Precision Measurements of the Nucleon Strange Form Factors at Q^2 ~0.1 GeV^2

Abstract

We report new measurements of the parity-violating asymmetry A_PV in elastic scattering of 3 GeV electrons off hydrogen and 4He targets with <theta_lab>~6.0 degrees. The 4He result is A_PV = (+6.40 +/- 0.23 (stat) +/- 0.12 (syst)) x10^-6. The hydrogen result is A_PV = (-1.58 +/- 0.12 (stat) +/- 0.04 (syst)) x10^-6. These results significantly improve constraints on the electric and magnetic strange form factors G_E^s and G_M^s. We extract G_E^s = 0.002 +/- 0.014 +/- 0.007 at <Q^2> = 0.077 GeV^2, and G_E^s + 0.09 G_M^s = 0.007 +/- 0.011 +/- 0.006 at <Q^2> = 0.109 GeV^2, providing new limits on the role of strange quarks in the nucleon charge and magnetization distributions.