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Physical Review C 85 (2012) 045203
Final analysis of proton form factor ratio data at Q2=4.0, 4.8, and 5.6 GeV2
A. J. R. Puckett1, C. Cavata1, S. Escoffier1, D. Lhuillier1, F. Marie1, D. Neyret1, E. Tomasi-Gustafsson1, 2, O. Gayou3, H. Fonvieille3, L. Bimbot2
HALL A Collaboration(s)

Precise measurements of the proton electromagnetic form factor ratio R=μpGEp/GMp 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 Q2 for Q2≳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 Q2 values in the range 3.5 GeV2≤Q2≤5.6 GeV2. A possible discrepancy between the originally published GEp-II results and more recent measurements at higher Q2 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-Q2 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.
1 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
2 :  IPNO - Institut de Physique Nucléaire d'Orsay
3 :  LPC - Laboratoire de Physique Corpusculaire [Clermont-Ferrand]
Physique/Physique Nucléaire Expérimentale