Document Type

Article

Department/Program

Physics

Journal Title

Physical Review Letters

Pub Date

Fall 9-8-2020

Publisher

American Physical Society

Volume

125

Issue

11

Journal Article URL

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.112502

First Page

112502

Abstract

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 theta_lab = 7.9 degrees 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 (theta_lab -> 0) where they should be most reliable.

DOI

https://doi.org/10.1103/PhysRevLett.125.112502

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