OLYMPUS and TREK: Two Precision Experiments to Determine the Two-Photon Exchange Effect in Lepton-Proton Scattering and to Search for New Physics Beyond the Standard Model

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。在RosenBluth和反冲偏振法之间观测到的质子电磁形状因数比的差异被解释为由于以前忽略的双光子交换(TPE)的影响。TPE的证据可以通过正电子-质子和电子-质子弹性截面的比较直接和最严格地检验，因为它们的差异与TPE的幅度成正比。在没有明确的实验测试的情况下，不仅电磁形状因子，而且通常在单光子交换框架下进行的所有电子散射数据的解释都受到了相当大的质疑。德国汉堡DESY的奥林巴斯实验被提议通过精确测量正电子-质子与电子-质子弹性未极化截面的比率来确定双光子交换在弹性轻子-质子散射中的作用。它利用存储环Doris上的强正电子束和来自MIT-Bates直线加速器中心的爆炸探测器。Doris是一个内部未极化的氢气靶。该设施将增加基于气体电子倍增器(GEM)技术的前角跟踪望远镜，用作光度监测器，将在汉普顿大学建造。预计新的宝石探测器的开发将在杰斐逊实验室和日本J-PARC的未来实验中应用。所提出的研究计划为国内外一流的教育和研究目的提供了巨大的机会。这项提议将在汉普顿大学的校园内建立一个新的实验室，并为少数族裔学生，主要是非洲裔美国人的学生提供新的研究和教育机会。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The observed discrepancy in measurements of the proton electric-to-magnetic form factor ratio between the Rosenbluth and recoil polarization method has been interpreted as due to previously neglected effects of two-photon exchange (TPE). Evidence for TPE can be directly and most stringently tested by comparison of positron-proton and electron-proton elastic cross sections, as their difference is proportional to the TPE amplitude. Without a definitive experimental test, not only the electromagnetic form factors but also the interpretations of all electron scattering data, usually done in the framework of single-photon exchange, are under considerable doubt.The OLYMPUS experiment at DESY, Hamburg, Germany has been proposed to definitively determine the effect of two-photon exchange in elastic lepton-proton scattering by precisely measuring the ratio of positron-proton to electron-proton elastic unpolarized cross sections. It makes use of intense beams of positrons and electrons at the storage ring DORIS, an internal unpolarized hydrogen gas target, and the BLAST detector from the MIT-Bates Linear Accelerator Center. The setup will be augmented with forward-angle tracking telescopes based on gas electron multiplier (GEM) technology, to be used as luminosity monitors, which will be constructed at Hampton University. It is anticipated that development of new GEM detectors will be applicable in future experiments at Jefferson Lab and at J-PARC in Japan.The proposed research program offers great opportunity for first class education and research purpose domestically and abroad. This proposal will lead to a new lab on the campus of Hampton University and opens new research and educational opportunities for students from minority populations, predominantly African-Americans.