Using effective field theory to analyse low-energy Compton scattering data from protons and light nuclei

TL;DR

This paper uses chiral effective field theory to analyze low-energy Compton scattering data from protons and light nuclei, extracting nucleon polarisabilities with high precision and discussing future experimental and theoretical directions.

Contribution

It provides new fits to proton and deuteron Compton scattering data using ChiEFT, improving the extraction of nucleon polarisabilities and constraining resonance parameters.

Findings

Proton electric polarisability .7 b1 0.3 (stat) b1 0.2 (Baldin) b1 0.8 (theory)

Proton magnetic polarisability .1 b1 0.3 (stat) b1 0.2 (Baldin) b1 0.8 (theory)

Deuteron and isoscalar polarisabilities consistent with previous results

Abstract

Compton scattering provides important insight into the structure of the nucleon. For photons up to about 300 MeV, it is parameterised by six dynamical dipole polarisabilities which characterise the response of the nucleon to a monochromatic photon of fixed frequency and multipolarity. Their zero-energy limit yields the well-known static electric and magnetic dipole polarisabilities \alpha and \beta, and the four dipole spin polarisabilities. Chiral Effective Field Theory (ChiEFT) describes nucleon, deuteron and 3-He Compton scattering, using consistent nuclear currents, rescattering and wave functions. It can thus also be used to extract useful information on the neutron amplitude from Compton scattering on light nuclei. We summarise past work in ChiEFT on all of these reactions and compare with other theoretical approaches. We also discuss all proton experiments up to about 400 MeV, as well as the three modern elastic deuteron data sets, paying particular attention to precision and accuracy of each set. Constraining the Delta(1232) parameters from the resonance region, we then perform new fits to the proton data up to omega(lab)=170 MeV, and a new fit to the deuteron data. After checking in each case that a two-parameter fit is compatible with the respective Baldin sum rules, we obtain, using the sum-rule constraints in a one-parameter fit, \alpha=10.7\pm0.3(stat)\pm0.2(Baldin)\pm0.8(theory), \beta=3.1\mp0.3(stat)\pm0.2(Baldin)\pm0.8(theory), for the proton polarisabilities, and \alpha =10.9\pm 0.9(stat)\pm0.2(Baldin)\pm0.8(theory), \beta =3.6\mp 0.9(stat)\pm0.2(Baldin)\pm0.8(theory), for the isoscalar polarisabilities, each in units of 10^(-4) fm^3. We discuss plans for polarised Compton scattering, their promise as tools to access spin polarisabilities, and other future avenues for theoretical and experimental investigation.