During the past twenty years a theory has arisen that
attempts to explain the structure of baryons, such as the neutron and proton, held
together by the strong force. This theory identifies quarks as the basic
building blocks of the baryons. The quarks are believed to be point like,
have fractional charge, and like all Fermions, have intrinsic spin of 
.
However, one of the great challenges facing particle physics is to understand
how these elementary particles actually form the nucleon. It is a
particularly difficult question because the theory, known as quantum
chromodynamics, is extremely complicated in the regime where the quarks are
confined. The spin of the proton and neutron can be a unique aspect in which
to test the theory. Until 1987 the nucleon spin was thought to be a well
understood issue with the three quarks that make up the nucleon contributing
to the overall spin of the particle. However in that year an experiment at
CERN presented results that indicated that little of the proton spin is
carried by the quarks. This remarkable result has been confirmed by more
precise recent measurements at both CERN and the Stanford Linear Accelerator
Center (SLAC).
This project will involve the design and construction of target systems maintaining polarized neutrons or protons for use with the polarized electron beams at both TJNAF (CEBAF) and SLAC. Design changes will be made to the existing system used in the SLAC experiment in order to enhance its capability. The major initiative is the development and construction of an entirely new system to be used in a large acceptance detector at TJNAF (CEBAF). This project will allow the University of Virginia to maintain a leading role in some of the most important and intriguing questions in physics. The origin of the spin of the nucleon is still not resolved and the experiments that will use these systems will provide important new information.
The experimental programs involve collaboration of over twenty U.S., seven European, and two Japanese universities. Five of the twenty are from within the Commonwealth. During the next three years five Virginia graduate students and approximately fifteen undergraduates will work on this project. The University of Genoa will to play an active role in the project and will have physicists and students working at Virginia.