Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: J/psi production at HERA   We consider the J/psi photo-production data collected at HERA in the light of
next-to-leading order predictions for the color-singlet yield and polarization.
We find that, while the shapes of inclusive distributions in the transverse
momentum and inelasticity are well reproduced, the experimental rates are
larger than those given by the color-singlet contribution alone. Furthermore,
the next-to-leading order calculation predicts the J/psi's to be mostly
longitudinally polarized at high transverse momentum in contrast with the trend
of the preliminary data from the ZEUS collaboration.

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The categories of this paper are: patt-sol
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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: hep-th
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The categories of this paper are: hep-lat
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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The categories of this paper are: alg-geom
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The categories of this paper are: cond-mat
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The categories of this paper are: q-fin
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The categories of this paper are: astro-ph
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The categories of this paper are: econ
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The categories of this paper are: stat