Speaker
Description
The investigation of the spatial distributions of the charge and magnetism within nucleons remains a central problem in Hadronic Physics. The deviation from a point charge and point-like anomalous magnetic moment is characterized by introducing measurable observables as Form Factors (FFs). A clear discrepancy exists between FF ratios obtained using Rosenbluth separation and polarization transfer experiments. The results of polarization transfer experiments at the Jefferson Lab show a sharp drop in the FF ratio $\mu G_{Ep}/G_{Mp}$ starting $Q^2 \approx 1~\mathrm{GeV}^2$, pointing to a different $Q^2$ dependence of $G_{Ep}$ and $G_{Mp}$. The Super Bigbite (SBS) GEp-V experiment (E12-07-109) at the Jefferson Lab Hall A aims to extend the $Q^2$ reach of the FF ratio to $11~\mathrm{GeV}^2$. In the SBS GEp-V experiment, the Jefferson Lab's longitudinally polarized electron beam was scattered from an unpolarized liquid-hydrogen proton target, transferring polarization to the proton. The recoiling protons were detected in the Super BigBite Spectrometer, where the large dipole magnet caused spin precession, rotating the longitudinal polarization component into a normal component. The polarization components were then measured through secondary scattering in the downstream $CH_2$ analyzer. The proton-nucleus spin-orbit interaction with the analyzer material of the polarimeter result in an azimuthal asymmetry. Large-area GEM tracking detectors reconstructed the proton tracks before and after the analyzer, allowing the azimuthal asymmetry from the secondary scattering to be determined. The measured asymmetry provides access to the recoil-proton polarization components, whose ratio is directly related to the proton form factor ratio. The analysis is currently at the stage of detector calibrations. Progress is being made in optimizing software thresholds and pulse finding algorithms, Internal and Global detector alignments, and calorimeter timing and energy calibrations. An overview of the experiment and the current state of the analysis will be presented.
Acknowledgment: US Department of Energy, Office of Science, Office of Nuclear physics award number DE-FG02-03ER41240.