Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Aperture calculation of the Pierre Auger Observatory surface detector   We determine the instantaneous aperture and integrated exposure of the
surface detector of the Pierre Auger Observatory, taking into account the
trigger efficiency as a function of the energy, arrival direction (with zenith
angle lower than 60 degrees) and nature of the primary cosmic-ray. We make use
of the so-called Lateral Trigger Probability function (or LTP) associated with
an extensive air shower, which summarizes all the relevant information about
the physics of the shower, the water tank Cherenkov detector, and the triggers.

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The categories of this paper are: hep-th
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The categories of this paper are: cond-mat
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The categories of this paper are: math
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The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga