Constraining GsE and Gsm Via Parity-Violating Electron Scattering

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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