Erratum: Empirical parametrization of the two-photon-exchange effect contributions to the electron-proton elastic scattering cross section [Phys. Rev. C<b>83</b>, 054307 (2011)]

Qattan, I. A.; Alsaad, Ahmad

doi:10.1103/physrevc.84.029905

Cited by 19 publications

(31 citation statements)

References 7 publications

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“…Based on the observations above, it is possible to try and extract the TPE contributions based on the observed discrepancy between the LT and PT results. Assuming that the TPE contributions are linear in ε and that the PT results do not depend on ε, and knowing that the TPE contribution must vanish in the forward limit (ε → 1) [28,36], it is possible to extract the TPE contribution to the unpolarized cross section in a combined analysis of LT and PT data [7,16,[27][28][29]. Where polarization data exist as a function of ε, it is possible to attempt to extract the TPE amplitudes with fewer assumptions [30,37], though with relatively large uncertainties.…”

Section: Two-photon Exchange Contributionsmentioning

confidence: 99%

“…where R = µ p G p E /G p M is the recoil polarization ratio. We recently extracted the proton form factors and the TPE correction a(Q 2 ) for large Q 2 values [7,11] using the world data on σ R from Refs. [33,34,[39][40][41][42][43][44].…”

Section: Extraction Of the Form Factors And Tpementioning

confidence: 99%

“…In this paper, we extract the proton form factors from a combined analysis of LT and PT measurements, accounting for TPE contributions following the approach of Ref. [7], but with an emphasis on recent low-Q 2 data.…”

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confidence: 99%

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Flavor decomposition of the nucleon electromagnetic form factors

Qattan

Arrington

2012

Phys. Rev. C

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Background: The spatial distribution of charge and magnetization in the proton and neutron are encoded in the nucleon electromagnetic form factors. The form factors are all approximated by a simple dipole function, normalized to the charge or magnetic moment of the nucleon. The differences between the proton and neutron form factors and the deviation of G n E from zero are sensitive to the difference between up-and down-quark contributions to the form factors.Purpose: Recent measurements of G n E up to 3.4 (GeV/c) 2 allow for a much more detailed examination of the form factors. The flavor-separated form factors provide information on the quark flavor dependence of the nucleon structure and test theoretical models of the form factors.Methods: We combine recent measurements of the neutron form factors with updated extractions of the proton form factors, accounting for two-photon exchange corrections and including an estimate of the uncertainties for all of the form factors to obtain a complete set of measurements up to Q 2 ≈ 4 (GeV/c) 2 . We use this to extract the up-and down-quark contributions which we compare to recent fits and calculations.Results: We find a large differences between the up-and down-quark contributions to GE and GM , implying significant flavor dependence in the charge and magnetization distributions. The rapid falloff of the ratio G p E /G p M does not appear in the individual quark form factors, but arises from a cancellation between the up-and down-quark contributions. We see indications that the down-quark contributions to the Dirac and Pauli form factors deviate from the suggested 1/Q 4 scaling behavior suggested by a previous analysis. While recent models provide a generally good qualitative description of the data, the down-quark contribution to GE/GM and F2/F1 are not reproduced by any of the models. Finally, we note that while the inclusion of recent G n M data from CLAS modifies the high-Q 2 slightly, the tension between these data and previous measurements at lower Q 2 has a more significant impact, suggesting the need for additional data in this region.

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Section: Two-photon Exchange Contributionsmentioning

confidence: 99%

Section: Extraction Of the Form Factors And Tpementioning

confidence: 99%

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Flavor decomposition of the nucleon electromagnetic form factors

Qattan

Arrington

2012

Phys. Rev. C

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“…The role of TPE effects was studied extensively both theoretically [19][20][21][22][23][24] and phenomenologically [16,[25][26][27][28][29][30][31][32]. Most calculations suggested that the TPE corrections are relatively small, but have a significant angular dependence which mimics the effect of a larger value of G p E .…”

Section: Two-photon Exchange Contributionsmentioning

confidence: 99%

Flavor decomposition of the nucleon electromagnetic form factors at lowQ2

2015

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Background The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors.These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up-and down-quark contributions.Purpose In this work, we extract the proton and neutron form factors from world's data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we separate the up-and down-quark contributions to the proton form factors.Method We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parameterization of the neutron form factor data and uncertainties to separate the up-and down-quark contributions to the proton's charge and magnetic form factors.Results The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavor-separated form factors are extracted and compared to models of the nucleon structure.Conclusions With the inclusion of the precise new data, the extracted TPE contributions show a clear change of sign at low Q 2 , necessary to explain the high-Q 2 form factor discrepancy while being consistent with the known Q 2 → 0 limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavorseparated contributions. We also observe that the RMS radius of both the up-and down-quark distributions are smaller than the RMS charge radius of the proton.

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“…If the α parameter is small then the penalty term (13) does not significantly affect the results of the training process. In the language of the Bayesian statistics, a small α value corresponds to the large width of the prior probability distribution (12).…”

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confidence: 99%

Two-photon exchange effect studied with neural networks

Graczyk

2011

Phys. Rev. C

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An approach to the extraction of the two-photon exchange (TPE) correction from elastic ep scattering data is presented. The cross section, polarization transfer (PT), and charge asymmetry data are considered. It is assumed that the TPE correction to the PT data is negligible. The form factors and TPE correcting term are given by one multidimensional function approximated by the feed forward neural network (NN). To find a model-independent approximation the Bayesian framework for the NNs is adapted. A large number of different parametrizations is considered. The most optimal model is indicated by the Bayesian algorithm. The obtained fit of the TPE correction behaves linearly in ǫ but it has a nontrivial Q 2 dependence. A strong dependence of the TPE fit on the choice of parametrization is observed.

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Erratum: Empirical parametrization of the two-photon-exchange effect contributions to the electron-proton elastic scattering cross section [Phys. Rev. C83, 054307 (2011)]

Cited by 19 publications

References 7 publications

Flavor decomposition of the nucleon electromagnetic form factors

Flavor decomposition of the nucleon electromagnetic form factors

Flavor decomposition of the nucleon electromagnetic form factors at lowQ2

Two-photon exchange effect studied with neural networks

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