Compton Scattering from Low-Z Nuclei and Determination of the Electromagnetic Polarizabilities of the Neutron*

The electromagnetic polarizabilities of the nucleon are fundamental structure constants that describe its response to external electric and magnetic fields. Neutron polarizabilities have relatively larger uncertainties compared to those of the proton. Chiral Effective Field Theory (χEFT) has been used to extract neutron polarizabilities from elastic Compton-scattering measurements on deuterium. Further developments in χEFT now allow for a meaningful interpretation of measurements on low-Z nuclear targets, such as 3He and 4He. The High Intensity Gamma-Ray Source (HIGS) at Triangle Universities Nuclear Laboratory (TUNL) delivers a monoenergetic photon beam that provides the external electromagnetic field to low-Z nuclear targets. We have utilized the unique capabilities of HIGS for recent measurements on 3He and are planning to continue with 4He measurements in the near future. In this talk, the methodology for extracting Compton-scattering cross sections will be described. An overview of the HIGS facility and previous experiments will be outlined, followed by a discussion of plans for future experiments.