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Title: Proton form factor ratio, μ pG E P/G M P from double spin asymmetry

The form factors are fundamental properties of the nucleon representing the effect of its structure on its response to electromagnetic probes such as electrons. They are functions of the four-momentum transfer squared Q 2 between the electron and the proton. This thesis reports the results of a new measurement of the ratio of the electric and magnetic form factors of the proton up to Q 2 = 5.66 (GeV/c) 2 using the double spin asymmetry with a polarized beam and target. Experiment E07-003 (SANE, Spin Asymmetries of the Nucleon Experiment) was carried out in Hall C at Jefferson Lab in 2009 to study the proton spin structure functions with a dynamically polarized ammonia target and longitudinally polarized electron beam. By detecting elastically scattered protons in the High-Momentum Spectrometer (HMS) in coincidence with the electrons in the Big Electron Telescope Array (BETA), elastic measurements were carried out in parallel. The elastic double spin asymmetry allows one to extract the proton electric to magnetic form factor ratio G p E/G p M at high-momentum transfer, Q 2= 5.66 (GeV/c) 2. In addition to the coincidence data, inclusively scattered electrons from the polarized ammonia target were detected by HMS, which allows to measuremore » the beam-target asymmetry in the elastic region with the target spin nearly perpendicular to the momentum transfer, and to extract G p E/G p M at low Q 2= 2.06 (GeV/c) 2. This alternative measurement of G p E/G p M has verified and confirmed the dramatic discrepancy at high Q 2 between the Rosenbluth and the recoil-polarization-transfer iv method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The measurement of the form factor ratio at Q 2 = 2.06 (GeV/c) 2 has been determined as {mu}{sub p}G p E/G p M = 0.605{+-}0.178 stat{+-}0.033 sys which is in agreement with an earlier measurement with the polarized target technique at similar kinematics. The measurement of the form factor ratio at Q 2 = 5.66 (GeV/c) 2 has been determined as μ pG p E/G p M = 0.672 {+-} 0.362 stat which represents the highest Q 2 reach with the double spin asymmetry to date.« less
  1. Hampton Univ., Hampton, VA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
JLAB-PHY-13-1822; DOE/OR/23177-2905
DOE Contract Number:
Resource Type:
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States