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, \(A_n\), 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.

如果没有高度的模型依赖性，双光子交换和更大类别的强子箱形图很难计算。同时，这些过程在违反奇偶校验的电子散射、中子衰变中是重要的辐射校正，甚至可能是质子形状因数比差异的原因。需要新的实验数据来帮助约束模型和指导未来的箱形图计算。目标法向单自旋不对称性，\(A_n\)，由来自目标的非偏振光束散射形成，该光束垂直于散射平面偏振，对双光子交换幅度的虚部敏感，可以提供有价值的约束。使用电子和正电子的测量可以减少实验误差的来源，并区分双光子交换的影响和时间反转对称性破坏的影响。本文描述了在 A 厅进行的一项拟议实验，使用新的超级大咬合光谱仪，该光谱仪可以覆盖强子计算与基于分子自由度的计算预计准确的关键不确定区域中的动量传递范围。