Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Kinematic distributions and nuclear effects of $J/\psi$ production in
  920 GeV fixed-target proton-nucleus collisions   Measurements of the kinematic distributions of $J/\psi$ mesons produced in
$p-$C, $p-$Ti and $p-$W collisions at $\sqrt{s}=41.6 \mathrm{GeV}$ in the
Feynman-$x$ region $-0.34 < x_{F} < 0.14$ and for transverse momentum up to
$p_T = 5.4 \mathrm{GeV}/c$ are presented. The $x_F$ and $p_T$ dependencies of
the nuclear suppression parameter, $\alpha$, are also given. The results are
based on $2.4 \cdot 10^{5}$ $J/\psi$ mesons in both the $e^+ e^-$ and
$\mu^{+}\mu^{-}$ decay channels. The data have been collected by the HERA-B
experiment at the HERA proton ring of the DESY laboratory. The measurement
explores the negative region of $x_{F}$ for the first time. The average value
of $\alpha$ in the measured $x_{F}$ region is $0.981 \pm 0.015$. The data
suggest that the strong nuclear suppression of $J/\psi$ production previously
observed at high $x_F$ turns into an enhancement at negative $x_F$.

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The categories of this paper are: comp-gas
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The categories of this paper are: supr-con
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
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The categories of this paper are: q-fin
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The categories of this paper are: econ
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: nlin
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The categories of this paper are: chao-dyn
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The categories of this paper are: eess
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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an