Elastic scattering of longitudinally polarized electrons from helium-4: A measurement of G(E)(S) at Q2 = 0.1 (GeV/c)2.

摘要

We have performed the first measurement of the parity-violating asymmetry in the elastic scattering of longitudinally polarized electrons from 4He. The kinematics chosen (Q 2 = 0.1 (GeV/c)2) provide a direct sensitivity to the strange electric form factor GsE with negligible contributions from competing effects. This experiment was performed in June 2004 and July-September 2005 in Hall A at Jefferson Lab. This work represents the experimental setup and analysis of the 2004 dataset.; The final statistical precision, from the combined datasets, put stringent requirements on the systematic errors that normalize the asymmetry (e.g. Q2, beam polarization, backgrounds). The experimental and analysis techniques, presented in this thesis, resulted in a 12.9% relative measure of the parity-violating asymmetry for the 2004 dataset, and a 4.1% relative measure for the 2005 dataset (the most precise measurement of a parity-violating asymmetry ever obtained).; The 2004 measured result, APV = 6.72 +/- 0.84 (stat) +/- 0.21 (syst) ppm, allows for the extraction of the electric strange form factor: GsE (Q2 = 0.1) = -0.038 +/- 0.042 (stat) +/- 0.010 (syst). When combined with results from previous experiments, at nearly the same kinematics, a clear picture of the contribution of strange quarks to the nucleon's electric and magnetic form factors emerges.