Constraining GsE and Gsm Via Parity-Violating Electron Scattering

Snyder, Ryan Alan, Department of Physics, University of Virginia
Cates, Gordon, Department of Physics, University of Virginia
Paschke, Kent, Department of Physics, University of Virginia
Liyanage, Nilanga, Department of Physics, University of Virginia

This thesis reports on the 2005 HAPPEX parity-violating measurements A PV in elastic scattering of 3 GeV electrons off hydrogen and 4 He targets at 〈θ lab 〉 ≈ 6.0 ◦ carried out in Hall A at the Thomas Jefferson National Accelerator Facility in Newport News, VA. The 4 He result is A He PV = +6.40 ± 0.23 (stat) ± 0.12 (syst) ppm. The hydrogen result is A H PV = −1.60 ± 0.12 (stat) ± 0.05 (syst) ppm. These results significantly improve the constraints on the electric and magnetic strange form factors G s E and Gs M . We extracted G s E = −0.02 ± 0.014 (stat) ± 0.007 (syst) at 〈Q2 〉 = 0.077 GeV 2 from the 4 He result and the linear combination G s E + 0.088Gs M = 0.007 ± 0.011 (stat) ± 0.004 (syst) ± 0.005 (FF) at 〈Q 2 〉 = 0.109 GeV 2 from hydrogen. These results provide new limits on the role of strange quarks in the nucleon charge and magnetization distributions. This thesis reports on both the 4 He and hydrogen analysis of the 2005 data set with a particular focus on the background contamination for each measurement. An additional focus here is given to understanding and minimizing helicity-correlated asymmetries on the electron beam, systematic errors we needed to control at levels well below that of the measured parity-violating asymmetries A PV .

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PHD (Doctor of Philosophy)
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