engleski

Precision Measurement of the Beam-Normal Single-Spin Asymmetry in Forward-Angle Elastic Electron-Proton Scattering

A beam-normal single-spin asymmetry generated in the scattering of transversely polarized electrons from unpolarized nucleons is an observable related to the imaginary part of the two-photon exchange process. We report a 2% precision measurement of the beam-normal single-spin asymmetry in elastic electron- proton scattering with a mean scattering angle of θlab=7.9° and a mean energy of 1.149 GeV. The asymmetry result is B n = − 5.194 ± 0.067 ( stat ) ± 0.082 (syst) ppm. This is the most precise measurement of this quantity available to date and therefore provides a stringent test of two- photon exchange models at far-forward scattering angles ( θ lab → 0 ) where they should be most reliable.

beam-normalization, single-spin asymmetry, scattering, transversaly polarized electrons, unpolarized nucleons

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