Research in Intermediate Energy Physics

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This project addresses certain fundamental aspects of the electroweakand strong interactions that are reflected in meson and nucleonproperties and interactions at low/intermediate energies. Theresearch is motivated by the fact that the present comprehensivetheory--the Standard Model (SM)--is known to be incomplete;furthermore, the SM becomes unworkable for strong interactions at lowenergies.The rare beta decay of the pi-meson (pion), occurring once in about100 million ordinary pion decays, provides a theoretically cleanwindow to certain allowed extensions of the SM. The PIBETAexperiment, mounted at the Paul Scherrer Institute, Switzerland, by aninternational collaboration of seven institutions led by theUniversity of Virginia (UVa) group, aims to improve the present 4%accuracy of the pion beta decay rate by about a factor of ten in astaged approach, in order to match the theoretical uncertainty andprovide new constraints on physics beyond the SM. Measurements thatbegan in 1999 will continue through 2001. PIBETA is the main effortof the present research project. Additional commitments of effortinclude work on studies of nucleon and meson structure at Stanford(SLAC) and Jefferson Lab (CLAS collaboration).During the past three years this program has resulted in two doctoraldegrees at UVa plus three more at collaborating universities stemmingfrom the PIBETA project alone. Four more UVa Ph.D. degrees areexpected in the next three to four years. Each year typically one totwo undergraduate students are engaged in research on this project,thus gaining practical laboratory experience.