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Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2) |
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| Authors: | Maas F E Achenbach P Aulenbacher K Baunack S Capozza L Diefenbach J Grimm K Imai Y Hammel T von Harrach D Kabuss E M Kothe R Lee J H Lorente A Lopes Ginja A Nungesser L Schilling E Stephan G Weinrich C Altarev I Arvieux J Collin B Frascaria R Guidal M Kunne R Marchand D Morlet M Ong S van de Wiele J Kowalski S Plaster B Suleiman R Taylor S |
| Institution: | Institut für Kernphysik, Johannes Gutenberg Universit?t Mainz, J. J. Becherweg 45, D-55099 Mainz, Germany. |
| Abstract: | We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028. |
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