The first measurements of elastic electron nucleon scattering with polarization transfer, allowing to separate the electric and magnetic nucleon form factors, showed a significant discrepancy with Rosenbluth measurement of the cross section of the same process. The two-photon exchange, suspected to be the cause of this observation, got a major focus since then. The two-photon exchange is...
The beam-normal spin asymmetry from polarized positron scattering is investigated in the energy regime 1−150 MeV by means of the phase-shift analysis. The nonperturbative consideration of QED effects leads to spin-asymmetry changes of a few percent irrespective of the target nucleus. Corrections from low-lying transient nuclear excitations depend strongly on the collision geometry and the...
The longest-range weak pion-nucleon coupling constant, h_π^1, is important for nuclear parity violation. Prospects of a new measurement of h_π^1 in a theoretically clean process are presented. A measurement of the parity-violating asymmetry in pion photoproduction off the proton is related to h_π^1 in a low-energy theorem of the photon polarization asymmetry at threshold in the chiral limit. A...
