Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment

Henderson, Brian S.; Ice, Lauren; Khaneft, D.; O'Connor, Colton; Russell, Rebecca L.; Schmidt, Axel; Bernauer, J. C.; Köhl, M.; Акопов, Н.; Alarcón, R.; Ates, O.; Avetisyan, A.; Beck, R.; Belostotski, S.; Bessuille, J.; Brinker, Frank; Calarco, J. R.; Carassiti, V.; Cisbani, E.; Ciullo, G.; Contalbrigo, M.; Лео, Р. Де; Diefenbach, J.; Donnelly, T. W.; Dow, K.; Elbakian, G.; Eversheim, P.D.; Frullani, S.; Funke, Ch.; Gavrilov, G.; Gläser, B.; Görrissen, N.; Hasell, D.; Hauschildt, J.; Hoffmeister, P.; Holler, Y.; Ihloff, E.; Izotov, A.; Kaiser, R.; Karyan, G.; Kelsey, J.; Kiselev, A.; Klassen, P.; Krivshich, A.; Lehmann, I.; Lenisa, P.; Lenz, Dan; Lumsden, S.; Ma, Yue; Maas, F. E.; Marukyan, H.; Miklukho, O. V.; Milner, R.; Movsisyan, A.; Murray, M.; Naryshkin, Y.; Benito, R. Pérez; Perrino, R.; Redwine, R.; Piñeiro, D. Rodríguez; Rosner, G.; Schneekloth, U.; Seitz, B.; Statera, M.; Thiel, A.; Vardanyan, H.; Veretennikov, D.; Vidal, C.; Winnebeck, A.; Yeganov, V.

doi:10.1103/physrevlett.118.092501

Cited by 88 publications

(82 citation statements)

References 56 publications

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“…The main effect of the latter is to remove the discrepancy between values of G e (q) at very large q resulting from determinations via Rosenbluth separation and polarization transfer, respectively. For a recent review, see [11]; for experiments checking on the two-photon exchange, see [12][13][14].…”

Section: Electron Scatteringmentioning

confidence: 99%

Proton Charge Radius from Electron Scattering

Sick

2017

Atoms

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Abstract:The rms-radius R of the proton charge distribution is a fundamental quantity needed for precision physics. This radius, traditionally determined from elastic electron-proton scattering via the slope of the Sachs form factor G e (q 2 ) extrapolated to momentum transfer q 2 = 0, shows a large scatter. We discuss the approaches used to analyze the e-p data, partly redo these analyses in order to identify the sources of the discrepancies and explore alternative parameterizations. The problem lies in the model dependence of the parameterized G(q) needed for the extrapolation. This shape of G(q < q min ) is closely related to the shape of the charge density ρ(r) at large radii r, a quantity that is ignored in most analyses. When using our physics knowledge about this large-r density together with the information contained in the high-q data, the model dependence of the extrapolation is reduced, and different parameterizations of the pre-2010 data yield a consistent value for R = 0.887 ± 0.012 fm. This value disagrees with the more precise value 0.8409 ± 0.0004 fm determined from the Lamb shift in muonic hydrogen.

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Section: Electron Scatteringmentioning

confidence: 99%

Proton Charge Radius from Electron Scattering

Sick

2017

Atoms

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“…This method was used to determine the relative luminosity between electron and positron datasets in the OLYMPUS experiment [2] and achieved better accuracy than the method of comparing Møller and Bhabha rates alone. For the specific case of OLYMPUS, we estimate that the method is accurate to within 0.36% for a determination of the relative luminosities.…”

Section: Discussionmentioning

confidence: 99%

“…This uncertainty ranges from 0.04-0.13% over the OLYMPUS acceptance, and is quoted as the beam energy uncertainty for the OLYMPUS result [2]. Since beam energy uncertainty and luminosity uncertainty are treated as separate in the OLYMPUS result, we make a similar distinction in this work.…”

Section: Beam Energymentioning

confidence: 99%

“…However, given a luminosity determination from the SYMBs, the forward tracking telescopes could make a determination of hard TPE. This determination was reported in the OLYMPUS results [2]. The second system was the OLYMPUS slow control system, which recorded the beam current in the storage ring, the flow rate of hydrogen to the target, and the target temperature, which could be combined into a luminosity determination.…”

Section: The Olympus Experimentsmentioning

confidence: 99%

“…The OLYMPUS experiment [1] measured the ratio of positron-proton to electron-proton elastic scattering crosssections for a 2.01 GeV beam energy over a range of scattering angles [2]. The analysis depended on the accurate (better than 1%) determination of the relative integrated luminosity between positron-beam running mode and electron-beam running mode.…”

Section: Introductionmentioning

confidence: 99%

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A novel technique for determining luminosity in electron-scattering/positron-scattering experiments from multi-interaction events

Schmidt

O'Connor

Bernauer

et al. 2018

Nuclear Instruments and Methods in Physics Research Section A:

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The OLYMPUS experiment measured the cross-section ratio of positron-proton elastic scattering relative to electron-proton elastic scattering to look for evidence of hard two-photon exchange. To make this measurement, the experiment alternated between electron beam and positron beam running modes, with the relative integrated luminosities of the two running modes providing the crucial normalization. For this reason, OLYMPUS had several redundant luminosity monitoring systems, including a pair of electromagnetic calorimeters positioned downstream from the target to detect symmetric Møller and Bhabha scattering from atomic electrons in the hydrogen gas target. Though this system was designed to monitor the rate of events with single Møller/Bhabha interactions, we found that a more accurate determination of relative luminosity could be made by additionally considering the rate of events with both a Møller/Bhabha interaction and a concurrent elastic ep interaction. This method was improved by small corrections for the variance of the current within bunches in the storage ring and for the probability of three interactions occurring within a bunch. After accounting for systematic effects, we estimate that the method is accurate in determining the relative luminosity to within 0.36%. This precise technique can be employed in future electron-proton and positron-proton scattering experiments to monitor relative luminosity between different running modes.

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Two-Photon Exchange Correction in Elastic Lepton–Proton Scattering

Tomalak

2018

Few-Body Syst

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We present the dispersion relation approach based on unitarity and analyticity to evaluate the two-photon exchange contribution to elastic electron-proton scattering. The leading elastic and first inelastic πN intermediate state contributions are accounted for in the region of small momentum transfer Q 2 < 1 GeV 2 based on the available data input. The novel methods of analytical continuation allow us to exploit the MAMI form factor data and the MAID parameterization for the pion electroproduction amplitudes as input in the calculation. The results are compared to the recent CLAS, VEPP-3 and OLYMPUS data as well as to the full two-photon exchange correction in the near-forward approximation, which is based on the Christy and Bosted unpolarized structure functions fit. Additionally, predictions are given for a forthcoming muon-proton scattering experiment.

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Hard Two-Photon Contribution to Elastic Lepton-Proton Scattering Determined by the OLYMPUS Experiment

Cited by 88 publications

References 56 publications

Proton Charge Radius from Electron Scattering

Proton Charge Radius from Electron Scattering

A novel technique for determining luminosity in electron-scattering/positron-scattering experiments from multi-interaction events

Two-Photon Exchange Correction in Elastic Lepton–Proton Scattering

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