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| Home > Publications database > Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment |
| Report/Journal Article | PUBDB-2016-05579 |
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2017
APS
College Park, Md.
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Please use a persistent id in citations: doi:10.1103/PhysRevLett.118.092501 doi:10.3204/PUBDB-2016-05585
Report No.: DESY-16-217; arXiv:1611.04685
Abstract: The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, $\it R_{2 \gamma}$, a direct measure of the contribution of hard two-photon exchange to the elastic cross section. In the OLYMPUS measurement, 2.01 GeV electron and positron beams were directed through a hydrogen gas target internal to the DORIS storage ring at DESY. A toroidal magnetic spectrometer instrumented with drift chambers and time-of-flight scintillators detected elastically scattered leptons in coincidence with recoiling protons over a scattering angle range of $\approx$ 20° to 80°. The relative luminosity between the two beam species was monitored using tracking telescopes of interleaved GEM and MWPC detectors at 12°, as well as symmetric Møller/Bhabha calorimeters at 1:29°. A total integrated luminosity of $4.5 fb^{-1}$ was collected. In the extraction of $\it R_{2\gamma}$, radiative effects were taken into account using a Monte Carlo generator to simulate the convolutions of internal bremsstrahlung with experiment-specific conditions such as detector acceptance and reconstruction efficiency. The resulting values of $\it R_{2\gamma}$, presented here for a wide range of virtual photon polarization 0:456 < $\epsilon$< 0:978, are smaller than hadronic two-photon exchange calculations predict, but are consistent with phenomenological models.
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Preprint/Report
Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment
College Park, Md. : APS 4 pp. (2016) [10.3204/PUBDB-2016-05585]
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