Speaker
Jan Bernauer
(MIT)
Description
One of the puzzles of the proton form factor is the difference between
determinations of the form factor ratio using unpolarized and polarized
beams. The causal source of this discrepancy is is believed to be two
photon exchange (TPE). Recent precision experiments at $Q^2$ below 2.5
$(\mathrm{GeV}/c)^2$ found smaller than expected but clear indication of two photon
exchange. However, they could not establish that TPE is indeed the bulk
effect driving the discrepancy at larger $Q^2$. This hampers our ability
to provide accurate, separated form factors are large $Q^2$, related to
the short-range structure of the proton. A multi-GeV positron beam
enables a new generation of experiments to study this effect in detail
at these larger $Q^2$. In my talk I will discuss the possible reach of
experiments at Jefferson Lab using unpolarized positron beams to measure
TPE directly.
Primary author
Jan Bernauer
(MIT)
