Extracting neutron polarizabilities from Compton scattering on quasi-free neutron in $\gamma d \to \gamma n p$

Abstract

Compton scattering processes are ideal to study electric and magnetic dipole polarizabilities of nucleons. These fundamental quantities parametrize the responses of the internal degrees of freedoms to a monochromatic photon probe. In this work, the inelastic channel γd → γnp is treated in χEFT, with a focus on the kinematic region of the neutron quasi-free peak, where the momentum of the outgoing proton is small enough that it is considered to remain at rest. This provides access to the Compton scattering process γn → γn, from which the scalar polarizabilites of the neutron, α E1 and β M1 , are extracted. Using χEFT, triple differential cross-sections d 3 σ /dE n dΩ γ ′ Ω n in the photon energy range of 200-to-400 MeV are computed. The biggest contribution comes from the impulse approximation, with small corrections stemming from final state interactions, meson exchange currents and rescattering. In this presentation, we report progress and preliminary results.

International workshop on next generation gamma-ray source

“…Measurements of the neutron-photon interaction in QF kinematics therefore provide another avenue to extract neutron polarizabilities. High-quality theory is needed to control the corrections to the QF approximation (for first steps see reference [186]).…”

Theoretical aspects of Chiral Dynamics

“…As mentioned above, the value of the subtraction function at q 2 = 0 is related to the polarizabilities of the nucleon. The status of our knowledge of these quantities is discussed in several talks given at this workshop [110,111,112,113,114,115]. Since Reggeon dominance determines the subtraction function, it also leads to a prediction for the difference between the polarizabilities of proton and neutron.…”