First quasi-elastic polarized electron scattering measurement of polarization transfer to protons in a complex nucleus: Oxygen-16

• Main Author: Wijesooriya, Krishni
• Format: Others
• Language: English
• Published: W&M ScholarWorks 1999
• Online Access: https://scholarworks.wm.edu/etd/1539623964; https://scholarworks.wm.edu/cgi/viewcontent.cgi?article=3583&context=etd

The first polarization transfer measurement in the (e,e' p) reaction on a complex nucleus, a study of the exclusive reaction O16e&ar; ,e'p&ar; 15N* , is discussed in this thesis. This experiment was performed at Jefferson Lab, using the Hall A Focal Plane Polarimeter. This was the first experiment to use polarized beam at Jefferson Lab. Simultaneous measurements were also made for the He&ar;, e'p&ar; reaction allowing a precise comparison between the form factor ratios for free and bound protons. Since the helicity-dependent, longitudinal P'l and transverse P't components of the polarization of the recoil proton are sensitive to the electromagnetic form factors GE and GM of the proton inside the nuclear medium, these polarization transfer observables can be used to look for possible medium modification effects on the form factor ratio for the bound proton. The systematic uncertainties involved in performing a recoil polarimetry measurement are minimal, and the theoretical uncertainty (mainly corrections to the Impulse Approximation) are also small. Therefore this measurement provides a sensitive test of the predictions of medium-induced changes in the form factor ratio. Results were obtained for two recoil momentum points, 85 and 140 MeV/c, at a Q2 of 0.8 (GeV/c)2 in quasielastic, perpendicular kinematics. Within statistical uncertainties, the results are in good agreement with theoretical calculations for the polarization observables obtained assuming free values for the form factors, i.e., the results are consistent with the absence of medium modifications of the nucleon electromagnetic structure. This experiment provides a strong basis for the forthcoming high precision measurements of the ratio GE/GM in the nuclear medium.