Two-photon-exchange amplitude with<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>π</mml:mi><mml:mi>N</mml:mi></mml:mrow></mml:math>intermediate states:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>P</mml:mi><mml:mn>33</mml:mn></mml:msub></mml:math>channel

Borisyuk, Dmitry; Kobushkin, A. P.

doi:10.1103/physrevc.89.025204

Cited by 41 publications

(50 citation statements)

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“…Moreover, their shown result from such a calculation with g C = 0 also deviates from the original paper [26] but the NFF dependence is not further studied or discussed at all. Further calculations for different kinematics and assumptions are not directly comparable [36][37][38][39].…”

Section: Two-photon Exchange: ∆ Intermediate Statesmentioning

confidence: 99%

Theoretical constraints and systematic effects in the determination of the proton form factors

et al. 2015

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We calculate the two-photon exchange corrections to electron-proton scattering with nucleon and ∆ intermediate states. The results show a dependence on the elastic nucleon and nucleon-∆-transition form factors used as input which leads to significant changes compared to previous calculations. We discuss the relevance of these corrections and apply them to the most recent and precise data set and world data from electron-proton scattering. Using this, we show how the form factor extraction from these data is influenced by the subsequent inclusion of physical constraints. The determination of the proton charge radius from scattering data is shown to be dominated by the enforcement of a realistic spectral function. Additionally, the third Zemach moment from the resulting form factors is calculated. The obtained radius and Zemach moment are shown to be consistent with Lamb shift measurements in muonic hydrogen.

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Section: Two-photon Exchange: ∆ Intermediate Statesmentioning

confidence: 99%

Theoretical constraints and systematic effects in the determination of the proton form factors

et al. 2015

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“…During last decade, TPE was studied rather thoroughly, and the corresponding amplitude was calculated by different authors in various approximations and kinematical conditions; we will not discuss it in detail here, but will just refer to the known results [4,7,8].…”

Section: Introductionmentioning

confidence: 99%

Radiative corrections to polarization observables in electron-proton scattering

Borisyuk

Kobushkin

2014

Phys. Rev. C

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We consider radiative corrections to polarization observables in elastic electron-proton scattering, in particular, for the polarization transfer measurements of the proton form factor ratio µGE/GM . The corrections are of two types: two-photon exchange (TPE) and bremsstrahlung (BS); in the present work we pay special attention to the latter. Assuming small missing energy or missing mass cut-off, the correction can be represented in a model-independent form, with both electron and proton radiation taken into account. Numerical calculations show that the contribution of the proton radiation is not negligible. Overall, at high Q 2 and energies the total correction to µGE/GM grows, but is dominated by TPE. At low energies both TPE and BS may be significant; the latter amounts to ∼ 0.01 for some reasonable cut-off choices.

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“…If hard TPE were properly accounted for, it is possible that the polarization asymmetry and Rosenbluth separation measurements would actually be consistent with each other. Unfortunately, there is no model independent method for calculating hard TPE, though there are numerous model-dependent approaches, such as using hadronic intermediate states [18][19][20], dispersion relations [21][22][23], generalized parton distributions [24], and phenomenological fits [25][26][27]. Many predictions suggest that the inclusion of hard TPE would resolve the form factor discrepancy, while some disagree [28,29].…”

Section: Why Measurementioning

confidence: 99%

The continuing story of two-photon exchange: results from the OLYMPUS experiment

Schmidt¹

2017

Proceedings of 55th International Winter Meeting on Nuclear Physics — PoS(BORMIO2017)

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Over the past two decades, a discrepancy has emerged between two different techniques for measuring the proton's electromagnetic form factors. Unpolarized electron-proton cross section measurements paint a picture of the proton's internal structure that is incompatible with measurements from polarization transfer experiments. The leading hypothesis is that the discrepancy is caused by a typically neglected radiative correction, hard two-photon exchange (TPE), which would affect the two measurement techniques in different ways. There is no model independent way to calculate hard TPE, but it can be measured experimentally by looking for an asymmetry between the positron-proton and electron-proton elastic cross sections. Three recent experiments have attempted to quantify this asymmetry, and, just last month, the third of these, called OLYMPUS, released its results [1]. The OLYMPUS experiment collected data in 2012 at DESY, alternating between 2 GeV electron and positron beams, directed through a hydrogen gas target. The scattered lepton and recoiling proton were detected in coincidence with a large acceptance toroidal spectrometer. The relative luminosity between the two beam species was monitored with three independent systems, and the results comprise 3 inverse fb of integrated luminosity, exceeding by a factor of three the other two TPE experiments combined. In this talk, the case for the TPE hypothesis will be presented, the OLYMPUS experiment will be described, and the results of all three experiments will be compared.

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Two-photon-exchange amplitude withπNintermediate states:P33channel

Cited by 41 publications

References 21 publications

Theoretical constraints and systematic effects in the determination of the proton form factors

Theoretical constraints and systematic effects in the determination of the proton form factors

Radiative corrections to polarization observables in electron-proton scattering

The continuing story of two-photon exchange: results from the OLYMPUS experiment

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