Two photon exchange with nuclei from $e^+/e^-$ elastic cross section ratios
- Massachusetts Institute of Technology (MIT), Cambridge, MA (United States); George Washington University, Washington, DC (United States); OSTI
- George Washington University, Washington, DC (United States)
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 < Q2 < 0.4 GeV2, would be made possible by the addition of a positron source at Jefferson Lab.
- Research Organization:
- George Washington University, Washington, DC (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- Grant/Contract Number:
- SC0016583
- OSTI ID:
- 1980790
- Journal Information:
- European Physical Journal. A, Journal Name: European Physical Journal. A Journal Issue: 3 Vol. 58; ISSN 1434-6001
- Publisher:
- SpringerCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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