Towards a resolution of the proton form factor problem: new electron and positron scattering data
Adikaram, D. · Rimal, D. · Weinstein, L. B. · Raue, B. · Khetarpal, P. · Bennett, R. P. · Arrington, J. · Brooks, W. K. · Adhikari, K. P. · Afanasev, A. V. · Amaryan, M. J. · Anderson, M. D. · Ball, J. · Battaglieri, M. · Bedlinskiy, I. · Biselli, A. S. · Bono, J. · Boiarinov, S. · Briscoe, W. J. · Burkert, V. D. · Carman, D. S. · Celentano, A. · Chandavar, S. · Charles, G. · Colaneri, L. · Cole, P. L. · Contalbrigo, M. · D'Angelo, A. · Dashyan, N. · De Vita, R. · De Sanctis, E. · Deur, A. · Djalali, C. · Dodge, G. E. · Dupre, R. · Egiyan, H. · Alaoui, A. El · Fassi, L. El · Eugenio, P. · Fedotov, G. · Fegan, S. · Filippi, A. · Fleming, J. A. · Fradi, A. · Gilfoyle, G. P. · Giovanetti, K. L. · Girod, F. X. · Goetz, J. T. · Gohn, W. · Golovatch, E. · Gothe, R. W. · Griffioen, K. A. · Guidal, M. · Guo, L. · Hafidi, K. · Hakobyan, H. · Harrison, N. · Hattawy, M. · Hicks, K. · Holtrop, M. · Hughes, S. M. · Hyde, C. E. · Ilieva, Y. · Ireland, D. G. · Ishkhanov, B. S. · Jenkins, D. · Jiang, H. · Joo, K. · Joosten, S. · Khandaker, M. · Kim, W. · Klein, A. · Klein, F. J. · Koirala, S. · Kubarovsky, V. · Kuhn, S. E. · Lu, H. Y. · MacGregor, I . J . D. · Markov, N. · Mayer, M. · McKinnon, B. · Mestayer, M. D. · Meyer, C. A. · Mirazita, M. · Mokeev, V. · Montgomery, R. A. · Moody, C. I. · Moutarde, H. · Movsisyan, A · Camacho, C. Munoz · Nadel-Turonski, P. · Niccolai, S. · Niculescu, G. · Osipenko, M. · Ostrovidov, A. I. · Park, K. · Pasyuk, E. · Pisano, S. · Pogorelko, O. · Procureur, S. · Prok, Y. · Protopopescu, D. · Puckett, A. J. R. · Ripani, M. · Rizzo, A. · Rosner, G. · Rossi, P. · Sabatié, F. · Schott, D. · Schumacher, R. A. · Sharabian, Y. G. · Simonyan, A. · Skorodumina, I. · Smith, E. S. · Smith, G. D. · Sober, D. I. · Sparveris, N. · Stepanyan, S. · Strauch, S. · Sytnik, V. · Taiuti, M. · Tian, Ye · Trivedi, A. · Ungaro, M. · Voskanyan, H. · Voutier, E. · Walford, N. K. · Watts, D. P. · Wei, X. · Wood, M. H. · Zachariou, N. · Zana, L. · Zhang, J. · Zhao, Z. W. · Zonta, I. · Collaboration, The CLAS
الأصل · EN
There is a significant discrepancy between the values of the proton electric form factor, Gₑᵖ, extracted using unpolarized and polarized electron scattering. Calculations predict that small two-photon exchange (TPE) contributions can significantly affect the extraction of Gₑᵖ 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 (ε) and momentum transfer (Q²) simultaneously, as well as to cancel luminosity-related systematic errors. The cross section ratio increases with decreasing ε at Q² = 1.45 GeV². This measurement is consistent with the size of the form factor discrepancy at Q²≈ 1.75 GeV² and with hadronic calculations including nucleon and Δ intermediate states, which have been shown to resolve the discrepancy up to 2-3 GeV².
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