Extracting the Spin Polarizabilities of the Proton by Measurement of Compton Double-Polarization Observables

The Compton double-polarization observable Sigma(2z) has been measured for the first time in the Delta(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 -2.87 0.52, gamma(E1E1) = 2.70 0.43, gamma(E1M2) = in gamma(E1M2) = -0.85 +/- 0.72, and gamma(M1E2) = 2.04 +/- 0.43, in units of 10(-4) fm(4).