January 30, 2014 - Special Theory Meeting

Meeting Logistics

OUR EXPERIMENTAL PROGRAM: To precisely measure scattering asymmetry of spin polarized electrons from thin pure Z foils; Accessible energy range is about 3 to 8 MeV; Targets on hand are gold, silver, copper foils of varying thickness, but can install others readily; Measure polarimeter systematics with goal <0.5%

OUR SIMULATION PROGRAM: Build GEANT4 model of polarimeter and benchmark detector response against measurement; Implement physics (cross-section, Sherman function, spin transfer functions) provided by theory; Develop ab initio simulation dependence of asymmetry on target thickness (multiple scattering, radiation effects, etc) to measurement; By calibrating model to experimental data predict zero-thickness asymmetry with high precision <1%

DESIRED THEORY PROGRAM: Provide physics tables for simulation (cross-section, Sherman function, spin transfer functions); Describe theoretical basis, corrections, uncertainties; Advise which measurements may be best tests on leading corrections or limit absolute knowledge of physics; Consider calculation to improve uncertainty in physics below 1%

Question #1 (Joe 1/13/2014): Coulomb screening is a leading effect for electron energies <1 MeV, and finite nuclear size is a leading effect for energies >10MeV (when DeBrogile wavelength is comparable to nuclear radius). Although our polarimeter is optimized for 5MeV we can operate with beam energies typically from about 3-8 MeV. What is the size of the uncertainty on the corrections in this energy range and for Z we use such as gold, silver, copper? Are we sensitive enough in this region to perform a test on the uncertainty of the physics calculations, e.g. using suitable Z or extending the energy reach?

Question #2 (Joe 1/15/2014): Is the biggest uncertainty in the theoretical calculations radiative corrections? Can a sound theoretical calculation be made that calculates this contribution with relative accuracy of ~30%?