Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2).
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.
Institut für Kernphysik, Johannes Gutenberg Universität Mainz, J. J. Becherweg 45, D-55099 Mainz, Germany.
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Maas
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Achenbach
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Aulenbacher
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Baunack
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Capozza
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Diefenbach
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Grimm
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Imai
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Hammel
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von Harrach
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Kabuss
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Kothe
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Lee
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Lorente
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Lopes Ginja
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Nungesser
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Schilling
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Stephan
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Weinrich
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Altarev
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Arvieux
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Collin
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Frascaria
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Guidal
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Kunne
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Marchand
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Morlet
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Ong
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van de Wiele
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Kowalski
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Plaster
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Suleiman
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Taylor