Search for Effects Beyond the Born Approximation in Polarization Transfer Observables in (e)over-right-arrow p Elastic Scattering
Physical Review Letters
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) over right arrow, e' (p) over right arrow) reaction for three different beam energies at a Q(2) = 2: 5 GeV2, spanning a wide range of the kinematic parameter epsilon. The ratio R, which equals mu(p)G(E)/G(M) in the Born approximation, is found to be independent of epsilon at the 1.5% level. The epsilon dependence of the longitudinal polarization transfer component P-l shows an enhancement of (2.3 +/- 0.6)% relative to the Born approximation at large epsilon
Meziane, M.; Pentchev, L.; Perdrisat, C. F.; Brash, E. J.; Carter, P.; and Jensen, E., Search for Effects Beyond the Born Approximation in Polarization Transfer Observables in (e)over-right-arrow p Elastic Scattering (2011). Physical Review Letters, 106(13).