A high sensitivity search for a light U-boson by means of a positron beam incident on a hydrogen target is proposed. We described a concept of the experiment and two possible realizations. The projected result of this experiment corresponds to an upper limit on the square of coupling constant | f eU | 2 = 3 × 10 −9 with a signal to noise ratio of five.

Recent determinations of the proton electric to magnetic elastic form factor ratio from polarization transfer measurements at Jefferson Lab indicate an unexpected and dramatic discrepancy with the elastic form factor ratio obtained using the Rosenbluth separation technique in unpolarized cross section measurements. This discrepancy has been explained as the effect of twophoton exchange beyond the usual one-photon exchange approximation in the calculation of the elastic electron-proton scattering cross section. The OLYMPUS experiment at DESY, Hamburg, Germany has been proposed to definitively determine the effect of two-photon exchange in elastic lepton-proton scattering by precisely measuring the ratio of positron-proton to electron-proton elastic unpolarized cross sections.

A brief discussion of the DVCS program at the Jefferson Lab 12 GeV energy upgrade is given. Emphasis is on what can be learned from using both polarized electron and polarized positron beams in conjunction with polarized nucleon targets.Comment: 6 pages, 4 figures, invited talk at the Workshop on Positron beams JLab, Newport News, March, 200

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The Coulomb distortion effects have been for a long time neglected in deep inelastic scattering for the good reason that the incident energies were very high. But for energies in the range of earlier data from SLAC or at JLab, the Coulomb distortion could have the potential consequence of affecting the A-dependence of the EMC effect and of the longitudinal to transverse virtual photon absorption cross section ratio R(x, Q 2 ).