通过 OLYMPUS 实验测量电荷平均的轻子-质子弹性散射截面
Measurement of the Charge-Averaged Elastic Lepton-Proton Scattering Cross Section by the OLYMPUS Experiment
AI总结：
OLYMPUS 利用电子与正电子束在氢靶上的弹性散射首次测量电荷平均截面，以抑制硬双光子交换效应并约束质子电磁形状因子。
摘要：
我们报告了对电子-质子与正电子-质子弹性散射截面平均值的首次测量。这种轻子电荷平均截面对硬双光子交换的主导效应不敏感，从而能够更可靠地获取质子的电磁形状因子。该截面提取自 OLYMPUS 实验在 DESY 获取的数据；实验中，交替储存的电子束和正电子束从无窗气体氢靶上发生散射。通过在大接收度环形谱仪中对散射轻子和反冲质子进行符合探测，识别出弹性散射事件。亮度则由前向电磁量能器中的 Møller、Bhabha 和弹性散射事例率确定。这些数据对现有的形状因子全局拟合具有一定的区分能力，并将为未来的拟合提供有价值的约束。
英文摘要：
We report the first measurement of the average of the electron-proton and positron-proton elastic scattering cross sections. This lepton charge-averaged cross section is insensitive to the leading effects of hard two-photon exchange, giving more robust access to the proton's electromagnetic form factors. The cross section was extracted from data taken by the OLYMPUS experiment at DESY, in which alternating stored electron and positron beams were scattered from a windowless gaseous hydrogen target. Elastic scattering events were identified from the coincident detection of the scattered lepton and recoil proton in a large-acceptance toroidal spectrometer. The luminosity was determined from the rates of Møller, Bhabha and elastic scattering in forward electromagnetic calorimeters. The data provide some selectivity between existing form factor global fits and will provide valuable constraints to future fits.
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