Measurement of the Beam-Recoil Polarization in Low-Energy Virtual Compton Scattering from the Proton

TL;DR

This study measures the beam-recoil polarization in low-energy virtual Compton scattering from the proton, extracting a new structure function that informs about the proton's generalized polarizabilities.

Contribution

It presents the first measurement of the structure function $P_{LT}^ot$ in virtual Compton scattering, providing new insights into proton structure.

Findings

Measured double-polarization observables at $Q^2=0.33$ GeV^2.

Extracted the structure function $P_{LT}^ot$ for the first time.

Provided a new linear combination of proton's generalized polarizabilities.

Abstract

Double-polarization observables in the reaction $\vec{e}p \rightarrow e'\vec{p'}\gamma{}$ have been measured at $Q^2=0.33 (GeV/c)^2$. The experiment was performed at the spectrometer setup of the A1 Collaboration using the 855 MeV polarized electron beam provided by the Mainz Microtron (MAMI) and a recoil proton polarimeter. From the double-polarization observables the structure function $P_{LT}^\perp$ is extracted for the first time, with the value $(-15.4 \pm 3.3 (stat.)^{+1.5}_{-2.4} (syst.)) GeV^{-2}$, using the low-energy theorem for Virtual Compton Sattering. This structure function provides a hitherto unmeasured linear combination of the generalized polarizabilities of the proton.