Abstract
We estimate the target-normal single-spin asymmetry at nearly forward angles in elastic electron-nucleon scattering. In the leading-order approximation, this asymmetry is proportional to the imaginary part of the two-photon exchange (TPE) amplitude, which can be expressed as an integral over the doubly virtual Compton scattering (VVCS) tensor. We develop a model that parametrizes the VVCS tensor for the case of nearly forward scattering angles. Our parametrization ensures a proper normalization of the imaginary part of the TPE amplitude on the well-known forward limit expression, which is given in terms of nucleon structure functions measurable in inelastic electron-nucleon scattering experiments. We discuss applicability limits of our theory and provide target-normal single-spin asymmetry predictions for both elastic electron-proton and electron-neutron scattering.
Highlights
Elastic lepton scattering off of a nucleon provides a great deal of information on the structure of the hadron
Neglecting higher-order effects, this asymmetry is provided by the interference between one- and two-photon exchange amplitudes
We have constructed the respective inelastic VVCS tensor that can be used in the kinematical region characterized by the Q2 ≪ s condition
Summary
Elastic lepton scattering off of a nucleon (lÆN → lÆN) provides a great deal of information on the structure of the hadron. Unlike the dispersive part of the TPE amplitude, the corresponding imaginary (absorptive) part manifests itself in polarized scattering measurements It can be directly accessed through the analysis of a singlespin asymmetry (SSA) observable in elastic lepton-nucleon scattering, when either the beam or target is polarized in the direction normal to the lepton scattering plane. In that paper the authors explain why the transverse SSA must be zero in the Born approximation by considering electron scattering on a polarized proton target They have shown that the leading-order contribution to such an asymmetry is generated by the absorptive part of the TPE amplitude, which, in its turn, has drawn a significant theoretical interest in recent years.
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