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Polarization Transfer in Wide-Angle Compton Scattering and Single-Pion Photoproduction from the Proton
Fanelli, C. Salme, G. Cisbani, E. Kelleher, A. Meziane, M. Pentchev, L. Perdrisat, C. F.
Fanelli, C.
Salme, G.
Cisbani, E.
Kelleher, A.
Meziane, M.
Pentchev, L.
Perdrisat, C. F.
Abstract
Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of theta(p)(cm) cm = 70 degrees. The longitudinal transfer K-LL, measured to be 0.645 +/- 0.059 +/- 0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton. However, the observed value is similar to 3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude.
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2015-01-01
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Physics
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https://doi.org/10.1103/PhysRevLett.115.152001