Journal
PHYSICAL REVIEW C
Volume 85, Issue 4, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevC.85.045203
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Funding
- Jefferson Lab Accelerator Division
- US Department of Energy [DEAC05-84ER40150]
- US National Science Foundation
- Italian Istituto Nazionale di Fisica Nucleare (INFN)
- French Commissariat a l'Energie Atomique (CEA)
- Centre National de la Recherche Scientifique [CNRS-IN2P3]
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- EEC [INTAS 99-00125]
- Swedish Natural Science Research Council
- Los Alamos National Laboratory
- [CRDF UP2-2271]
- Direct For Mathematical & Physical Scien
- Division Of Physics [1066374, 969380] Funding Source: National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Physics [0901951, 753777] Funding Source: National Science Foundation
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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.
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