Two-photon exchange contribution to elastic electron-proton scattering: Measurements at the VEPP-3 storage ring

I. A. Rachek, J. Arrington, V. F. Dmitriev, Vyacheslav Valerievich Gauzshtein, A. V. Gramolin, R. J. Holt, V. V. Kaminskiy, B. A. Lazarenko, S. I. Mishnev, N. Yu Muchnoi, V. V. Neufeld, D. M. Nikolenko, R. Sh Sadykov, Yu V. Shestakov, V. N. Stibunov, D. K. Toporkov, H. De Vries, S. A. Zevakov, V. N. Zhilich

Research output: Contribution to journalConference articlepeer-review


A striking discrepancy between the results for the ratio of electric and magnetic form factors of the proton obtained by two approaches: the Rosenbluth extraction from the unpolarized cross section and the double-polarization measurements has led to a serious re-examination of the role played by two-photon exchange diagrams. The evaluation of such diagrams could not be done in model-independent way, which means an experimental verification is required. One of the direct ways to do this is to measure the ratio of positron-proton and electron-proton elastic scattering cross-sections for identical kinematics. Such a measurement has been performed at the VEPP-3 storage ring at Novosibirsk. There were two runs at beam energies of 1.6 and 1.0 GeV at several ranges of scattering angle. The measurements covered the transferred momentum Q2 up to 1.5 GeV2 and the virtual photon polarization parameter down to 0.2 . The VEPP-3 experimental approach is described and the results of the measurements are presented.

Original languageEnglish
Article number014017
JournalPhysica Scripta
Issue numberT166
Publication statusPublished - 1 Nov 2015
Event9th International Conference on Nuclear Physics at Storage Rings, STORI 2014 - Sankt Goar, Germany
Duration: 29 Sep 20143 Oct 2014


  • elastic scattering
  • proton form factors
  • two-photon exchange

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Mathematical Physics
  • Condensed Matter Physics

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