Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of the prompt $J/\psi$ pair production cross-section in $pp$
  collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector   The production of two prompt $J/\psi$ mesons, each with transverse momenta
$p_{\mathrm{T}}>8.5$ GeV and rapidity $|y| < 2.1$, is studied using a sample of
proton-proton collisions at $\sqrt{s} = 8$ TeV, corresponding to an integrated
luminosity of 11.4 fb$^{-1}$ collected in 2012 with the ATLAS detector at the
LHC. The differential cross-section, assuming unpolarised $J/\psi$ production,
is measured as a function of the transverse momentum of the
lower-$p_{\mathrm{T}}$ $J/\psi$ meson, di-$J/\psi$ $p_{\mathrm{T}}$ and mass,
the difference in rapidity between the two $J/\psi$ mesons, and the azimuthal
angle between the two $J/\psi$ mesons. The fraction of prompt pair events due
to double parton scattering is determined by studying kinematic correlations
between the two $J/\psi$ mesons. The total and double parton scattering
cross-sections are compared with predictions. The effective cross-section of
double parton scattering is measured to be $\sigma_{\mathrm{eff}} = 6.3 \pm 1.6
\mathrm{(stat)} \pm 1.0 \mathrm{(syst)}$ mb.

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The categories of this paper are: astro-ph
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The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
4
The categories of this paper are: cond-mat
7
The categories of this paper are: hep-th
20
The categories of this paper are: acc-phys
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The categories of this paper are: gr-qc
31
The categories of this paper are: ao-sci
12
The categories of this paper are: nucl-th
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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: quant-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex