New results from the HAPPEX Experiments at Q2 = 0.1GeV/c2
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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 3GeV electrons off hydrogen and 4He targets with 〈θlab〉 ≈ 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 s E = 0.004±0.014±0.013 at 〈Q 2〉 = 0.077 GeV/c^2 , and G s E +0.09G s M = 0.004±0.011±0.005 at 〈Q 2〉 = 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.
PACS.25.30.Bf Elastic electron scattering 12.15.-y Electroweak interactions 11.30.Er Charge conjugation, parity, time reversal, and other discrete symmetries 14.20.Dh Protons and neutrons
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