Updated analysis of recent results on electron and positron elastic scattering on the proton

Abstract

We discuss recent experimental results concerning the cross section ratio of positron over electron elastic scattering on protons, and compare with the predictions of a pre-existent calculation. The deviation from unity of this ratio, i.e., a charge asymmetry different from zero, is the signature of contributions beyond the Born approximation. After reviewing the published results, we compare the elastic data to a calculation which includes the diagram corresponding to two-photon exchange.It turns out that all the data on the cross section ratio, in the limit of their precision, do not show evidence of enhanced two-photon contribution beyond the expected percent level. Our results confirm that experimental evidence for a large contribution of two-photon exchange is not yet found.

Feasibility studies for the measurement of time-like proton electromagnetic form factors from $$\bar{p}p \rightarrow \mu ^+\mu ^-$$ at $$\overline{\text {P}}\text {ANDA}$$ at FAIR

“…The recent experiments from the OLYMPUS [10], CLAS [11] and VEPP [12] as well as the GEp2gamma [13] collaborations did not show evidence of a two photon exchange contribution at the level needed to explain the discrepancy (6% relative). A common analysis of these experiments shows that the difference between the cross sections of electron and positron elastic scattering on protons -when consistently corrected by radiative corrections -remains within the uncertainty of the radiative correction calculation [14].…”