Compton Scattering at HIGS

The static electric and magnetic nucleon dipole polarizabilities will be determined from mea- surements of the cross section and polarized beam asymmetry for scattering of ~100 MeV gamma rays from hydrogen and deuterium targets at the HI--?S laboratory at Duke University. Scattered gamma rays will be detected with DIANA, the University of Kentucky’s 57 cm f × 48 cm NaI crys- tal, optimized for low-background counting at high photon energy. The measured intrinsic energy resolution of this detector is better than 1.6% fwhm near 100 MeV. We propose a measurement of both polarized-beam elastic scattering from the deuteron to determine the neutron electric and magnetic dipole polarizabilities, and scattering of polarized photons from the proton to determine its electric polarizability. Both of these are approved experiments at HI--?S. We also propose to perform feasibility measurements for elastic Compton scattering from 7Li. Recent Chiral Effective Field Theory calculations of elastic photon scattering, optimized for the energy range of present interest, are used to relate the measured observables to the static polarizabilities. The proposed project follows our recent successful work using the DIANA detector at Lund University, where elastic photon scattering cross sections were measured on deuterium and lithium targets using tagged photons over the range from 80 to 140 MeV. By relocating DIANA to HI--?S, we will be able to take full advantage of the unique features of the beam available at that facility. The proposed experiments align well with the DOE’s priority area of measuring properties of the neutron, and the Medium Energy Nuclear Physics Office’s goal of developing experimental tests of QCD.