Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Low-$p_T$ $e^{+}e^{-}$ pair production in Au$+$Au collisions at
  $\sqrt{s_{NN}}$ = 200 GeV and U$+$U collisions at $\sqrt{s_{NN}}$ = 193 GeV
  at STAR   We report first measurements of $e^{+}e^{-}$ pair production in the mass
region 0.4 $<M_{ee}<$ 2.6 GeV/$c^{2}$ at low transverse momentum ($p_T<$ 0.15
GeV/$c$) in non-central Au$+$Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and
U$+$U collisions at $\sqrt{s_{NN}}$ = 193 GeV. Significant enhancement factors,
expressed as ratios of data over known hadronic contributions, are observed in
the 40-80% centrality of these collisions. The excess yields peak distinctly at
low-$p_T$ with a width ($\sqrt{\langle p^2_T\rangle}$) between 40 to 60
MeV/$c$. The absolute cross section of the excess depends weakly on centrality
while those from a theoretical model calculation incorporating an in-medium
broadened $\rho$ spectral function and radiation from a Quark Gluon Plasma or
hadronic cocktail contributions increase dramatically with increasing number of
participant nucleons. Model calculations of photon-photon interactions
generated by the initial projectile and target nuclei describe the observed
excess yields but fail to reproduce the $p^{2}_{T}$ distributions.

16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: econ
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
37
The categories of this paper are: supr-con
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The categories of this paper are: q-bio
11
The categories of this paper are: hep-lat