Two-Photon Exchange: Myth and History

Tomasi–Gustafsson, E.; Pacetti, S.

doi:10.1007/s00601-018-1416-5

Cited by 9 publications

(2 citation statements)

References 51 publications

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“…Below in the reliability analysis of the experimental measurements [8], it will be established on the basis of the results [43] that ∆ 0 is determined by the normalization uncertainty. Note that the limits on the kinematics of the experiment conducted using RT was not considered in the literature, including [42,43,49,50]. Nevertheless, it seems to be an important issue that deserves attention.…”

Section: A Results Of Numerical Calculations and Their Discussionmentioning

confidence: 99%

Reliability Analysis of the Results of the Known Experiments on Measuring of the Sachs Form Factor Ratio Using the Rosenbluth Technique. Polarization of the Final Proton in the $e \vec p \to e \vec p$ Elastic Process

Galynskii

2021

Preprint

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A criterion for assessing the reliability of measurements of the Sachs form factor ratio using the Rosenbluth technique is proposed and applied to an analysis of three known experiments (Andi-vahis1994, Walker1994, Qattan2005) and a recent experiment on the CEBAF accelerator upgraded to 12 GeV at JLab (arXiv:2103.01842 [nucl-ex]). Based on the results of the JLab polarization experiments on measuring the ratio µpGE/GM in the ep → e p process, in the kinematics of the SANE experiment (2020) on the measurement of double spin asymmetry in the e p → ep process numerical calculations are performed for the Q 2 dependence of polarization transferred to the proton in the e p → e p process when the initial proton at rest is partially polarized along the direction of motion of the detected recoil proton.

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Section: A Results Of Numerical Calculations and Their Discussionmentioning

confidence: 99%

Reliability Analysis of the Results of the Known Experiments on Measuring of the Sachs Form Factor Ratio Using the Rosenbluth Technique. Polarization of the Final Proton in the $e \vec p \to e \vec p$ Elastic Process

Galynskii

2021

Preprint

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“…The restrictions on the kinematics of experiments where the RT is used have not yet been considered in publications, including [25][26][27]. This problem is nevertheless of importance and deserves special attention.…”

mentioning

confidence: 99%

On the Transfer of Polarization from the Initial to the Final Proton in the Elastic Process $ e \vec {p} \to e \vec {p}$

Galynskii

2021

Preprint

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The Q 2 dependence of the ratio of the cross sections with and without spin flip, as well as the polarization asymmetry in the process e p → e p has been numerically analyzed using the results of JLab's polarization experiments on the measurements of the ratio of the Sachs form factors in the ep → e p process. The calculations have been made for the case where the initial (at rest) and final protons are fully polarized and have a common spin quantization axis, which coincides with the direction of motion of the final proton. The longitudinal polarization transfer to the proton has been calculated in the case of the partially polarized initial proton for a kinematics used in the experiment reported in [A. Liyanage et al. (SANE Collaboration), Phys. Rev. C 101, 035206 (2020)], where the double spin asymmetry was measured in the e p → ep process. A noticeable sensitivity of the polarization transfer to the proton to the form of the Q 2 dependence of the ratio µpGE/GM has been found. This sensitivity may be used to conduct a new independent experiment to measure this dependence in the e p → e p process. A criterion to assess the reliability of measurements of the ratio of Sachs form factors using the Rosenbluth technique has been proposed and used to analyze the results of two experiments.

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Two-Photon Exchange: Future Experimental Prospects

Bernauer

2018

Few-Body Syst

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The proton elastic form factor ratio is accessible in unpolarized Rosenbluthtype experiments as well as experiments which make use of polarization degrees of freedom. The extracted values show a distinct discrepancy, growing with Q 2 . Three recent experiments tested the proposed explanation, two-photon exchange, by measuring the positron-proton to electron-proton cross section ratio. In the results, a small two-photon exchange effect is visible, significantly different from theoretical calculation. Theory at larger momentum transfer remains untested. This paper discusses the possibilities for future measurements at larger momentum transfer.Keywords proton · form factor · two-photon exchange PACS 13.40.Gp · 14.20.Dh · 25.30.Bf IntroductionProton elastic form factors have been studied intensively with electron-proton scattering using unpolarized beams and target. The experiments produced data over an extensive range of (negative) four-momentum transfers, Q 2 . Via the so-called Rosenbluth separation technique, the two elastic form factors were separated. More recently, experiments exploiting the polarization of beam or target measured the form factor ratio directly. While the former see rough agreement with scaling, i.e., a more or less constant ratio even for large Q 2 , the latter show a roughly linear fall-off of the ratio. Figure 1 shows a selection of the available data and recent fits.The form factors encode the distribution of charge and magnetization in the proton and this "form factor ratio puzzle" is a limiting factor in their precise determination. It is therefore of importance to resolve this puzzle.

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Two-Photon Exchange: Myth and History

Cited by 9 publications

References 51 publications

Reliability Analysis of the Results of the Known Experiments on Measuring of the Sachs Form Factor Ratio Using the Rosenbluth Technique. Polarization of the Final Proton in the $e \vec p \to e \vec p$ Elastic Process

Reliability Analysis of the Results of the Known Experiments on Measuring of the Sachs Form Factor Ratio Using the Rosenbluth Technique. Polarization of the Final Proton in the $e \vec p \to e \vec p$ Elastic Process

On the Transfer of Polarization from the Initial to the Final Proton in the Elastic Process $ e \vec {p} \to e \vec {p}$

Two-Photon Exchange: Future Experimental Prospects

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