Polarization Transfer in Proton Compton Scattering at High Momentum Transfer

Abstract

Compton scattering from the proton was investigated at $s=6.9\text{ }\text{ }{\mathrm{GeV}}^{2}$ and $t=\ensuremath{-}4.0\text{ }\text{ }{\mathrm{GeV}}^{2}$ via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in disagreement with a prediction of perturbative QCD based on a two-gluon exchange mechanism, but agree well with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton.