Measurement of the Neutron Elastic Electromagnetic Form Factor Ratio at Large Momentum Transfer 312 views

Exploring nucleon structure is vital both for understanding its origin and existence as well as for the advancement of the sciences. It helps us answer key questions such as how quark and gluon dynamics create 99% of the nucleon mass. Electron - nucleon scattering has been widely used for precision studies of the nucleon and nuclear structure since the Nobel Prize winning investigations by Robert Hofstadter and collaborators in the 1950s. These studies provide information about the spatial charge and current densities of the nucleon in terms of the electromagnetic form factors. The form factors are functions of four momentum transfer squared (Q^2). Extending the electromagnetic form factor measurements to higher Q^2 plays a critical role in furthering the understanding of nucleon structure. This motivated the Super BigBite Spectrometer (SBS) program at Jefferson Lab. The open nature of the spectrometers and the direct line of sight from the target to the tracking detector locations in experimental setups such as SBS creates high levels of background at the detectors. This necessitates the use of tracking detectors with high rate capability and good position resolution. Gas Electron Multiplier (GEM) detectors are an excellent choice for tracking detectors in such experiments. Understanding the performance of the GEM detectors is important not just for SBS experiments but also for future high-luminosity experiments. This thesis reports the exploratory results from the measurement of the neutron elastic electromagnetic form factor ratio (GEn /GMn ) at high momentum transfer. A longitudinally polarized electron beam was scattered off a polarized ^3He target, used as an effective polarized neutron target. In this experiment, the polarized ^3He target achieved a world record polarization weighted luminosity at a beam current of 45 µA. Double spin asymmetry of the scattered neutron events is used to extract the neutron form factor ratio. Measurements were taken at Q^2 = 3.0, 6.8, 9.8 (GeV/c)^2 . The lowest Q^2 measurement is in good agreement with the existing world data, and the higher-Q^2 measurements extend the Q^2 reach well beyond the existing world data and are expected to remain unmatched for a long time.

PHD (Doctor of Philosophy)

Nucleon Electromagnetic Form Factors; Neutron Electric Form Factor; GEn; SBS; GEMs; JLab

English

2026-04-30