Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Measurement of the Associated $\gamma + \mu^\pm$ Production Cross
  Section in $p \bar p$ Collisions at $\sqrt{s} = 1.8$ TeV   We present the first measurement of associated direct photon + muon
production in hadronic collisions, from a sample of 1.8 TeV $p \bar p$
collisions recorded with the Collider Detector at Fermilab. Quantum
chromodynamics (QCD) predicts that these events are primarily from the Compton
scattering process $cg \to c\gamma$, with the final state charm quark producing
a muon. Hence this measurement is sensitive to the charm quark content of the
proton. The measured cross section of $29\pm 9 pb^{-1}$ is compared to a
leading-order QCD parton shower model as well as a next-to-leading-order QCD
calculation.

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The categories of this paper are: atom-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: econ
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The categories of this paper are: math-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-th
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The categories of this paper are: eess
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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: cond-mat
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The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
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The categories of this paper are: patt-sol
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The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn