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DOE OSTI · 1980790

Two photon exchange with nuclei from $e^+/e^-$ elastic cross section ratios

Kutz, T.·Schmidt, A.
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Abstract

Hadronic box diagrams pose a significant source of radiative corrections to lepton scattering and β -decay measurements, yet their calculation remains highly model-dependent. Two-photon exchange is a box diagram generally relevant to most lepton scattering experiments, and is directly detectable via multiple observables. Single-spin asymmetries (SSA) are sensitive to the imaginary part of the TPE amplitude, while the ratio of $e^+/e^-$ elastic scattering cross sections is sensitive to the real part of the TPE amplitude. While SSA measurements have been reported for several complex nuclei, measurements of the $e^+/e^-$ ratio exist only for the proton. Proposed here is a measurement of the $e^+/e^-$ ratio on 4 He, a feasible nuclear target for which the ratio’s deviation from unity due to TPE is expected to be on order of 1–2%. Choosing a low Z nucleus minimizes Coulomb distortions, which could greatly overwhelm TPE for heavier nuclei. The proposed 19-day program, including measurements at three kinematic settings between 0.3 < Q 2 < 0.4 GeV 2 , would be made possible by the addition of a positron source at Jefferson Lab.

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71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS

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Kutz, T., Schmidt, A.. 2022-02-28. Two photon exchange with nuclei from $e^+/e^-$ elastic cross section ratios. https://doi.org/10.1140/epja%2Fs10050-022-00682-1

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