Elastic scattering of electrons and positrons from protons

Hartwig, Sabina; Heimlich, F. H.; Huber, G.; Rössle, E.; Köbberling, M.; Moritz, J.; Schmidt, K.; Wegener, D.; Zeller, D.; Bleckwenn, J.

doi:10.1007/bf02784666

Cited by 18 publications

(15 citation statements)

References 4 publications

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“…There have been several attempts to measure TPE corrections from the ratio of positron scattering to electron scattering cross sections. These include several experiments in the 1960's and 1970's [66,[96][97][98][99][100][101][102][103]. These experiments showed no significant TPE effect, and will be discussed in Section 3.3.…”

Section: Direct Measurements Of Tpe Corrections To σ Rmentioning

confidence: 99%

“…Following Yount et al [96], a series of eight more electron-positron experiments were conducted over the next 13 years using much the same technique. These included experiments at the Stanford Mark III accelerator [97], the Cornell Synchrotron [98,100,101], DESY [99,103], the Orsay Linear Accelerator [102], and SLAC [66]. The results of these experiments are shown in Fig.…”

Section: Early Measurements Of Tpementioning

confidence: 99%

“…3.9 with an additional point from the CLAS TPE test-run experiment [95] (black open square). The open green circles show the previous world data [66,96,97,99,101,103] From this fit, δ γγ was determined as a function of ε and applied as a correction to the reduced crosssection data of Andivahis et al [124] according to Eq. (2.23).…”

Section: The Clas Experimentsmentioning

confidence: 99%

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Two-photon exchange in elastic electron–proton scattering

Afanasev

Blunden

Hasell

et al. 2017

Progress in Particle and Nuclear Physics

100

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We review recent theoretical and experimental progress on the role of two-photon exchange (TPE) in electron-proton scattering at low to moderate momentum transfers. We make a detailed comparison and analysis of the results of competing experiments on the ratio of e + p to e − p elastic scattering cross sections, and of the theoretical calculations describing them. A summary of the current experimental situation is provided, along with an outlook for future experiments.

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Section: Direct Measurements Of Tpe Corrections To σ Rmentioning

confidence: 99%

Section: Early Measurements Of Tpementioning

confidence: 99%

Section: The Clas Experimentsmentioning

confidence: 99%

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Two-photon exchange in elastic electron–proton scattering

Afanasev

Blunden

Hasell

et al. 2017

Progress in Particle and Nuclear Physics

100

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“…Because the one-photon exchange cross section depends quadratically on the lepton charge, the difference between electronnucleon and positron-nucleon cross sections is a test for two-or multi-photon exchange processes. Early comparisons of electron-and positron-nucleon scattering cross sections were consistent with equal cross sections [11,12], but the precision achieved in those early investigations could not exclude two-photon exchange effects at the few percent level of the cross section. Contributions of this size can be expected due to the additional electromagnetic coupling in the two-photon exchange diagram, which brings in a suppression factor α = e 2 /(4π) ≃ 1/137.…”

Section: Introductionmentioning

confidence: 99%

Two-Photon Physics in Hadronic Processes

Carlson

Vanderhaeghen

2007

Annu. Rev. Nucl. Part. Sci.

161

173

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Two-photon exchange contributions to elastic electron-scattering are reviewed. The apparent discrepancy in the extraction of elastic nucleon form factors between unpolarized Rosenbluth and polarization transfer experiments is discussed, as well as the understanding of this puzzle in terms of two-photon exchange corrections. Calculations of such corrections both within partonic and hadronic frameworks are reviewed. In view of recent spin-dependent electron scattering data, the relation of the two-photon exchange process to the hyperfine splitting in hydrogen is critically examined. The imaginary part of the two-photon exchange amplitude as can be accessed from the beam normal spin asymmetry in elastic electron-nucleon scattering is reviewed. Further extensions and open issues in this field are outlined.

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“…Early measurements comparing electron and positron elastic-scattering cross sections [42][43][44][45][46][47][48][49][50] were largely limited to low Q 2 and/or high ε, where calculations [51][52][53] suggest that TPE contributions are small. Given the limited experimental sensitivity of these early measurements, none of the experiments observed a significant deviation from R 2γ = 1.…”

Section: Introductionmentioning

confidence: 99%

Measurement of two-photon exchange effect by comparing elastic e±p cross sections

Rimal¹,

Adikaram²,

Raue³

et al. 2017

Phys. Rev. C

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Measurement of two-photon exchange effect by comparing elastic e ± p cross sections Background: The electromagnetic form factors of the proton measured by unpolarized and polarized electron scattering experiments show a significant disagreement that grows with the squared four momentum transfer (Q 2 ). Calculations have shown that the two measurements can be largely reconciled by accounting for the contributions of two-photon exchange (TPE). TPE effects are not typically included in the standard set of radiative corrections since theoretical calculations of the TPE effects are highly model dependent, and, until recently, no direct evidence of significant TPE effects has been observed. Purpose:We measured the ratio of positron-proton to electron-proton elastic-scattering cross sections in order to determine the TPE contribution to elastic electron-proton scattering and thereby resolve the proton electric form factor discrepancy.Methods: We produced a mixed simultaneous electron-positron beam in Jefferson Lab's Hall B by passing the 5.6 GeV primary electron beam through a radiator to produce a bremsstrahlung photon beam and then passing the photon beam through a convertor to produce electron/positron pairs. The mixed electron-positron (lepton) beam with useful energies from approximately 0.85 to 3.5 GeV then struck a 30-cm long liquid hydrogen (LH2) target located within the CEBAF Large Acceptance Spectrometer (CLAS). By detecting both the scattered leptons and the recoiling protons we identified and reconstructed elastic scattering events and determined the incident lepton energy. A detailed description of the experiment is presented.Results: We present previously unpublished results for the quantity R2γ, the TPE correction to the elasticscattering cross section, at Q 2 ≈ 0.85 and 1.45 GeV 2 over a large range of virtual photon polarization ε. Conclusions:Our results, along with recently published results from VEPP-3, demonstrate a non-zero contribution from TPE effects and are in excellent agreement with the calculations that include TPE effects and largely reconcile the form-factor discrepancy up to Q 2 ≈ 2 GeV 2 . These data are consistent with an increase in R2γ with decreasing ε at Q 2 ≈ 0.85 and 1.45 GeV 2 . There are indications of a slight increase in R2γ with Q 2 .

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Elastic scattering of electrons and positrons from protons

Cited by 18 publications

References 4 publications

Two-photon exchange in elastic electron–proton scattering

Two-photon exchange in elastic electron–proton scattering

Two-Photon Physics in Hadronic Processes

Measurement of two-photon exchange effect by comparing elastic e±p cross sections

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