Polarization Transfer in Wide-Angle Compton Scattering and Single-Pion Photoproduction from the Proton

C. Fanelli et al.
Phys. Rev. Lett. 115, 152001 – Published 6 October 2015

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 θcmp=70°. The longitudinal transfer KLL, 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 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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  • Received 22 June 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.152001

© 2015 American Physical Society

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Vol. 115, Iss. 15 — 9 October 2015

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