S2: Accomplishments of the second funding period

In the second funding period we focus on the following areas of research:
  • Scalar polarizabilities of the proton from both the beam asymmetry \(\Sigma_3\) and differential cross section in Compton scattering (\(\gamma p \to \gamma p\)) below pion threshold with an unpolarized hydrogen target.  Results from a proof-of-principle test measurement have been published [10.1140/epja/i2017-12203-0] [A2 Collaboration].
  • Spin polarizabilities of the proton via Compton scattering in the \(\Delta(1232)\) region, both from the beam-target asymmetries \(\Sigma_{2x}\) and \(\Sigma_{2z}\) with a polarized hydrogen target, and from the beam asymmetry \(\Sigma_3\) from an unpolarized target. Results from the first beam-target asymmetry have been published [10.1103/PhysRevLett.114.112501] [A2 Collaboration].

Proton Compton scattering beam-target asymmetry \(\Sigma_{2x}\) along with dispersion relation theory curves, taken from [10.1103/PhysRevLett.114.112501].

  • A model-independent partial-wave analysis of Compton scattering data, with the aim of extracting the static and dynamic polarizabilities of the proton, has been developed  [10.1016/j.physletb.2018.04.066], and will be used to interpret the new data.
  • Polarized and unpolarized active target developments to access both proton and neutron observables [10.22323/1.243.0005] [A2 Collaboration].
  • Neutron polarizabilities from Compton scattering and inclusive measurements on the deuteron and helium [10.22323/1.253.0092] [A1 and A2 Collaborations].
  • Precise measurements of the electrodisintegration of the deuteron at small momentum transfers [A1 Collaboration].
  • Theoretical description of the timelike nucleon structure in the process of di-lepton photoproduction. Feasibility studies for di-lepton photoproduction experiments [A2 Collaboration].
  • Feasibility studies for polarizability measurements at the upcoming MESA facility.
  • Chiral effective-field theory for nucleon and light-nuclear polarizabilities.  Calculations of the nucleon and nuclear polarizability effects in muonic atoms.