The group doing experimental nuclear physics at Illinois pursues its studies at a variety of accelerator facilities throughout the world, using high-energy beams of electrons, photons, muons, and antiprotons.

Nuclear Physics Studies Using Beams of Photons 8]

These activities take place at CEBAF located in Newport News, Va., and at the Saskatchewan Accelerator Laboratory in Canada and consist of two basic types of studies: photon scattering and photodisintegration of light nuclear systems. The primary goal of the photon scattering is to measure the electric and magnetic polarizabilities of both free and bound nucleons. The photodisintegration studies concentrate on precision measurements of the photodisintegration of light nuclei, such as deuterium. The deuteron photodisintegration is one of the most fundamental processes in all of nuclear physics and involves such questions as the form of the nuclear current operator, the role of relativity, and mesonic exchange currents. A series of experiments is just beginning at CEBAF. These experiments 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 CEBAF.

Nuclear Physics Studies Using Beams of Electrons

There are three specific 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, will measure the strange quark contribution to the magnetic moment of the proton and will take data at the MIT/Bates Linear Accerator. A far more ambitious program is the G0 experiment, which will take place at a new national electron facility, CEBAF, located in Newport News, Va. It involves the construction of a novel and dedicated magnetic spectrometer. The entire effort is being spearheaded by the Illinois group. Second is a series of experiments (HERMES), which will measure the spin structure function of the proton and neutron by scattering longitudinally polarized electrons from polarized protons and neutrons. This will allow one to determine how much each type of quark contributes to the spin of the nucleon. The experiments are underway at the DESY facility in Hamburg, Germany. One of the principal contributions of the Illinois group to the collaboration is the design and construction of laser-driven polarized hydrogen and deuterium targets to be used in the experiments. Third is an experiment to measure the electric quadrupole contribution to the nucleon-to-delta transition. Such a contribution might provide the first evidence that the proton is not a spherical object but rather deformed into a football-like shape. The requirements of the experiment have led to the development of a new experimental technique known as out-of-plane spectroscopy (OOPS). The Illinois group, in collaboration with MIT and others, has led the effort to design and build the necessary apparatus as well as define the physics opportunities that the new technique provides.

Physics Using Beams of Antiprotons
These experiments involve work at the Low Energy Antiproton Ring (LEAR) at CERN, the multinational European accelerator complex located in Geneva. With several other institutions, we are studying two topics in antiproton physics that are of high present interest, both involving the production of strange quarks. The first topic involves hyperon production near threshold; the physics interest is to understand the dynamics of strangeness production in the low-energy regime. This is possible because the observables of the final state hyperons, which exhibit strangeness, are thought to mirror the behavior of the internal strange quark. The second topic features the investigation of reactions that can proceed through channels exhibiting large gluonic ``exotic'' matter (the so-called JETSET experiment). A major Illinois contribution to these projects was the construction of a novel electromagnetic calorimeter.

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 of 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 is building the major detectors, constructing novel electronics simulation systems, and developing a unique electron traceback system from state-of-the-art particle-tracking devices.