Spin polarizabilities of the proton by measurement of Compton double-polarization observables

TL;DR

This study measures the first double-polarization observable in proton Compton scattering in the $ ext{Δ}(1232)$ region and extracts proton spin polarizabilities using dispersion and chiral theories, providing new experimental data.

Contribution

First measurement of the $oldsymbol{ ext{Σ}_{2z}}$ observable in the $ ext{Δ}(1232)$ resonance region and extraction of proton spin polarizabilities from asymmetry data.

Findings

Measured $ ext{Σ}_{2z}$ in the $ ext{Δ}(1232)$ region for the first time.

Extracted four proton spin polarizabilities with specified values.

Results support theoretical models of proton structure.

Abstract

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 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 dispersion relation and chiral perturbation theory calculations, with the former resulting in: $\gamma_{E1E1} = -3.18 \pm 0.52$, $\gamma_{M1M1} = 2.98 \pm 0.43$, $\gamma_{E1M2} = -0.44 \pm 0.67$ and $\gamma_{M1E2} = 1.58 \pm 0.43$, in units of $10^{-4}~\mathrm{fm}^{4}$.