This project addresses certain fundamental aspects, especially symmetries, of the electroweak and strong interactions that are reflected in meson and nucleon properties, structure and interactions at low/intermediate energies. This research is motivated by the fact that the present comprehensive theory--the Standard Model (SM)--is known to be incomplete; furthermore, the SM becomes unworkable for strong interactions at low energies. The rare beta decay of the pi-meson (pion), occurring once in about 100 million ordinary pion decays, provides a theoretically clean window to certain allowed extensions of the SM. The PIBETA experiment, mounted at the Paul Scherrer Institute, Switzerland, by an international collaboration of seven institutions led by the UVa group, aims to improve the present 4% accuracy of the pion beta decay rate by better than a factor of ten in a staged approach, in order to match the theoretical uncertainty and provide new constraints on physics beyond the SM. Measurements will begin in the summer of 1998 and will continue for several years. PIBETA is the main effort of the present research proposal. Additional commitments of effort include work on studies of nucleon and meson structure at Stanford (SLAC experiment E155) and Jefferson Lab (CLAS and RADPHI collaborations). Lastly, this group's work on chiral symmetry breaking in the pion-pion and pion-nucleon systems is being completed and published. (Chiral symmetry is the organizing principle in low-energy strong interactions.) During the past four years this program has resulted in two doctoral and one master's degree at UVa. Two more UVa Ph.D. degrees are expected in the next three years, plus three more at collaborating universities stemming from the PIBETA project alone. Each year typically one to two undergraduate students are engaged in research on this project, thus gaining practical laboratory experience. ***
