Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of the photon-proton total cross section at a center-of-mass
  energy of 209 GeV at HERA   The photon-proton total cross section has been measured in the process e+ p
-> e+ gamma p -> e+ X with the ZEUS detector at HERA. Events were collected
with photon virtuality Q^2 < 0.02 GeV^2 and average gamma-p center-of-mass
energy W_{gamma p} = 209 GeV in a dedicated run, designed to control systematic
effects, with an integrated luminosity of 49 nb^{-1}. The measured total cross
section is sigma_{tot}^{gamma p} = 174 +- 1 (stat.) +- 13 (syst.) microbarns.
The energy dependence of the cross section is compatible with parameterizations
of high-energy p-p and p-pbar data.

13
The categories of this paper are: quant-ph
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
10
The categories of this paper are: q-bio
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an