%0 Electronic Article
%A Henderson, Brian
%A Ice, Lauren
%A Khaneft, Dmitry
%A O'Connor, Colton
%A Russell, Rebecca
%A Schmidt, Axel
%A Bernauer, Jan
%A Kohl, Michael
%A Akopov, Norair
%A Alarcon, Ricardo
%A Ates, Ozgur
%A Avetisyan, Albert
%A Beck, Reinhard
%A Belostotski, Stanislav
%A Bessuille, Jason
%A Brinker, Frank
%A Calarco, John
%A Carassiti, V.
%A Cisbani, E.
%A Ciullo, G.
%A Contalbrigo, Marco
%A De Leo, R.
%A Diefenbach, Juergen
%A Donnelly, T. W.
%A Dow, Karen
%A Elbakian, G.
%A Eversheim, P. D.
%A Frullani, Salvatore
%A Funke, Christian
%A Gavrilov, Gennady
%A Gläser, B.
%A Goerrissen, Nico
%A Hasell, Douglas
%A Hauschildt, Jan
%A Hoffmeister, Philipp
%A Holler, Yorck
%A Ihloff, E.
%A Izotov, Anton
%A Kaiser, Ralf
%A Karyan, Gevorg
%A Kelsey, James
%A Kiselev, Alexander
%A Klassen, Peter
%A Krivshich, A.
%A Lehmann, Inti
%A Lenisa, Paolo
%A Lenz, Dennis
%A Lumsden, S.
%A Ma, Yue
%A Maas, Frank
%A Marukyan, Hrachya
%A Miklukho, Oleg
%A Milner, Richard
%A Movsisyan, Aram
%A Murray, Morgan
%A Naryshkine, Iouri
%A Perez Benito, R.
%A Perrino, R.
%A Redwine, Robert
%A Rodriguez Pineiro, David
%A Rosner, G.
%A Schneekloth, Uwe
%A Seitz, B.
%A Statera, M.
%A Thiel, A.
%A Vardanyan, Henrik
%A Veretennikov, Denis
%A Vidal, C.
%A Winnebeck, Alexander
%A Yeganov, Vladislav
%T Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment
%N DESY-16-217
%@ 0031-9007
%C College Park, Md.
%I APS
%M PUBDB-2016-05585
%M DESY-16-217
%M arXiv:1611.04685
%P 4
%D 2016
%X The OLYMPUS collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, <i>R</i><sub>2 γ</sub>, 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  ≈  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<sup>−1</sup> was collected. In the extraction of <i>R</i><sub>2γ</sub>, 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 <i>R</i><sub>2γ</sub>, presented here for a wide range of virtual photon polarization 0:456 < ϵ< 0:978, are smaller than hadronic two-photon exchange calculations predict, but are consistent with phenomenological models.
%F PUB:(DE-HGF)25 ; PUB:(DE-HGF)29
%9 PreprintReport
%R 10.3204/PUBDB-2016-05585
%U https://bib-pubdb1.desy.de/record/315050