Measurement of the transverse beam spin asymmetry in elastic electron-proton scattering and the inelastic contribution to the imaginary part of the two-photon exchange amplitude.
We report on a measurement of the asymmetry in the scattering of transversely polarized electrons off unpolarized protons, A( perpendicular), at two Q2 values of 0.106 and 0.230 (GeV/c)(2) and a scattering angle of 30 degrees <theta(e)<40 degrees . The measured transverse asymmetries are A( perpendicular)(Q(2)=0.106 (GeV/c)(2))=(-8.59+/-0.89(stat)+/-0.75(syst))x10(-6) and A( perpendicular)(Q(2)=0.230 (GeV/c)(2))=(-8.52+/-2.31(stat)+/-0.87(syst))x10(-6). The first errors denote the statistical error and the second the systematic uncertainties. From comparison with theoretical estimates of A( perpendicular) we conclude that piN-intermediate states give a substantial contribution to the imaginary part of the two-photon amplitude. There is no obvious reason why this should be different for the real part of the two-photon amplitude, which enters into the radiative corrections for the Rosenbluth separation measurements of the electric form factor of the proton.
Maas
F E
FE
Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, J.-J.-Becherweg 45, D-55099 Mainz, Germany. maas@kph.uni-mainz.de
Aulenbacher
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Baunack
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Capozza
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Diefenbach
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Gläser
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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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Sanchez-Lorente
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Schilling
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Schwaab
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Stephan
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Weber
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Weinrich
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Altarev
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Arvieux
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Elyakoubi
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Frascaria
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Kunne
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Morlet
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Ong
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Vandewiele
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Kowalski
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Suleiman
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Taylor
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