Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hadronic interactions at ultra high energies -- tests with the Pierre
  Auger Observatory   The Pierre Auger Observatory is a hybrid detector for cosmic rays with E >
1EeV. From the gathered data we estimated the proton-proton cross-section at
sqrt(s) = 55 TeV and tested other features of the hadronic interaction models,
which use extrapolations from the LHC energy. The electromagnetic component,
carrying most of the energy of the shower, is precisely measured using
fluorescence telescopes, while the hadronic back- bone of the shower is
indirectly tested by measuring the muons arriving to the surface detector. The
analyses show that models fail to describe these two components consistently,
predicting too few muons at the ground.

21
The categories of this paper are: adap-org
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
29
The categories of this paper are: funct-an