Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of $J/\psi$ pair production in pp collisions at $\sqrt{s}=7
  TeV$   The production of $J/\psi$ pairs in proton-proton collisions at a
centre-of-mass energy of 7 TeV has been observed using an integrated luminosity
of $37.5 pb^{-1}$ collected with the LHCb detector. The production
cross-section for pairs with both \jpsi in the rapidity range
$2<y^{J/\psi}<4.5$ and transverse momentum $p_{T}^{J/\psi}<10 GeV/c$ is $$
\sigma^{J/\psi J/\psi} = 5.1\pm1.0\pm1.1 nb,$$ where the first uncertainty is
statistical and the second systematic.

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The categories of this paper are: hep-ph
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
19
The categories of this paper are: eess
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th