity-violating electron scattering, and our interest in studying tests of the Standard Model, we have initiated a program to develop a high-intensity thermal, metastable hydrogen beam. The primary goal is to study parity violation in atomic hydrogen in order to place stringent constraints on physics beyond the Standard Model. Precision Measurement of the Anomalous Magnetic Moment of the Muon Measurements of the magnetic dipole moments of particles have played an important role in understanding the structure of matter. Deviations from the expected characteristics of 'point-like' particles appear as so-called anomalous moments and are sensed by observation of the precession rates of such particles in magnetic fields. For protons and neutrons, anomalous magnetic moments are big, as expected for these particles, which are each built from three quarks. But for electrons and muons the anomaly is tiny, and so far is in agreement with theoretical expectations to an extraordinary degree of precision. We are participating in a new experimental effort to measure the muon anomalous magnetic moment 20 times better than previous work; this will result in a test of the relevant quantity termed '(g-2)' to a level of 0.35 ppm. If achieved, the result will test the contributions of the weak interaction to the muon (g-2) factor-an essential component of the electroweak theory, which has not yet been detected experimentally. Deviations from the theory may occur only by invoking new physics phenomena. The experiment is being mounted at the Brookhaven National Laboratory. Our Illinois group has built the major detectors, constructed novel electronics simulation systems, and developed a unique electron traceback system from state-of-the-art particle-tracking devices. In addition, we are spearheading the 'Midwest analysis team' in the analysis of the data. Preliminary results have already been published. Data taking and analysis will continue for the next few years. The Muon Lifetime Experiment The Standard Model is a consise description of elementary particles, quarks and leptons, and their interactions, the strong and electroweak. Experiment must provide three independent quantities to characterize completely the electroweak interaction, and these quantities are taken from the most precise measurements. We have proposed to measure the muon lifetime to a higher precision and with this measurement determine the Fermi coupling constant to a precision of one part per million. The measurement will be done at the Paul Scherrer Institute (near Zurich, Switzerland).