TY  - JOUR
AU  - Henderson, Brian
AU  - Ice, Lauren
AU  - Khaneft, Dmitry
AU  - O'Connor, Colton
AU  - Russell, Rebecca
AU  - Schmidt, Axel
AU  - Bernauer, Jan
AU  - Kohl, Michael
AU  - Akopov, Norair
AU  - Alarcon, Ricardo
AU  - Ates, Ozgur
AU  - Avetisyan, Albert
AU  - Beck, Reinhard
AU  - Belostotski, Stanislav
AU  - Bessuille, Jason
AU  - Brinker, Frank
AU  - Calarco, John
AU  - Carassiti, V.
AU  - Cisbani, E.
AU  - Ciullo, G.
AU  - Contalbrigo, Marco
AU  - De Leo, R.
AU  - Diefenbach, Juergen
AU  - Donnelly, T. W.
AU  - Dow, Karen
AU  - Elbakian, G.
AU  - Eversheim, P. D.
AU  - Frullani, Salvatore
AU  - Funke, Christian
AU  - Gavrilov, Gennady
AU  - Gläser, B.
AU  - Goerrissen, Nico
AU  - Hasell, Douglas
AU  - Hauschildt, Jan
AU  - Hoffmeister, Philipp
AU  - Holler, Yorck
AU  - Ihloff, E.
AU  - Izotov, Anton
AU  - Kaiser, Ralf
AU  - Karyan, Gevorg
AU  - Kelsey, James
AU  - Kiselev, Alexander
AU  - Klassen, Peter
AU  - Krivshich, A.
AU  - Lehmann, Inti
AU  - Lenisa, Paolo
AU  - Lenz, Dennis
AU  - Lumsden, S.
AU  - Ma, Yue
AU  - Maas, Frank
AU  - Marukyan, Hrachya
AU  - Miklukho, Oleg
AU  - Milner, Richard
AU  - Movsisyan, Aram
AU  - Murray, Morgan
AU  - Naryshkine, Iouri
AU  - Perez Benito, R.
AU  - Perrino, R.
AU  - Redwine, Robert
AU  - Rodriguez Pineiro, David
AU  - Rosner, G.
AU  - Schneekloth, Uwe
AU  - Seitz, B.
AU  - Statera, M.
AU  - Thiel, A.
AU  - Vardanyan, Henrik
AU  - Veretennikov, Denis
AU  - Vidal, C.
AU  - Winnebeck, Alexander
AU  - Yeganov, Vladislav
TI  - Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment
JO  - Physical review letters
VL  - 118
IS  - 9
SN  - 0031-9007
CY  - College Park, Md.
PB  - APS
M1  - PUBDB-2016-05579
M1  - DESY-16-217
M1  - arXiv:1611.04685
SP  - 092501 
PY  - 2017
AB  - 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.  
LB  - PUB:(DE-HGF)29 ; PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000396045900004
C6  - pmid:28306315
DO  - DOI:10.1103/PhysRevLett.118.092501
UR  - https://bib-pubdb1.desy.de/record/315044
ER  -