Measurements of Double-Polarized Compton Scattering Asymmetries and Extraction of the Proton Spin Polarizabilities

Abstract

The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to measure the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the $\Delta (1232)$ region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields ${\gamma }_{E1E1}=-3.5\pm 1.2$, ${\gamma }_{M1M1}=3.16\pm 0.85$, ${\gamma }_{E1M2}=-0.7\pm 1.2$, and ${\gamma }_{M1E2}=1.99\pm 0.29$, in units of $10^{-4}$ fm${}^4$.

arXiv comment5 pages, 3 figures, 2 tables

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• Nucleon resonances in Compton scattering
• Designing Optimal Experiments: An Application to Proton Compton Scattering
• Determination of the scalar polarizabilities of the proton using beam asymmetry ${\Sigma }_3$ in Compton scattering
• Generalized polarizabilities of the nucleon in baryon chiral perturbation theory
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• Sum rules across the unpolarized Compton processes involving generalized polarizabilities and moments of nucleon structure functions
• First extraction of the scalar proton dynamical polarizabilities from real Compton scattering data
• Virtual Compton Scattering and Nucleon Generalized Polarizabilities
• Spin-dependent sum rules connecting real and virtual Compton scattering verified
• Spin polarizabilities of the proton by measurement of Compton double-polarization observables
• Partial-wave analysis of proton Compton scattering data below the pion-production threshold
• Comprehensive Study of Observables in Compton Scattering on the Nucleon
• Chiral Effective Theory Methods and their Application to the Structure of Hadrons from Lattice QCD
• Elastic Compton Scattering from 3He and the Role of the Delta
• Nucleon polarizabilities in covariant baryon chiral perturbation theory with explicit $\Delta$ degrees of freedom
• QCD and Hadron Physics
• First concurrent extraction of the leading-order scalar and spin proton polarizabilities
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