2003
DOI: 10.1103/physrevlett.91.142303
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How to Reconcile the Rosenbluth and the Polarization Transfer Methods in the Measurement of the Proton Form Factors

Abstract: The apparent discrepancy between the Rosenbluth and the polarization transfer methods for the ratio of the electric to magnetic proton form factors can be explained by a two-photon exchange correction which does not destroy the linearity of the Rosenbluth plot. Though intrinsically small, of the order of a few percent of the cross section, this correction is accidentally amplified in the case of the Rosenbluth method.

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Cited by 382 publications
(535 citation statements)
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References 12 publications
(26 reference statements)
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“…The question of the zero crossing for G p E is not yet settled because the experimental errors are still too large, but the situation is expected to change in the near future with the Jefferson Lab 12 GeV program where measurements in Halls A, B and C will extend the data range for G p E , G n E , and G n M up to the 10 -14 GeV 2 region [572]. It is established by now that two-photon exchange corrections can explain the discrepancy in principle [573,574], although the effect is still not completely understood because it cannot be calculated model-independently and the existing model calculations rely on different underlying mechanisms. More surprises have also been found at low Q 2 , where the present data for G p E are incompatible with the muonic hydrogen result for the proton's charge radius.…”
Section: Nucleon Electromagnetic Form Factorsmentioning
confidence: 99%
“…The question of the zero crossing for G p E is not yet settled because the experimental errors are still too large, but the situation is expected to change in the near future with the Jefferson Lab 12 GeV program where measurements in Halls A, B and C will extend the data range for G p E , G n E , and G n M up to the 10 -14 GeV 2 region [572]. It is established by now that two-photon exchange corrections can explain the discrepancy in principle [573,574], although the effect is still not completely understood because it cannot be calculated model-independently and the existing model calculations rely on different underlying mechanisms. More surprises have also been found at low Q 2 , where the present data for G p E are incompatible with the muonic hydrogen result for the proton's charge radius.…”
Section: Nucleon Electromagnetic Form Factorsmentioning
confidence: 99%
“…(3,4) and (5) is described by the form factors F 1,2 , F γN ∆ and F γ∆∆ . The form factors are necessary to ensure ultraviolet convergence of the loop integrals calculated in Section V. The results presented below were obtained using the standard dipole form for all these form factors:…”
Section: Hadronic Vertex Functions and Propagatorsmentioning
confidence: 99%
“…This can be verified by using the hadron-photon vertices Eqs. (3)(4)(5), the free nucleon propagator S(p) and the Dirac equation for the incoming nucleon and outgoing ∆. To obtain a gauge invariant amplitude, an additional γγN∆ contact term M ct αµν (q ′ , q; p ′ , p) (depicted by the triangle in Fig.…”
Section: Gauge Invariance and The γγN ∆ Contact Termmentioning
confidence: 99%
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“…Thus, it came as a surprise when the Jefferson Lab Hall A recoil polarization measurements of electron-proton elastic scattering at momentum transfers of about 2 (GeV/c) 2 [18] showed a substantial deviation from the data obtained over several decades with the Rosenbluth technique [19], which is based on precise cross-section measurements. This discrepancy has been interpreted as the effect of multiple photon exchange in the elastic electron-proton crosssection [20]. The cross section for elastic electron-proton scattering in the one-photon exchange approximation can be written in terms of the pointlike Mott cross-section, the Sachs form factors G p E and G p M and the electron scattering angle θ as…”
Section: Introductionmentioning
confidence: 99%