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.
