Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Determination of $\pi\pi$ scattering lengths from measurement of
  $\pi^+\pi^-$ atom lifetime   The DIRAC experiment at CERN has achieved a sizeable production of
$\pi^+\pi^-$ atoms and has significantly improved the precision on its lifetime
determination. From a sample of 21227 atomic pairs, a 4% measurement of the
S-wave $\pi\pi$ scattering length difference $|a_0-a_2| =
(.0.2533^{+0.0080}_{-0.0078}|_\mathrm{stat}.{}^{+0.0078}_{-0.0073}|_\mathrm{syst})M_{\pi^+}^{-1}$
has been attained, providing an important test of Chiral Perturbation Theory.

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The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
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The categories of this paper are: econ
9
The categories of this paper are: nlin
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-th
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The categories of this paper are: stat
3
The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: dg-ga
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The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: plasm-ph
34
The categories of this paper are: chem-ph