Nucleon Polarizabilities and Elastic Compton Scattering on 3He at HIγS*

The electric and magnetic polarizabilities (αE1 and βM1 ) are fundamental quantities encoding the internal structure of nucleons. They characterize the response of the nucleon to an external electromagnetic field and can be probed using Compton scattering processes. From chiral effective field theories ( χ EFTs) [1,2], the angular distributions of the Compton differential cross section for light nuclei (A=1-6) provide an important way of extracting the nucleon electromagnetic polarizabilities experimentally. However, due to the difficulties in experimental measurements, αE1 and βM1 of nucleons, particularly of the neutron, are still not precisely determined [3-5].

Compton scattering measurements using a liquid H3e target are planned for determining neutron electromagnetic polarizabilities. These measurements will be carried out using the nearly monoenergetic gamma-ray beam at the High Intensity Gamma-Ray Source (HIγS) facility at Triangle Universities Nuclear Laboratory (TUNL). This experiment will be the first Compton-scattering measurement performed on He 3, mainly because of limitations of cryogenic techniques, which have been recently overcome. Compared to Compton Scattering experiments on liquid deuterium [6] and He 4 [7,8], the elastic Compton cross section of He 3 arises from a different combination of the nucleon contributions. This can provide another way to extract the polarizabilities of the neutron and another test under the EFT formalism [9], although nuclear effects need to be taken into account. The proposed experiment will measure the angular differential cross section for Compton scattering from He 3 at 100 MeV using a circularly polarized photon beam at HIγS. In this talk, we will present the techniques and proposed setup of this experiment as well as the latest update about the research and development test.