Extracting the spin polarizabilities of the proton by measurement of Compton double-polarization observables

The Compton double-polarization observable ς2z has been measured for the first time in the Δ(1232) resonance region using a circularly polarized photon beam incident on a longitudinally polarized proton target at the Mainz Microtron. This paper reports these results, together with the model-dependent extraction of four proton spin polarizabilities from fits to additional asymmetry data using either a dispersion relation calculation or a baryon chiral perturbation theory calculations with the weighted average of these two fits resulting in γE1E1=-2.87±0.52, γM1M1=2.70±0.43, γE1M2=-0.85±0.72, and γM1E2=2.04±0.43, in units of 10-4fm4.