Towards a resolution of the proton form factor problem: new electron and positron scattering data
Creators: name: Adikaram, D.
name: Rimal, D.
name: Weinstein, L. B.
name: Raue, B.
name: Khetarpal, P.
name: Bennett, R. P.
name: Arrington, J.
name: Brooks, W. K.
name: Adhikari, K. P.
name: Afanasev, A. V.
name: Amaryan, M. J.
name: Anderson, M. D.
name: Ball, J.
name: Battaglieri, M.
name: Bedlinskiy, I.
name: Biselli, A. S.
name: Bono, J.
name: Boiarinov, S.
name: Briscoe, W. J.
name: Burkert, V. D.
name: Carman, D. S.
name: Celentano, A.
name: Chandavar, S.
name: Charles, G.
name: Colaneri, L.
name: Cole, P. L.
name: Contalbrigo, M.
name: D'Angelo, A.
name: Dashyan, N.
name: De Vita, R.
name: De Sanctis, E.
name: Deur, A.
name: Djalali, C.
name: Dodge, G. E.
name: Dupre, R.
name: Egiyan, H.
name: Alaoui, A. El
name: Fassi, L. El
name: Eugenio, P.
name: Fedotov, G.
name: Fegan, S.
name: Filippi, A.
name: Fleming, J. A.
name: Fradi, A.
name: Gilfoyle, G. P.
name: Giovanetti, K. L.
name: Girod, F. X.
name: Goetz, J. T.
name: Gohn, W.
name: Golovatch, E.
name: Gothe, R. W.
name: Griffioen, K. A.
name: Guidal, M.
name: Guo, L.
name: Hafidi, K.
name: Hakobyan, H.
name: Harrison, N.
name: Hattawy, M.
name: Hicks, K.
name: Holtrop, M.
name: Hughes, S. M.
name: Hyde, C. E.
name: Ilieva, Y.
name: Ireland, D. G.
name: Ishkhanov, B. S.
name: Jenkins, D.
name: Jiang, H.
name: Joo, K.
name: Joosten, S.
name: Khandaker, M.
name: Kim, W.
name: Klein, A.
name: Klein, F. J.
name: Koirala, S.
name: Kubarovsky, V.
name: Kuhn, S. E.
name: Lu, H. Y.
name: MacGregor, I . J . D.
name: Markov, N.
name: Mayer, M.
name: McKinnon, B.
name: Mestayer, M. D.
name: Meyer, C. A.
name: Mirazita, M.
name: Mokeev, V.
name: Montgomery, R. A.
name: Moody, C. I.
name: Moutarde, H.
name: Movsisyan, A
name: Camacho, C. Munoz
name: Nadel-Turonski, P.
name: Niccolai, S.
name: Niculescu, G.
name: Osipenko, M.
name: Ostrovidov, A. I.
name: Park, K.
name: Pasyuk, E.
name: Pisano, S.
name: Pogorelko, O.
name: Procureur, S.
name: Prok, Y.
name: Protopopescu, D.
name: Puckett, A. J. R.
name: Ripani, M.
name: Rizzo, A.
name: Rosner, G.
name: Rossi, P.
name: Sabatié, F.
name: Schott, D.
name: Schumacher, R. A.
name: Sharabian, Y. G.
name: Simonyan, A.
name: Skorodumina, I.
name: Smith, E. S.
name: Smith, G. D.
name: Sober, D. I.
name: Sparveris, N.
name: Stepanyan, S.
name: Strauch, S.
name: Sytnik, V.
name: Taiuti, M.
name: Tian, Ye
name: Trivedi, A.
name: Ungaro, M.
name: Voskanyan, H.
name: Voutier, E.
name: Walford, N. K.
name: Watts, D. P.
name: Wei, X.
name: Wood, M. H.
name: Zachariou, N.
name: Zana, L.
name: Zhang, J.
name: Zhao, Z. W.
name: Zonta, I.
name: Collaboration, The CLAS
Publisher: name: arXiv
Year: 2014
Subjects: subject: Nuclear Experiment (nucl-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: There is a significant discrepancy between the values of the proton electric form factor, $G_E^p$, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of $G_E^p$ from the unpolarized electron-proton cross sections. We determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections using a simultaneous, tertiary electron-positron beam incident on a liquid hydrogen target and detecting the scattered particles in the Jefferson Lab CLAS detector. This novel technique allowed us to cover a wide range in virtual photon polarization ($\varepsilon$) and momentum transfer ($Q^2$) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing $\varepsilon$ at $Q^2 = 1.45 \text{ GeV}^2$. This measurement is consistent with the size of the form factor discrepancy at $Q^2\approx 1.75$ GeV$^2$ and with hadronic calculations including nucleon and $Δ$ intermediate states, which have been shown to resolve the discrepancy up to $2-3$ GeV$^2$.
description: 6 pages, 4 figures, submitted to PRL