Two-Photon Exchange E#27;ffects in Elastic Electron-Proton Scattering Page: 3 of 89
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ABSTRACT
Two-Photon Exchange Effects in Elastic Electron-Proton Scattering
Myriam James Johnson
Two methods, Rosenbluth separation and polarization transfer, can be used to extract
the proton form factor ratio pPGEp/Gmp, but they do not yield the same results. It is
thought that the disagreement is due to two photon exchange corrections to the differential
cross sections. High precision proton Rosenbluth extractions were carried out at 102
kinematics points spanning 16 values of momentum transfer Q2, from 0.40 to 5.76 GeV2.
Reduced cross sections were found to 1.1% or better for Q2 less than 3 GeV2, increasing to
4% at 5.76 GeV2. The form factor ratios were determined to 1.5-3% for Q2 < 1.5 GeV2,
increasing to 9% by 3 GeV2 and rapidly above. Our data agrees with prior Rosenbluth,
improving upon it the 1.0 - 2.0 GeV2 range to conclusively show a separation from
polarization transfer where it had not been certain before. In addition, reduced cross
sections at each Q2 were tested for nonlinearity in the angular variable. Such a departure
from linearity would be a signature of two photon exchange effects, and prior data had not
been sufficiently precise to show nonzero curvature. Our data begins to hint at negative
curvature but does not yet show a significant departure from zero.
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Laboratory, Argonne National. Two-Photon Exchange E#27;ffects in Elastic Electron-Proton Scattering, thesis or dissertation, August 1, 2013; Newport News, Virginia. (https://digital.library.unt.edu/ark:/67531/metadc832092/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.