Understanding nucleon structure is one of the prime objectives of contemporary Nuclear Physics. This dissertation examines neutron electromagnetic structure, specifically the neutron polarizabilities, through Compton scattering on the deuteron and 3He. Experiments and theory in the past decade or so have improved our understanding of proton polarizabilities, but those of the neutron still remain “elusive”. In this thesis, we report the first calculations for γ3He scattering. We also report the first calculations in Chiral Perturbation Theory for polarized γd scattering.
Our calculations for elastic γd scattering show that the beam asymmetry, Σ is not a good observable to extract the spin-independent polarizabilities, αn or βn, and that the double-polarization observable, Δx, is sensitive to a linear combination of two of the neutron spin polarizabilities, γ1n and γ3n. Including the Δ-isobar explicitly in our calculations enhances the sensitivity of Δx to γ1n and γ3n and also identifies Δz as a possible observable to measure a linear combination of γ1n, γ2n, and γ4n at forward angles.
Our results for elastic γ3He scattering are quite encouraging for the extraction of neutron polarizabilities. The unpolarized dcs can be used to measure αn and βn. Meanwhile, Δz and Δx are sensitive to two different linear combinations of the neutron spin polarizabilities, γ1n, γ2n, and γ4n. Taken in concert with our γd results, this suggests that a combination of experiments and further theoretical efforts will provide an extraction of the neutron polarizabilities.
Since this project involves nuclear targets, we also model the NN interaction in the 1S 0 channel to better comprehend the forces that hold nuclei together. We investigate whether a perturbation expansion can be built for at least a part of the interaction. We have been successful in building such an expansion where we regulate the strong short-range pieces by a ‘slanty’ well with finite range (>1.5 fm) and treat the weak longer-range pieces perturbatively.