Polarization transfer in $$\varvec{e}^+p \rightarrow e^+ \varvec{p}$$ scattering using the Super BigBite Spectrometer
Polarization transfer in $$\varvec{e}^+p \rightarrow e^+ \varvec{p}$$ scattering using the Super BigBite Spectrometer
复制标题
使用 Super BigBite 光谱仪进行 $$varvec{e}^ p ightarrow e^ varvec{p}$$ 散射中的偏振传输
DOI：
10.1140/epja/s10050-021-00509-5
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Schmidt, A.
中科院分区：
文献类型：
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作者：
Puckett, A. J.;Bernauer, J. C.;Schmidt, A.
多光子交换和其他高阶QED修正对弹性电子-质子散射的影响一直是实验和理论上高度关注的课题，因为大动量转移质子电磁形状因子比的偏振转移测量最终确定了该比率随时间的强烈下降。这一结果与先前使用Rosenbluth分离技术从横截面测量中提取该量不一致。通过非偏振截面比提取双光子交换（TPE）效应已成为实验研究的重点，但偏振弹性散射中的偏振转移也能揭示硬双光子交换的证据。此外，它对广义TPE形状因子具有不同的灵敏度，这意味着测量提供了无法单独从非偏振散射中收集的新信息。固定极化转移的依赖性以及电子-质子和正电子-质子散射之间的偏差是硬TPE的关键特征。杰斐逊实验室的极化正电子束将为首次测量正电子极化转移提供一个独特的机会，与电子散射数据的比较将对硬TPE产生有价值的限制。在这里，我们提出了一个测量方案，在大厅A，结合超级BigBite光谱仪测量反冲质子极化，与非磁性量热探测器触发弹性散射的正电子。虽然正电子束的束流减少将限制运动学范围，但这种测量将具有非常小的系统不确定性，使其成为TPE的清洁探针。
The effects of multi-photon-exchange and other higher-order QED corrections on elastic electron-proton scattering have been a subject of high experimental and theoretical interest since the polarization transfer measurements of the proton electromagnetic form factor ratioat large momentum transferconclusively established the strong decrease of this ratio withfor. This result is incompatible with previous extractions of this quantity from cross section measurements using the Rosenbluth Separation technique. Much experimental attention has been focused on extracting the two-photon exchange (TPE) effect through the unpolarizedcross section ratio, but polarization transfer in polarized elastic scattering can also reveal evidence of hard two-photon exchange. Furthermore, it has a different sensitivity to the generalized TPE form factors, meaning that measurements provide new information that cannot be gleaned from unpolarized scattering alone. Both-dependence of polarization transfer at fixed, and deviations between electron-proton and positron-proton scattering are key signatures of hard TPE. A polarized positron beam at Jefferson Lab would present a unique opportunity to make the first measurement of positron polarization transfer, and comparison with electron-scattering data would place valuable constraints on hard TPE. Here, we propose a measurement program in Hall A that combines the Super BigBite Spectrometer for measuring recoil proton polarization, with a non-magnetic calorimetric detector for triggering on elastically scattered positrons. Though the reduced beam current of the positron beam will restrict the kinematic reach, this measurement will have very small systematic uncertainties, making it a clean probe of TPE.