Search for Effects Beyond the Born Approximation in Polarization Transfer Observables in ep Elastic Scattering

摘要

Intensive theoretical and experimental efforts over the past decade have aimed at explaining the discrepancy between data for the proton electric to magnetic form factor ratio, G_E/G_M, obtained separately from cross section and polarization transfer measurements. One possible explanation for this difference is a two-photon-exchange contribution. In an effort to search for effects beyond the one-photon-exchange or Born approximation, we report measurements of polarization transfer observables in the elastic H(e, e'p) reaction for three different beam energies at a Q~2 = 2.5 GeV~2, spanning a wide range of the kinematic parameter e. The ratio R, which equals 靇pG_E/G_M in the Born approximation, is found to be independent of e at the 1.5% level. The e dependence of the longitudinal polarization transfer component P_e shows an enhancement of (2.3