Double Polarization Experiments With Gamma Rays

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This proposal seeks support to finish data taking and begin analysis of the data from the double polarization experiments at the LEGS (Laser Electron Gamma Source) facility at Brookhaven National Laboratory. LEGS is a unique nuclear physics laboratory. It creates polarized gamma rays covering the (3,3) resonance energy region via back scattering of laser light from relativistic electrons that circulate in a storage ring. A novel polarized target of solid Hydrogen-Deuterium, SPHICE, has been developed. Previous data that studied neutral pion production are ultra clean. The final data will complete the charged particle final state experiments using a time projection chamber, large bore solenoidal magnet, and dedicated trigger detectors surrounding the target (the latter built by Virginia Tech). Data taken at the LEGS facility can address some of the most important problems in the structure of the nucleon, for example, the GDH sum rule can be tested for both neutrons and protons. This will lead to an improved model of nucleon spin structure. Also because many double polarization amplitudes and channels can be simultaneously measured, a complete set of pion-photo-production amplitudes can be worked out.