Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: First measurement of the rho spectral function in nuclear collisions   The NA60 experiment has studied low-mass muon pairs in 158 AGeV Indium-Indium
collisions at the CERN SPS. A strong excess of pairs is observed above the
expectation from neutral meson decays. The unprecedented sample size of 360 000
events and the good mass resolution of about 2% allow to isolate the excess by
subtraction of the known sources. The shape of the resulting mass spectrum is
consistent with a dominant contribution from pi+ pi- -> rho -> mu+ mu-
annihilation. The associated rho spectral function shows a strong broadening,
but essentially no shift in mass.

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The categories of this paper are: atom-ph
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The categories of this paper are: supr-con
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: chem-ph
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The categories of this paper are: econ
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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: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: math-ph
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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: math