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DESCRIPTION:Dipak Rimal\, Florida International University\n\nThe electroma
gnetic form factors of the proton are extracted by analyzing unpolarized a
nd polarized electron scattering data assuming the Born approximation. The
extracted ratios of electric to magnetic form factors (GE/GM) by the two methods show a significant discrepancy that increase
s with Q2. One possible explanation for the\nobserved discrepan
cy is the contribution from two-photon exchange (TPE) effects\, which are
not generally accounted for in the standard treatment of radiative correc
tions. Theoretical calculations estimating the magnitude of the TPE effect
are highly model-dependent and limited experimental evidence for such ef
fect exists. The ratio of positron-proton to electron-proton elastic scatt
ering cross sections (R = σ\;(e+ p)/σ\;(e- p)) provides a model-independent measurement of the TPE e
ffect. One such measurement of R was performed by using a mixed electron-
positron beam at Jefferson Lab Hall B. Both electrons and positrons were
elastically scattered from a 30-cm-long liquid hydrogen target. The result
ing scattered particles were detected in CLAS. The elastic events were the
n identified by using elastic scattering kinematics. The measurement cover
s a\nrange of Q2 < 2 GeV2 and 0:1 < ε\; < 1. In
the kinematics of the experiment\, our results are consistent with the had
ronic calculation of the TPE effect by Blunden\, Melnitchouk\, and Tjon.
The details of the CLAS TPE experiment and the results will be discussed.
DTSTART:20140415T193000Z
LOCATION:Physics Building\, Room 204
SUMMARY:Proton Form Factor Puzzle and the CLAS Two-Photon Exchange Experime
nt
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