Elastic Compton Scattering on ³He at 100 MeV: Better Understanding the Neutron Static Scalar Polarizabilities

The nucleon electric and magnetic polarizabilities (α_E1 and β_M1) are fundamental quantities encoding the internal structure of the nucleon. They characterize the response of the nucleon to an external electromagnetic field and can be probed using nuclear Compton scattering. From chiral Effective Field Theories (χEFTs), the angular distributions of the Compton differential cross sections for light nuclei (A=1-6) provide an important way of extracting the nucleon static electromagnetic polarizabilities. However, due to experimental challenges, α_E1 and β_M1 of the nucleons, particularly of the neutron, are still not precisely determined.

Compton-scattering measurements at 61 and 100 MeV were conducted using a liquid ³He target and a circularly polarized photon beam at the High-Intensity Gamma-Ray Source (HIγS) facility at Triangle Universities Nuclear Laboratory (TUNL) in the summer of 2024. These experiments are the world’s first Compton-scattering measurements performed on a ³He target. Compared to Compton-scattering experiments on liquid deuterium and ⁴He, the elastic Compton cross section of ³He arises from a different linear combination of the nucleon contributions. This can provide another way to extract the polarizabilities of the neutron and another test under the χEFT formalism, although nuclear effects need to be taken into account.

In this talk, we will present preliminary results for the elastic Compton-scattering experiment on ³He at 100 MeV.