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.
Bibliographical noteFunding Information:
The authors wish to acknowledge the excellent support of the accelerator group and operators of MAMI. We also wish to acknowledge and thank B. Pasquini and V. Pascalutsa for the use of their theory codes, as well as H. Grießhammer, J. McGovern, D. Phillips, and M. Vanderhaeghen for their theoretical support. This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC, FRN: SAPPJ-2015-00023), the U.S. Department of Energy (Offices of Science and Nuclear Physics, Awards No. DE-FG02-99-ER41110, No. DE-FG02-88ER40415, No. DEFG02-01-ER41194, and No. DE-SC0014323) and National Science Foundation (Grants No. PHY-1039130, No. PHY-1714833, and No. OISE-1358175), Deutsche Forschungsgemeinschaft (SFB443, SFB/TR16, and SFB1044), the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” program (Hadron Physics, Contract No. RII3-CT-2004-506078), Schweizerischer Nationalfonds (Contract Nos. 200020-156983, 132799, 121781, 117601, and 113511), the U.K. Science and Technology Facilities Council (STFC 57071/1, 50727/1, ST/L00478X/1, and ST/L005824/1), and INFN (Italy).
© 2020 authors.