We look for asymmetries in the angular distributions of events from recent
data on $e^+ +e^-\\to p +\\bar p +\\gamma$ from BABAR collaboration.
From first principles, as the C-invariance of the electromagnetic interaction
and the crossing symmetry, the presence of two-photon exchange would
create a forward backward asymmetry in the data. The analysis of the
available data shows no asymmetry, within an error of 2\\%. This result
is consistent with a structureless model for the proton, based on a calculation of
$e^+ +e^-\\to \\mu^+ + \\mu^- +\\gamma$ with a proper replacement
of the muon mass. As no systematic deviations are seen, we can conclude
that these data do not give any hint of the presence of the two photon
contribution, in all the considered kinematical range. |
