Precision Measurement of the Spin-dependent Asymmetry in the Threshold Region of Quasielastic ³He

Thesis/Dissertation · Sun Sep 01 00:00:00 EDT 2002

DOI:https://doi.org/10.2172/824959· OSTI ID:824959

Xiong, Feng ^[1]

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1. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

The first precision measurement of the spin-dependent asymmetry in the threshold region of polarized ³He(polarized e, e') was carried out in Hall A at the Jefferson Laboratory, using a longitudinally polarized continuous electron beam incident on a high-pressure polarized ³He gas target. The polarized electron beam was generated by illuminating a strained GaAs cathode with high intensity circularly polarized laser light, and an average beam polarization of about 70% was achieved. The ³He target was polarized based on the principle of spin-exchange optical pumpint and the average target polarization was about 30%. The scattered electrons were detected in the two Hall A high resolution spectrometers, HRSe and HRSh. The data from HRSh were used for this analysis and covered both the elastic peak and the threshold region. Two kinematic points were measured in the threshold region, one with a central Q²-value of 0.1 (GeV/c)² at an incident beam energy E₀ = 0.778 GeV and the other with a central Q²-value of 0.2 (GeV/c)² at E-0 = 1.727 GeV. The average beam current was 10 mu-A, which was mainly due to the limitation of the polarized ³He target. The measured asymmetry was compared with both plane wave impulse approximation (PWIA) calculations and non-relativistic full Faddeev calculations which include both final-state interactions (FSIs) and meson-exchange currents (MECs) effects. The poor description of the data by PWIA calculations at both Q²-values suggests the existence of strong FSI and MEC effects in the threshold region of polarized ³He (polarized e, e'). Indeed, the agreement between the data and full calculations is very good at Q² = 0.1 (GeV/c)². On the other hand, a small discrepancy at Q² = 0.2 (GeV/c)² is observed, which might be due to some Q² -dependent effects such as relativity and three-nucleon forces (3NFs), which are not included in the framework of non-relativistic Faddeev calculations. Some preliminary results show that 3 NF effects are indeed non-negligible in the threshold region and more theoretical work is currently underway towards a better understanding of both effects. With recent development and success of the chiral perturbation theory, it is hopeful that a future application of the resulting chiral N N forces to electrodisintegration of ³He might solve the present discrepancy.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC05-84ER40150
• OSTI ID: 824959
• Report Number(s): JLAB-PHY-02-111; DOE/ER/40150-2771; TRN: US0402265
• Resource Relation: Other Information: TH: Thesis; Thesis information not provided; PBD: 1 Sep 2002
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ACCURACY
ASYMMETRY
BEAM CURRENTS
BOSON-EXCHANGE MODELS
CATHODES
CEBAF ACCELERATOR
ELECTRON BEAMS
ELECTRONS
ENANTIOMORPHS
FINAL-STATE INTERACTIONS
IMPULSE APPROXIMATION
PERTURBATION THEORY
POLARIZATION
SPECTROMETERS
SPIN EXCHANGE
TARGETS