Measurement of the Neutron Magnetic Form Factor at Large Momentum Transfer Using the Super-Bigbite Apparatus in Jefferson Lab Hall-A

The nucleon elastic electromagnetic form factors help us study the electromagnetic structure of the nucleon, benchmark theoretical models, and improve our understanding of non-perturbative quantum chromodynamics and confinement. The Nobel Prize-winning electron-nucleon scattering experiments by Robert Hofstadter and collaborators in the 1950s at Stanford High Energy Physics Lab were the first nucleon form factor measurements performed using leptonic probes. The Super Bigbite Spectrometer (SBS) program at Hall-A of Jefferson Lab represents the latest efforts to measure nucleon form factors. This ambitious program aims to significantly extend the current data set in terms of square momentum transfer (Q^2) with high precision. The advent of novel detector technologies, like Gas Electron Multipliers (GEM), which provide excellent position resolution (< 100 μm) while withstanding high background particle rates (several hundred MHz/cm^2) over a large active area, has paved the way for open-geometry, moderate solid angle spectrometers, which are central to all form factor experiments in the SBS program. The first experimental run group in SBS ran successfully between September 2021 and February 2022, collecting data for the measurement of the magnetic form factor of the neutron GMn at five squared momentum-transfer values: 3.0, 4.5, 7.5, 9.8, and 13.5 (GeV/c)^2. This extends the existing high-precision data for GMn by about a factor of four. The ratio technique was used, which involved the simultaneous measurement of exclusive quasielastic scattering of D(e,e′n)p and D(e,e′p)n from a deuterium target. Pre-preliminary results for D(e,e′n)p and D(e,e′p)n quasi-elastic ratio, and the neutron magnetic form factor GMn, for Q^2 points 3.0, 9.8, and 13.5 (GeV/c)^2 are presented.