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Title A Precision Measurement of the Transverse Asymmetry A_T' from Quasi-elastic ^3He(e,e¿) process, and the Neutron Magnetic Form Factor GNM at low Q^2
Authors Wang Xu
JLAB number JLAB-PHY-02-110
LANL number (None)
Other number DOE/ER/40150-2770
Document Type(s) (Thesis) 
Supported by U.S. Naval Research: No
Supported by Jefferson Lab LDRD Funding: No
A PHD thesis
Advisor(s) :
   Haiyan Gao (MIT)
Publication Abstract: Electromagnetic form factors are fundamental quantities in describing the underlying electromagnetci structure of nucleons. While proton electromagnetic form factors have been determined with good precision, neutron form factors are known poorly, largely due to the lack of free neutron targets. Jefferson Lab Hall A experiment E95-001, a "precise measurement of the transverse asymmetry A_T' from the quasielastic ^3{polarized}He({polarized}e, e') process," was therefore designed to determine precisely the neutron magnetic form factor, G^n_M at low momentum transfer values and was successsfully completed in Spring 1999. High precision A_T'data in the quasi-elastic region at Q^2 values of 0.1 to 0.6 (GeV/c)^2 were obtained using a high-pressure spin-exchange optically-pumped polarized ^3He gas target with an average polarization of 30%, a longitudinally polarized e^- beam, and two High Resolution Spectrometers: HRSe and HRSh. HRSe was employed to detect scattered electrons from the quasi-elastic kinematic region, and HRSh was employed as a elastic polarimetry to monitor the product of the beam and target polarizations. The extraction of form factors is usually model-dependent. Significan constraints on theoretical calculations are provided bu additional high precision quasi-elastic asymmetry data at Q^2 values of 0.1 and 0.2 (GeV/c)^2 in ^3He breakup region, where effects of final state interactions (FSI) and meson exchange currents (MEC) are expected to be large [71]. G^n_M is extracted from a non-relativistic Faddeev calculation which includes both FSI and MEC at Q^2 values of 0.1 and 0.2 (GeV/c)^2. The uncertainties of G^n_M at these Q^2 values are comparable to those of recent experiments with deuterium targets [58]. At the higher Q^2 values from this experiment, G^n_M is extracted from Plane-Wave Impulsive Approximation (PWIA) calculations with a relatively large theoretical uncertainty of 2-4%. Thus a reliable extraction of G^n_M from A_T' at higher Q^2 values (especially at Q^2 values of0.3 and 0.4 (GeV/c)^2) requires improved theoretical calculations including FSI, MEC, and relativistic effects. However, those G^n_M results extracted from PWIA at higher Q^2 values from the experiment still show overall a good agreement with the most recent deuterium measurements. The analysis of asymmetries and the extraction of G^n_M from both the Faddeev calculations and the PWIA calculations are reported in this thesis.
Experiment Numbers: E95-001
Group: Hall A
Document: pdf
Accepted Manuscript:
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