Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Pierre Auger Cosmic Ray Observatory   The Pierre Auger Observatory, located on a vast, high plain in western
Argentina, is the world's largest cosmic ray observatory. The objectives of the
Observatory are to probe the origin and characteristics of cosmic rays above
$10^{17}$ eV and to study the interactions of these, the most energetic
particles observed in nature. The Auger design features an array of 1660
water-Cherenkov particle detector stations spread over 3000 km$^2$ overlooked
by 24 air fluorescence telescopes. In addition, three high elevation
fluorescence telescopes overlook a 23.5 km$^2$, 61-detector infilled array with
750 m spacing. The Observatory has been in successful operation since
completion in 2008 and has recorded data from an exposure exceeding 40,000
km$^2$ sr yr. This paper describes the design and performance of the detectors,
related subsystems and infrastructure that make up the Auger Observatory.

11
The categories of this paper are: hep-lat
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
25
The categories of this paper are: patt-sol
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
7
The categories of this paper are: hep-th
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph