Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment
Creators: name: Henderson, Brian
name: Ice, Lauren
name: Khaneft, Dmitry
name: O'Connor, Colton
name: Russell, Rebecca
name: Schmidt, Axel
name: Bernauer, Jan
name: Kohl, Michael
name: Akopov, Norair
name: Alarcon, Ricardo
name: Ates, Ozgur
name: Avetisyan, Albert
name: Beck, Reinhard
name: Belostotski, Stanislav
name: Bessuille, Jason
name: Brinker, Frank
name: Calarco, John
name: Carassiti, V.
name: Cisbani, E.
name: Ciullo, G.
name: Contalbrigo, Marco
name: De Leo, R.
name: Diefenbach, Juergen
name: Donnelly, T. W.
name: Dow, Karen
name: Elbakian, G.
name: Eversheim, P. D.
name: Frullani, Salvatore
name: Funke, Christian
name: Gavrilov, Gennady
name: Gläser, B.
name: Goerrissen, Nico
name: Hasell, Douglas
name: Hauschildt, Jan
name: Hoffmeister, Philipp
name: Holler, Yorck
name: Ihloff, E.
name: Izotov, Anton
name: Kaiser, Ralf
name: Karyan, Gevorg
name: Kelsey, James
name: Kiselev, Alexander
name: Klassen, Peter
name: Krivshich, A.
name: Lehmann, Inti
name: Lenisa, Paolo
name: Lenz, Dennis
name: Lumsden, S.
name: Ma, Yue
name: Maas, Frank
name: Marukyan, Hrachya
name: Miklukho, Oleg
name: Milner, Richard
name: Movsisyan, Aram
name: Murray, Morgan
name: Naryshkine, Iouri
name: Perez Benito, R.
name: Perrino, R.
name: Redwine, Robert
name: Rodriguez Pineiro, David
name: Rosner, G.
name: Schneekloth, Uwe
name: Seitz, B.
name: Statera, M.
name: Thiel, A.
name: Vardanyan, Henrik
name: Veretennikov, Denis
name: Vidal, C.
name: Winnebeck, Alexander
name: Yeganov, Vladislav
Publisher: name: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Year: 2016
Subjects: subject: 550

description: 4(2016). doi:10.3204/PUBDB-2016-05585
description: 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 &lt; $\epsilon$&lt; 0:978, are smaller than hadronic two-photon exchange calculations predict, but are consistent with phenomenological models.
description: Published by APS, College Park, Md.