Hard two-photon contribution to elastic lepton-proton scattering determined by the OLYMPUS experiment

Henderson, B. S. et al. (2017) Hard two-photon contribution to elastic lepton-proton scattering determined by the OLYMPUS experiment. Physical Review Letters, 118(9), 092501. (doi: 10.1103/PhysRevLett.118.092501)

Abstract

The OLYMPUS Collaboration reports on a precision measurement of the positron-proton to electron-proton elastic cross section ratio, R 2 γ , 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 gas electron multiplier and multiwire proportional chamber detectors at 12°, as well as symmetric Møller or Bhabha calorimeters at 1.29°. A total integrated luminosity of 4.5     fb − 1 was collected. In the extraction of R 2 γ , 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 R 2 γ , presented here for a wide range of virtual photon polarization 0.456 < ε < 0.978 , are smaller than some hadronic two-photon exchange calculations predict, but are in reasonable agreement with a subtracted dispersion model and a phenomenological fit to the form factor data.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Murray, Dr Morgan and Lumsden, Mr Peter and Kaiser, Professor Ralf and Lehmann, Dr Inti and Seitz, Dr Bjoern and Rosner, Professor Guenther
• Authors: Henderson, B. S., Ice, L. D., Khaneft, D., O’Connor, C., Russell, R., Schmidt, A., Bernauer, J. C., Kohl, M., Akopov, N., Alarcon, R., Ates, O., Avetisyan, A., Beck, R., Belostotski, S., Bessuille, J., Brinker, F., Calarco, J. R., Carassiti, V., Cisbani, E., Ciullo, G., Contalbrigo, M., De Leo, R., Diefenbach, J., Donnelly, T. W., Dow, K., Elbakian, G., Eversheim, P. D., Frullani, S., Funke, C., Gavrilov, G., Gläser, B., Görrissen, N., Hasell, D. K., 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, D., Lumsden, S., Ma, Y., Maas, F., Marukyan, H., Miklukho, O., Milner, R. G., Movsisyan, A., Murray, M., Naryshkin, Y., Perez Benito, R., Perrino, R., Redwine, R. P., Rodríguez Piñeiro, D., Rosner, G., Schneekloth, U., Seitz, B., Statera, M., Thiel, A., Vardanyan, H., Veretennikov, D., Vidal, C., Winnebeck, A., and Yeganov, V.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Physical Review Letters
• Publisher: American Physical Society
• ISSN: 0031-9007
• ISSN (Online): 1079-7114
• Copyright Holders: Copyright © 2017 American Physical Society
• First Published: First published in Physical Review Letters 118(9): 092501
• Publisher Policy: Reproduced in accordance with the publisher copyright policy