High precision measurements of the proton elastic electromagnetic form factors and their ratio at <math xmlns="http://www.w3.org/1998/Math/MathML"><msup><mi>Q</mi><mn>2</mn></msup></math> = 0.50, 2.64, 3.20, and <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mn>4.10</mn><mspace width="0.16em"></mspace><msup><mrow><mi>GeV</mi></mrow><mn>2</mn></msup></mrow></math>

I. A. Qattan; J. Arrington; K. Aniol; O. K. Baker; R. Beams; E. J. Brash; A. Camsonne; J.-P. Chen; M. E. Christy; D. Dutta; R. Ent; D. Gaskell; O. Gayou; R. Gilman; J.-O. Hansen; D. W. Higinbotham; R. J. Holt; G. M. Huber; H. Ibrahim; L. Jisonna; M. K. Jones; C. E. Keppel; E. Kinney; G. J. Kumbartzki; A. Lung; K. McCormick; D. Meekins; R. Michaels; P. Monaghan; L. Pentchev; R. Ransome; J. Reinhold; B. Reitz; A. Sarty; E. C. Schulte; K. Slifer; R. E. Segel; V. Sulkosky; M. Yurov; X. Zheng

doi:10.1103/4vmq-s4c7

High precision measurements of the proton elastic electromagnetic form factors and their ratio at $Q^{2}$ = 0.50, 2.64, 3.20, and $4.10 {GeV}^{2}$

I. A. Qattan^1,2, J. Arrington ^3,4, K. Aniol⁵, O. K. Baker⁶, R. Beams ⁴, E. J. Brash⁷, A. Camsonne ⁸, J.-P. Chen ⁹, M. E. Christy ⁶ et al.

D. Dutta ¹⁰, R. Ent ⁹, D. Gaskell ¹¹, O. Gayou¹², R. Gilman ^13,9, J.-O. Hansen ⁹, D. W. Higinbotham⁹, R. J. Holt ^4,*, G. M. Huber ⁷, H. Ibrahim^14,15, L. Jisonna ², M. K. Jones ⁹, C. E. Keppel⁶, E. Kinney ¹¹, G. J. Kumbartzki ¹³, A. Lung⁹, K. McCormick ¹³, D. Meekins ⁹, R. Michaels⁹, P. Monaghan¹⁰, L. Pentchev¹², R. Ransome¹³, J. Reinhold ¹⁶, B. Reitz ⁹, A. Sarty ¹⁷, E. C. Schulte⁴, K. Slifer ¹⁸, R. E. Segel ², V. Sulkosky¹², M. Yurov ^19,20, and X. Zheng ^4,†

¹Khalifa University of Science and Technology, Abu Dhabi, P. O. Box 127788, United Arab Emirates
²Northwestern University, Evanston, Illinois 60208, USA
³Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
⁴Argonne National Laboratory, Argonne, Illinois 60439, USA
⁵California State University, Los Angeles, Los Angeles, California 90032, USA
⁶Hampton University, Hampton, Virginia 23668, USA
⁷University of Regina, Regina, Saskatchewan, Canada, S4S 0A2
⁸Université Blaise Pascal Clermont-Ferrand et CNRS/IN2P3 LPC 63, 177 Aubière Cedex, France
⁹Jefferson Laboratory, Newport News, Virginia 23606, USA
¹⁰Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
¹¹University of Colorado, Boulder, Colorado 80309, USA
¹²College of William and Mary, Williamsburg, Virginia 23187, USA
¹³Rutgers, The State University of New Jersey, Piscataway, New Jersey 08855, USA
¹⁴Old Dominion University, Norfolk, Virginia 23529, USA
¹⁵Cairo University, Giza, 121613, Egypt
¹⁶Florida International University, Miami, Florida 33199, USA
¹⁷Saint Mary's University, Halifax, Nova Scotia, Canada B3H 3C3
¹⁸Temple University, Philadelphia, Pennsylvania 19122, USA
¹⁹Mississippi State University, Starkville, Mississippi 39762, USA
²⁰Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA

^*Present address: California Institute of Technology, Pasadena, California 91125, USA.
^†Present address: University of Virginia, Charlottesville, Virginia 22904, USA.

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Phys. Rev. C 112, 035205 – Published 17 September, 2025

DOI: https://doi.org/10.1103/4vmq-s4c7

Abstract

Background: The advent of high-intensity, high-polarization electron beams led to significantly improved measurements of the ratio of the proton’s charge to electric form factors, $G_{E p} / G_{M p}$ . However, high- $Q^{2}$ measurements of this ratio yielded significant disagreement with extractions based on unpolarized scattering measurements, raising questions about the reliability of the measurements and consistency of the techniques.

Purpose: Jefferson Lab experiment E01-001 was designed to provide a high precision extraction of $G_{E p} / G_{M p}$ from unpolarized cross-section measurements using a modified version of the Rosenbluth separation technique to allow for a more precise comparison with polarization data.

Method: Rosenbluth separations involve precise measurements of the angular dependence of the elastic $e − p$ cross section at fixed momentum transfer, $Q^{2}$ . Conventional Rosenbluth separations detect the scattered electron, requiring the comparisons of measurements with very different detected electron energy and rate for electrons at different angles. Our ‘‘super-Rosenbluth’’ measurement detected the struck proton, rather than the scattered electron to extract the elastic $e − p$ cross section. This yielded a fixed momentum for the detected particle and dramatically reduced variation of the cross section with angle, significantly reducing rate- and momentum-dependent corrections and uncertainties.

Results: We measure the cross section vs angle with high relative precision, allowing for extremely high precision extractions of $G_{E p} / G_{M p}$ at $Q^{2}$ = 2.64, 3.20, and $4.10 {GeV}^{2}$ . Our results are consistent with traditional Rosenbluth extractions, but with much smaller corrections and systematic uncertainties, comparable to the uncertainties from polarization measurements.

Conclusions: Our data confirm the discrepancy between Rosenbluth and polarization extractions of the proton form factor ratio using an improved Rosenbluth extraction that yields smaller and less-correlated uncertainties than those typical of previous Rosenbluth extractions. We compare our results to calculations of two-photon exchange effects and find that the observed discrepancy can be relatively well explained by such effects.

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17 February, 2026

Correction: A second affiliation for author H. Ibrahim was missing at publication and has been added.

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High precision measurements of the proton elastic electromagnetic form factors and their ratio at $Q^{2}$ = 0.50, 2.64, 3.20, and $4.10 {GeV}^{2}$

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New extraction of the nucleon charge radius utilizing electron-proton elastic scattering experimental data

New extraction of the proton's conventional charge and magnetic radii utilizing electron-proton elastic scattering experimental data

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High precision measurements of the proton elastic electromagnetic form factors and their ratio at Q2 = 0.50, 2.64, 3.20, and 4.10GeV2

Abstract

Physics Subject Headings (PhySH)

Corrections

See Also

New extraction of the nucleon charge radius utilizing electron-proton elastic scattering experimental data

New extraction of the proton's conventional charge and magnetic radii utilizing electron-proton elastic scattering experimental data

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High precision measurements of the proton elastic electromagnetic form factors and their ratio at $Q^{2}$ = 0.50, 2.64, 3.20, and $4.10 {GeV}^{2}$