Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pion Freeze-Out Time in Pb+Pb Collisions at 158 A GeV/c Studied via
  pi-/pi+ and K-/K+ Ratios   The effect of the final state Coulomb interaction on particles produced in
Pb+Pb collisions at 158 A GeV/c has been investigated in the WA98 experiment
through the study of the pi-/pi+ and K-/K+ ratios measured as a function of
transverse mass. While the ratio for kaons shows no significant transverse mass
dependence, the pi-/pi+ ratio is enhanced at small transverse mass values with
an enhancement that increases with centrality. A silicon pad detector located
near the target is used to estimate the contribution of hyperon decays to the
pi-/pi+ ratio. The comparison of results with predictions of the RQMD model in
which the Coulomb interaction has been incorporated allows to place constraints
on the time of the pion freeze-out.

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The categories of this paper are: quant-ph
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The categories of this paper are: q-bio
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The categories of this paper are: q-alg
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The categories of this paper are: mtrl-th
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The categories of this paper are: q-fin
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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ex
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The categories of this paper are: cs
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc