Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio to High Momentum Transfer
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
The electromagnetic form factors of the nucleon characterize the effect of its internal structure on its response to an electromagnetic probe as studied in elastic electronnucleon scattering. These form factors are functions of the squared four-momentum transfer Q2 between the electron and the proton. The two main classes of observables of this reaction are the scattering cross section and polarization asymmetries, both of which are sensitive to the form factors in different ways. When considering large f momentum transfers, double-polarization observables offer superior sensitivity to the electric form factor. This thesis reports the results of a new measurement of the ratio of the electric and magnetic form factors of the proton at high momentum transfer using the recoil polarization technique. A polarized electron beam was scattered from a liquid hydrogen target, transferring polarization to the recoiling protons. These protons were detected in a magnetic spectrometer which was used to reconstruct their kinematics, including their scattering angles and momenta, and the position of the interaction vertex. A proton polarimeter measured the polarization of the recoiling protons by measuring the azimuthal asymmetry in the angular distribution of protons scattered in CH2 analyzers. The scattered electron was detected in a large acceptance electromagnetic calorimeter in order to suppress inelastic backgrounds. The measured ratio of the transverse and longitudinal polarization components of the scattered proton is directly proportional to the ratio of form factors GpE=GpM. The measurements reported in this thesis took place at Q2 =5.2, 6.7, and 8.5 GeV2, and represent the most accurate measurements of GpE in this Q2 region to date.
- Research Organization:
- Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- AC05-06OR23177
- OSTI ID:
- 979064
- Report Number(s):
- JLAB-PHY-09-1127; DOE/OR/23177-1199; TRN: US201010%%379
- Country of Publication:
- United States
- Language:
- English
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