New results from the HAPPEX Experiments at Q2 = 0.1GeV/c2

Abstract

The nucleon’s strange electric and magnetic form factors G E s and G M s can be probed via parity-violating electron scattering. The HAPPEX Collaboration has made new measurements of the parity-violating asymmetry A PV in elastic scattering of 3 GeV electrons off hydrogen and 4He targets with ≈ 6.0°. For 4He the preliminary result is A PV = (+6.43 ± 0.23 (stat) ± 0.22 (syst)) × 10−6. For hydrogen the preliminary result is A PV = (−1.60 ± 0.12 (stat) ± 0.05 (syst)) × 10−6. From these values we extract G E s = 0.004 ± 0.014 ± 0.013 at = 0.077 GeV/c 2, and G E s + 0.09G M s = 0.004 ±0.011 ± 0.005 at = 0.109 GeV/c 2, both consistent with zero, providing stringent new limits on the role of strange quarks in the vector structure of the nucleon.