Elastic and inelastic Compton scattering from deuterium at HIγS

The electromagnetic scalar polarizabilities (α, β) are fundamental structure constants of the nucleon, and precise experimental measurements of these are vital for a complete understanding of the nucleon’s internal structure. The scalar polarizabilities can be accessed via Compton scattering reactions, where the forward-angle scattering cross sections are more sensitive to α+β, while the backward-angle cross sections are more sensitive to α-β. Since the value of α+β is alternately given in a model-independent manner by the well-known Baldin sum rule, backward-angle cross sections are sufficient to obtain the individual polarizability values. A series of Compton scattering experiments is underway at the High Intensity Gamma-Ray Source (HIγS) at Triangle Universities Nuclear Laboratory, with the goal of extracting the electromagnetic scalar polarizabilities of the neutron (α_n, β_n). Two experiments were performed using a liquid deuterium target at incident photon energies of 61 and 81 MeV. Backward-angle scattering cross sections were measured using two large-volume high-resolution NaI detectors (DIANA and BUNI). The combined effect of the quasi-monoenergetic beam at HIγS and the excellent energy resolution of these detectors was adequate to resolve the inelastic contribution at two backward angles (115^o, 150^o). Preliminary elastic and inelastic cross section data at both 61 and 81 MeV will be presented.