Evidence for two-photon exchange contributions in electron-proton and positron-proton elastic scattering

Abstract

The comparison of positron-proton and electron-proton elastic scattering cross sections is a sensitive test for the presence of two-photon exchange contributions. Thirty years ago, positron data were considered adequate to set tight limits on the size of two-photon corrections. More recently, these radiative corrections have again become a matter of great interest as a possible explanation for the discrepancy between Rosenbluth and polarization transfer measurements of the proton electromagnetic form factors. We have reexamined the electron and positron scattering data to see if they can accommodate two-photon effects of the size necessary to account for the Rosenbluth-polarization transfer discrepancy. The data are consistent with simple estimates of the two-photon contributions necessary to explain the discrepancy. In fact, they strongly favor a large epsilon-dependent correction to the positron to electron ratio, providing the first direct experimental evidence for a two-photon contribution to unpolarized lepton-proton scattering.

5 pages, 3 figures, submitted to PRC. Fixed typos

References in corpus (3)

• Two-photon exchange and elastic electron-proton scattering
• How to reconcile the Rosenbluth and the polarization transfer method in the measurement of the proton form factors
• How well do we know the electromagnetic form factors of the proton?

Cited by in corpus (45)

• Global analysis of proton elastic form factor data with two-photon exchange corrections
• Two-photon exchange in elastic electron-nucleon scattering
• Nucleon electromagnetic form factors
• Nucleon Form Factors in QCD
• Review of two-photon exchange in electron scattering
• Extraction of the proton radius from electron-proton scattering data
• Electromagnetic Form Factors of the Nucleon and Compton Scattering
• Two-Photon Physics in Hadronic Processes
• Proton and neutron electromagnetic form factors and uncertainties
• $\Delta$ resonance contribution to two-photon exchange in electron-proton scattering
• Measurement of the two-photon exchange contribution to the elastic $e^{\pm }p$ scattering cross sections at the VEPP-3 storage ring
• Two-photon exchange in elastic electron-proton scattering
• Re-analysis of the nucleon space- and time-like electromagnetic form factors in a two-component model
• The SAMPLE Experiment and Weak Nucleon Structure
• Low Q^2 measurements of the proton form factor ratio $m{u}_p{G}_E/G_M$
• Towards a resolution of the proton form factor problem: new electron and positron scattering data
• Search for effects beyond the Born approximation in polarization transfer observables in $\vec{e}p$ elastic scattering
• Polarization Transfer Observables in Elastic Electron Proton Scattering at $Q^2=$2.5, 5.2, 6.8, and 8.5 GeV${}^2$
• Proton G_E/G_M from beam-target asymmetry
• Electromagnetic form factors of the nucleon: new fit and analysis of uncertainties
• Extraction of two-photon contributions to the proton form factors
• Flavor decomposition of the nucleon electromagnetic form factors
• Experimental constraints on non-linearities induced by two-photon effects in elastic and inelastic Rosenbluth separations
• Measurement of two-photon exchange effect by comparing elastic $e^{\pm }p$ cross sections
• The Proton Elastic Form Factor Ratio at Low Momentum Transfer
• Nucleon Form Factors - A Jefferson Lab Perspective
• Search for a Two-Photon Exchange Contribution to Inclusive Deep-Inelastic Scattering
• Reexamination of phenomenological two-photon exchange corrections to the proton form factors and e+-p scattering
• Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR
• Coulomb distortion in high-Q^2 elastic e-p scattering
• $\Delta (1232)$ Resonance Contribution to Two-Photon Exchange in Electron-Proton Scattering Revisited
• Form Factors and Two-Photon Exchange in High-Energy Elastic Electron-Proton Scattering
• Demonstration of a novel technique to measure two-photon exchange effects in elastic $e^{\pm }p$ scattering
• Two-Photon Exchange Effect Studied with Neural Networks
• Phenomenological extraction of two-photon exchange amplitudes from elastic electron-proton scattering cross section data
• Ratio of ${\sigma }_L/{\sigma }_T$ for $p(e,e^{\prime }{K}^{+})\Lambda$ Extracted from Polarization Transfer
• Up- and Down-Quark Contributions to the Nucleon Form Factors
• The ratio of $e^{\pm }p$ scattering cross sections predicted from the global fit of elastic $ep$ data
• Study of Two-Photon Exchange via the Beam Transverse Single Spin Asymmetry in Electron-Proton Elastic Scattering at Forward Angles over a Wide Energy Range
• Measurement of the 12C(e,e'p)11B Two-Body Breakup Reaction at High Missing Momentum Values
• Radiative corrections to elastic proton-electron scattering measured in coincidence
• Resonances contribution to two-photon exchange effects and possible large forward-backward asymmetry in $e^{+}{e}^{-}\to p\bar{p}$
• Super-Rosenbluth Measurements with Electrons and Positrons
• A measurement of two-photon exchange in Super-Rosenbluth separations with positron beams
• Unpolarized nucleon structure studies utilizing polarized electromagnetic probes