Two-Photon Exchange Effects in Elastic Electron-Proton Scattering

Thesis/Dissertation · Thu Aug 01 00:00:00 EDT 2013

DOI:https://doi.org/10.2172/1093450· OSTI ID:1093450

Johnson, Myriam James ^[1]

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1. Argonne National Lab. (ANL), Argonne, IL (United States)

Two methods, Rosenbluth separation and polarization transfer, can be used to extract the proton form factor ratio μp G_Ep/G_Mp, 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.

• Research Organization: Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1093450
• Report Number(s): JLAB-PHY-13-1795; DOE/OR/23177-2774
• Resource Relation: Related Information: JLAB EXP-05-017
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS