Speaker
Axel Schmidt
(MIT)
Description
The discrepancy between polarized and unpolarized measurements of the proton's electromagnetic form factors is striking, and suggests that two-photon exchange (TPE) may be playing a larger role in elastic electron-proton scattering than is estimated in standard radiative corrections formulae. While TPE is difficult to calculate in a model-independent way, it can be determined experimentally from asymmetries between electron-proton and positron-proton scattering. The possibility of a polarized positron beam at Jefferson Lab would open the door to measurements of TPE using polarization observables. The epsilon-dependence of polarization-transfer to the proton is an excellent test of our understanding of TPE in the context of electron-proton radiative corrections, and the ability to form a "super-asymmetry" between electrons and positrons would lead to a
drastic reduction of systematics. In addition, a measurement of the target single-spin asymmetry, which is sensitive to the imaginary part of the TPE amplitude, can be improved through the simultaneous measurement with electron and positron beams. In this talk, I will discuss the prospects and limitations for future measurements at Jefferson Lab.
Primary author
Axel Schmidt
(MIT)
