Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hybrid Performance of the Pierre Auger Observatory and Reconstruction of
  Hybrid Events   The Pierre Auger Observatory is a``hybrid'' UHECR detector. The surface
detector (SD) and air fluorescence detector (FD) of the observatory are
designed for observation of cosmic ray showers in coincidence, with a 10% duty
cycle. The resulting data are expected to be superior in quality to those of
either the SD or FD operating individually. Hybrid operation, triggering, data
acquisition, and event reconstruction were successfully demonstrated during the
prototype phase of the project. This paper focuses on 75 hybrid events recorded
during a four month period of running with the prototype detectors in late 2001
and early 2002. The geometric technique for reconstruction of the hybrid events
is described and its advantages over the traditional FD-only method are
demonstrated. A lateral distribution for the water Cherenkov signals, derived
from these data, is presented.

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The categories of this paper are: dg-ga
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: econ
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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: plasm-ph
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The categories of this paper are: quant-ph