Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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 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.

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The categories of this paper are: chem-ph
27
The categories of this paper are: comp-gas
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
6
The categories of this paper are: astro-ph
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
4
The categories of this paper are: cond-mat
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph