Two-photon exchange corrections to elastic electron-proton scattering at large momentum transfer within the SCET approach

Kivel, N.; Vanderhaeghen, Marc

doi:10.1007/jhep04(2013)029

Cited by 45 publications

(32 citation statements)

References 89 publications

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“…Many model-dependent calculations of TPE have been made (see, for example, Refs. [7][8][9], and others), and these provide a valuable guide for interpreting experimental results. However, rather than adopt any model or calculation framework, I propose a method of estimating the TPE contribution necessary to resolve the form factor discrepancy from form factor data alone, relying on three reasonable assumptions:…”

Section: Introductionmentioning

confidence: 99%

How much two-photon exchange is needed to resolve the proton form factor discrepancy?

Schmidt¹

2020

J. Phys. G: Nucl. Part. Phys.

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Background: One possible explanation for the proton form factor discrepancy is a contribution to the elastic electron-proton cross section from hard two-photon exchange (TPE), a typically neglected radiative correction. Hard TPE cannot be calculated in a model-independent way, but it can be determined experimentally by looking for deviations from unity in the ratio of positron-proton to electron-proton cross sections. Three recent experiments have measured this cross section ratio to quantify hard TPE.Purpose: To interpret the results of these experiments, it is germane to ask: "How large of a deviation from unity is necessary to fully resolve the form factor discrepancy?"Method: I derive an expression using a minimal set of assumptions to answer this question based on global fits to unpolarized and polarized elastic scattering data.Results: I find wide variation when using different global fits, implying that the magnitude of the form factor discrepancy is not well-constrained.Conclusions: Recent measurements of hard TPE can easily accommodate the hypothesis that TPE underlies the proton form factor discrepancy.

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Section: Introductionmentioning

confidence: 99%

How much two-photon exchange is needed to resolve the proton form factor discrepancy?

Schmidt¹

2020

J. Phys. G: Nucl. Part. Phys.

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“…In the "quark" approach, as its name suggests, the nucleon is viewed as an ensemble of quarks (partons), interacting according to QCD [10][11][12][13]. Naturally, the applicability of this approach is limited to the high-Q 2 region.…”

Section: Introductionmentioning

confidence: 99%

Two-photon-exchange amplitude withπNintermediate states:P33channel

Borisyuk

Kobushkin

2014

Phys. Rev. C

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We consider two-photon exchange (TPE) in the elastic electron-proton scattering and evaluate the effect of πN (pion + nucleon) intermediate hadronic states. Among different πN states, we concentrate on the P33 channel; thus we effectively include ∆(1232) resonance with realistic width and shape and corresponding background as well. In agreement with the previous result, obtained for the zero-width resonance, we observe that the TPE correction to the electric form factor is the largest one; it grows with Q 2 and at Q 2 > ∼ 2.5 GeV 2 exceeds the corresponding elastic contribution.

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“…With a real photon at wide angle regime [1], RCS provides access to the high-t transverse structure of the hadron, whereas deep virtual Compton scattering (DVCS) provides access mostly to the high-Q 2 low-t structure. For RCS on proton, the hard scale is reached when the Mandelstam variables s, -t, and -u are larger than the proton mass.…”

Section: Physics Motivation and Preliminary Resultsmentioning

confidence: 99%

Investigating the proton structure through polarization transfers in real Compton scattering processes at JLAB

Fanelli

Cisbani

Hamilton

et al. 2014

EPJ Web of Conferences

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Abstract. In the present work, preliminary results of the analysis of polarization transfers in real Compton scattering (RCS) performed in Hall-C at JLAB are presented, for data collected at large scattering angle ( cm =70 o ) in the experiment E07-002. A previous experiment, E99-114, has already demonstrated a complete inconsistence of its results with a pQCD mechanism at JLAB energy regime. This kind of experiment, therefore, is of crucial importance for understanding the nature of the reaction mechanism for such a simple process, involving a real photon. Furthermore, RCS experiments allow the extraction of Compton form factors and Generalized Parton Distributions (GPDs), the latter connected to the total angular momentum of the nucleon. Physics motivation and preliminary resultsReal Compton scattering (RCS) in the hard scattering limit is a powerful probe of the structure of the nucleon. With a real photon at wide angle regime [1], RCS provides access to the high-t transverse structure of the hadron, whereas deep virtual Compton scattering (DVCS) provides access mostly to the high-Q 2 low-t structure. For RCS on proton, the hard scale is reached when the Mandelstam variables s, -t, and -u are larger than the proton mass. Under such conditions the transition amplitude is expected to factorize as T if (s,t) = f ⊗ K(s,t) ⊗ i , where K(s,t) is the perturbative hard scattering amplitude, involving the coupling of the external photons to the active quarks, and the 's are the soft initial and final wave functions, describing the coupling of the active quarks to the proton. Two different approaches are usually taken as a reference in the interpretation of the results: the "handbag" mechanism [2,3], which involves only one active constituent ( Fig. 1 (left)), with the soft physics for the coupling of this active quark to the proton described in the Generalized Parton Distributions (GPD's) [4,5], and the "perturbative QCD" (pQCD) mechanism [6], in which all three valence quarks are active participants in the hard subprocess, the latter effected by the exchange of two hard gluons ( Fig. 1 (right)), with the soft physics contained in the valence quark distribution. In principle, both mechanisms contribute to a

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Two-photon exchange corrections to elastic electron-proton scattering at large momentum transfer within the SCET approach

Cited by 45 publications

References 89 publications

How much two-photon exchange is needed to resolve the proton form factor discrepancy?

How much two-photon exchange is needed to resolve the proton form factor discrepancy?

Two-photon-exchange amplitude withπNintermediate states:P33channel

Investigating the proton structure through polarization transfers in real Compton scattering processes at JLAB

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