Final analysis of proton form factor ratio data at Q(2)=4.0, 4.8, and 5.6 GeV2

Research output: Contribution to journalArticle


Precise measurements of the proton electromagnetic form factor ratio R = mu(p)G(E)(p)/G(M)(p) using the polarization transfer method at Jefferson Lab have revolutionized the understanding of nucleon structure by revealing the strong decrease of R with momentum transfer Q(2) for Q(2) greater than or similar to 1 GeV2, in strong disagreement with previous extractions of R from cross-section measurements. In particular, the polarization transfer results have exposed the limits of applicability of the one-photon-exchange approximation and highlighted the role of quark orbital angular momentum in the nucleon structure. The GEp-II experiment in Jefferson Lab's Hall A measured R at four Q(2) values in the range 3.5 GeV2 <= Q(2) <= 5.6 GeV2. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher Q(2) motivated a new analysis of the GEp-II data. This article presents the final results of the GEp-II experiment, including details of the new analysis, an expanded description of the apparatus, and an overview of theoretical progress since the original publication. The key result of the final analysis is a systematic increase in the results for R, improving the consistency of the polarization transfer data in the high-Q(2) region. This increase is the result of an improved selection of elastic events which largely removes the systematic effect of the inelastic contamination, underestimated by the original analysis.


  • A. J. R. Puckett
  • E. J. Brash
  • O. Gayou
  • M. K. Jones
  • L. Pentchev
  • C. F. Perdrisat
  • V. Punjabi
  • K. A. Aniol
  • T. Averett
  • F. Benmokhtar
  • W. Bertozzi
  • L. Bimbot
  • J. R. Calarco
  • C. Cavata
  • Z. Chai
  • C. -C. Chang
  • T. Chang
  • J. P. Chen
  • E. Chudakov
  • R. De Leo
  • S. Dieterich
  • R. Endres
  • M. B. Epstein
  • S. Escoffier
  • H. Fonvieille
  • S. Frullani
  • J. Gao
  • F. Garibaldi
  • S. Gilad
  • R. Gilman
  • A. Glamazdin
  • C. Glashausser
  • J. Gomez
  • J. -O. Hansen
  • D. Higinbotham
  • G. M. Huber
  • M. Iodice
  • C. W. de Jager
  • X. Jiang
  • M. Khandaker
  • S. Kozlov
  • K. M. Kramer
  • G. Kumbartzki
  • J. J. LeRose
  • D. Lhuillier
  • R. A. Lindgren
  • N. Liyanage
  • G. J. Lolos
  • D. J. Margaziotis
  • F. Marie
  • P. Markowitz
  • K. McCormick
  • R. Michaels
  • B. D. Milbrath
  • S. K. Nanda
  • D. Neyret
  • N. M. Piskunov
  • R. D. Ransome
  • B. A. Raue
  • R. Roche
  • M. Rvachev
  • C. Salgado
  • S. Sirca
  • I. Sitnik
  • S. Strauch
  • L. Todor
  • E. Tomasi-Gustafsson
  • G. M. Urciuoli
  • H. Voskanyan
  • K. Wijesooriya
  • B. B. Wojtsekhowski
  • X. Zheng
  • L. Zhu
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Subatomic Physics
Original languageEnglish
JournalPhysical Review C (Nuclear Physics)
Issue number4
Publication statusPublished - 2012
Publication categoryResearch

Total downloads

No data available