Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Electromagnetic radiation in heavy ion collisions: Progress and puzzles   We review the current state of photon and dilepton measurements at RHIC,
emphasizing that of the theoretical work seeking to interpret them. We
highlight the progress made recently in the modelling of relativistic nuclear
collisions, and explore the effect on electromagnetic observables. Some
outstanding puzzles are presented.

13
The categories of this paper are: quant-ph
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The categories of this paper are: q-fin
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The categories of this paper are: stat
26
The categories of this paper are: bayes-an
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The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
8
The categories of this paper are: hep-ex
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
1
The categories of this paper are: cs
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The categories of this paper are: hep-th
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The categories of this paper are: hep-lat
4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an