Title: Electromagnetic Single-nucleon Response involving Polarized Targets Show Chinese title

Title: 涉及极化靶的电磁单核子响应

Abstract: This work is an extension of our past study focused on a covariant representation of the electromagnetic (EM) current of spin-1/2 Dirac particles, specifically, nucleons. In the past study the EM responses that occur in unpolarized electron scattering from unpolarized nucleons were derived; however, scattering of polarized electrons from polarized nucleons was beyond the scope of that earlier work. Here such extensions are studied in detail. While in other work the EM response has already been developed for the double-polarization scattering problem, that effort was focused on high-energy collider physics. In the present study the formalism is recast into a set of EM response functions that have transparent dependencies on the relevant kinematic variables, especially on how these behave with respect to the momentum p of the (moving) struck, polarized nucleon. The motivation for such a reformulation of the problem is the desire to see a clear path to expansions in $p$ of the EM response for use in devising ``prescriptions for nuclear physics''. Results are provided where comparisons of the full (unexpanded) responses with various approximations that are frequently employed in studies of EM nuclear physics are made, demonstrating that under some circumstances such approximations are reasonable, whereas in other circumstances the expanded results are likely to be invalid. In addition, the EM current operators and approximations to them are discussed in detail. Show Chinese abstract

Abstract: 这项工作是对我们过去研究的延伸，该研究专注于自旋为 1/2 的狄拉克粒子（即核子）电磁（EM）流的协变表示。 在过去的研究中，导出了发生在非极化电子与非极化核子散射中的电磁响应；然而，极化电子与极化核子的散射超出了早期工作的范围。 在这里，这些扩展被详细研究。 虽然在其他工作中，电磁响应已经为双极化散射问题构建好了，但那个努力的重点是高能对撞机物理。 在本研究中，形式主义被重新表述为一组电磁响应函数，这些函数对相关运动学变量（特别是它们如何随被击中、极化的核子动量 p 的变化）具有透明的依赖性。 重新表述这个问题的动机是为了清楚地看到在电磁响应的 $p$ 扩展中找到一条清晰路径，以便用于制定“核物理处方”。 提供了结果，其中对完整的（未展开的）响应与经常用于电磁核物理研究的各种近似进行了比较，表明在某些情况下这些近似是合理的，而在其他情况下，展开的结果可能是无效的。 此外，详细讨论了电磁流算符及其近似值。