Precision Measurement of the proton neutral weak form factors at Q{sup 2} ~ 0.1 GeV{sup 2}

This thesis reports the HAPPEX measurement of the parity-violating asymmetry for longitudinally polarized electrons elastically scattered from protons in a liquid hydrogen target. The measurement was carried out in Hall A at Thomas Jefferson National Accelerator Facility using a beam energy E = 3 GeV and scattering angle <θ{sub lab}> = 6◦. The asymmetry is sensitive to the weak neutral form factors from which we extract the strange quark electric and magnetic form factors (G{sup s}{sub E} and G{sup s}{sub M}) of the proton. The measurement was conducted during two data-taking periods in 2004 and 2005. This thesis describes the methods for controlling the helicity-correlated beam asymmetries and the analysis of the raw asymmetry. The parity-violating asymmetry has been measured to be A{sub PV} = −1.14± 0.24 (stat)±0.06 (syst) ppm at <Q{sup 2}> = 0.099 GeV{sup 2} (2004), and A{sub PV} = −1.58±0.12 (stat)±0.04 (syst) ppm at <Q{sup 2}> = 0.109 GeV{sup 2} (2005). The strange quark form factors extracted from the asymmetry are G{sup s}{sub E} + 0.080G{sup s}{sub M} = 0.030 ± 0.025 (stat) ± 0.006 (syst) ± 0.012 (FF) (2004) and G{sup s}{sub E} +0.088G{sup s}{sub M} = 0.007±0.011 (stat)±0.004 (syst)±0.005 (FF) (2005). These results place the most precise constraints on the strange quark form factors and indicate little strange dynamics in the proton