Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of the proton-air cross-section at $\sqrt{s}=57$ TeV with
  the Pierre Auger Observatory   We report a measurement of the proton-air cross-section for particle
production at the center-of-mass energy per nucleon of 57 TeV. This is derived
from the distribution of the depths of shower maxima observed with the Pierre
Auger Observatory: systematic uncertainties are studied in detail. Analysing
the tail of the distribution of the shower maxima, a proton-air cross-section
of $[505\pm22(stat)^{+28}_{-36}(sys)]$ mb is found.

33
The categories of this paper are: plasm-ph
31
The categories of this paper are: ao-sci
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
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The categories of this paper are: funct-an
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
5
The categories of this paper are: gr-qc
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The categories of this paper are: hep-lat
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The categories of this paper are: nlin
3
The categories of this paper are: physics
1
The categories of this paper are: cs
4
The categories of this paper are: cond-mat
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The categories of this paper are: nucl-ex
12
The categories of this paper are: nucl-th
27
The categories of this paper are: comp-gas