2021/03/31 by G. N. Grauvogel, T. Kutz, A. Schmidt
Physics and Astronomy · #Atomic and Subatomic Physics Research #Electron #Hadron #Momentum transfer #Neutron #Positron #Quantum Chromodynamics and Particle Interactions #Quantum and Classical Electrodynamics #Radiative transfer #Range (aeronautics) #Scattering #Spin (aerodynamics) #nucl-ex
paper · pdf · doi:10.1140/epja/s10050-021-00531-7
published as Eur.Phys.J.A 57 (2021) 6, 213 · 7 pages, 4 figures. arXiv admin note: substantial text overlap with arXiv:2007.15081
openalex created_date 2021/03/15 · openalex publication_date 2021/06/01 · arxiv created 2021/07/12 · arxiv updated 2021/07/13 · openalex updated_date 2026/08/05
Two-photon exchange and the larger class of hadronic box diagrams are difficult to calculate without a large degree of model-dependence. At the same time, these processes are significant radiative corrections in parity-violating electron scattering, in neutron decay, and may even be responsible for the proton's form factor ratio discrepancy. New kinds of experimental data are needed to help constrain models and guide future box-diagram calculations. The target-normal single spin asymmetry, An, formed with an unpolarized beam scattering from a target that is polarized normal to the scattering plane, is sensitive to the imaginary part of the two-photon exchange amplitude, and can provide a valuable constraint. A measurement with both electrons and positrons can reduce sources of experimental error, and distinguish between the effects of two-photon exchange and those of time-reversal symmetry violation. This article describes a proposed experiment in Hall A, using the new Super Big-Bite Spectrometer that can cover a momentum transfer range in the critical zone of uncertainty between where hadronic calculations and those based on partonic degrees of freedom are expected to be accurate.