Scattering and Reactions of Intermediate Energy Projectiles

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This grant will support the experimental work of the Intermediate Energy Nuclear Physics Group at Rutgers University. This group carries out experiments with electron beams primarily at the new continuous electron beam accelerator, CEBAF, at the Jefferson Laboratory in Newport News, Virginia. They were leaders in designing and constructing a large polarimeter for this facility; it determines the direction of the spin of protons knocked out of the nucleus by the highly energetic electrons. Measurements with this polarimeter yield highly accurate information on the fundamental electromagnetic properties of the free proton, and should reveal possible changes in these properties when the proton is bound inside a nucleus. Related experiments will be carried out at lower energies at an accelerator in Mainz, Germany. Other such spin measurements will test simple quark model descriptions of reactions in which protons are emitted from a deuterium target by incident high-energy photons. The spin measurements are much more sensitive than previous experiments to possible problems in the quark description of the reaction. Finally, a third major program addresses directly the contributions of quarks to the spin of the neutron by examining changes in the probability for scattering electrons when the direction of the neutron's spin in the target is changed.