Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Particle physics @ $\sqrt{s_{pp}}$ > 50 TeV with the Pierre Auger
  Observatory   The Pierre Auger Observatory in Argentina provides the largest data sample of
the cosmic ray events with energy above 10$^{18}$ eV. These high energy events
can be used to test our understanding of the hadronic interactions at energies
beyond the reach of colliders and to probe the basic properties of these
interactions such as the inelastic cross-section of proton-air collisions. The
combination of an array of surface detectors and the fluorescence telescopes of
the Pierre Auger Observatory reduces significantly the dependency of the shower
energy estimation on MC simulations. Despite that, the interpretation of mass
sensitive quantities such as the shower maximum in terms of chemical
composition of cosmic rays still depends on the hadronic interaction models.
This contribution describes the main results of the observatory concerning the
chemical composition of the cosmic rays and focuses on the problem of muon
deficit in hadronic interaction models and on the estimation of proton-air
cross-section from air-shower data.

24
The categories of this paper are: dg-ga
4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
2
The categories of this paper are: math
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg