The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P ℓ , the transverse and longitudinal recoil proton polarization components, respectively, for the elastic ep → e p reaction in the four-momentum transfer squared range of 0.5 to 3.5 GeV 2 . In the single-photon exchange approximation, the ratio GEp/GMp is directly proportional to the ratio Pt/P ℓ . The simultaneous measurement of Pt and P ℓ in a polarimeter reduces systematic uncertainties. The results for the ratio GEp/GMp show a systematic decrease with increasing Q 2 , indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been re-analyzed and systematic uncertainties have become significantly smaller than previously published results.

Cross-section values for Compton scattering on the proton were measured at 25 kinematic settings over the range s=5-11 and -t=2-7 GeV2 with a statistical accuracy of a few percent. The scaling power for the s dependence of the cross section at fixed center-of-mass angle was found to be 8.0+/-0.2, strongly inconsistent with the prediction of perturbative QCD. The observed cross-section values are in fair agreement with the calculations using the handbag mechanism, in which the external photons couple to a single quark.

Exclusive electroproduction of 0 mesons on protons in the backward hemisphere has been studied at Q 2 = 1.0 GeV 2 by detecting protons in the forward direction in coincidence with scattered electrons from the 4 GeV electron beam in Jefferson Lab's Hall A. The data span the range of the total ͑␥ * p͒ center-of-mass energy W from the pion production threshold to W = 2.0 GeV. The differential cross sections T + ⑀ L , TL , and TT were separated from the azimuthal distribution and are presented together with the MAID and SAID parametrizations.

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