Beam normal spin asymmetry in the quasi-RCS approximation

Abstract

The two-photon exchange contribution to the single spin asymmetries with the spin orientation normal to the reaction plane is discussed for elastic electron-proton scattering in the equivalent photon approximation. In this case, hadronic part of the two-photon exchange amplitude describes real Compton scattering (RCS). We show that in the case of the beam normal spin asymmetry, this approximation selects only the photon helicity flip amplitudes of RCS. At low energies, we make use of unitarity and estimate the contribution of the $\pi N$ multipoles to the photon helicity flip amplitudes. In the Regge regime, QRCS approximation allows for a contribution from two pion exchange, and we provide an estimate of such contributions. We furthermore discuss the possibility of the quark and gluon GPD's contributions in the QRCS kinematics.

10 pages, 5 figures, revtex, submitted to Phys. Rev. C; new version: references added

References in corpus (7)

• Proton elastic form factor ratios to $Q^2$ = 3.5 GeV${}^2$ by polarization transfer
• Precision Rosenbluth measurement of the proton elastic form factors
• Measurement of the Transverse Beam Spin Asymmetry in Elastic Electron Proton Scattering and the Inelastic Contribution to the Imaginary Part of the Two-Photon Exchange Amplitude
• Resonance estimates for single spin asymmetries in elastic electron-nucleon scattering
• Collinear Photon Exchange in the Beam Normal Polarization Asymmetry of Elastic Electron-Proton Scattering
• Large Logarithms in the Beam Normal Spin Asymmetry of Elastic Electron--Proton Scattering
• Doubly virtual Compton scattering and the beam normal spin asymmetry

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• New Measurements of the Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering Over a Range of Spin-0 Nuclei
• Target-normal single-spin asymmetry in elastic electron-nucleon scattering
• Beam-normal single-spin asymmetry in elastic scattering of electrons from a spin-0 nucleus
• Measurement of the Beam-Normal Single-Spin Asymmetry for Elastic Electron Scattering from ${}^{12}$C and ${}^{27}$Al
• 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
• Precision Measurement of the Beam-Normal Single-Spin Asymmetry in Forward-Angle Elastic Electron-Proton Scattering
• Two photon exchange in elastic electron scattering off hadronic systems
• Lepton mass effects for beam-normal single-spin asymmetry in elastic muon-proton scattering
• Target normal single-spin asymmetry in inclusive electron-nucleon scattering in the 1/Nc expansion