Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Elliptic flow of electrons from heavy-flavor hadron decays in Au+Au
  collisions at $\sqrt{s_{\rm NN}} = $ 200, 62.4, and 39 GeV   We present measurements of elliptic flow ($v_2$) of electrons from the decays
of heavy-flavor hadrons ($e_{HF}$) by the STAR experiment. For Au+Au collisions
at $\sqrt{s_{\rm NN}} = $ 200 GeV we report $v_2$, for transverse momentum
($p_T$) between 0.2 and 7 GeV/c using three methods: the event plane method
($v_{2}${EP}), two-particle correlations ($v_2${2}), and four-particle
correlations ($v_2${4}). For Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 62.4 and
39 GeV we report $v_2${2} for $p_T< 2$ GeV/c. $v_2${2} and $v_2${4} are
non-zero at low and intermediate $p_T$ at 200 GeV, and $v_2${2} is consistent
with zero at low $p_T$ at other energies. The $v_2${2} at the two lower beam
energies is systematically lower than at $\sqrt{s_{\rm NN}} = $ 200 GeV for
$p_T < 1$ GeV/c. This difference may suggest that charm quarks interact less
strongly with the surrounding nuclear matter at those two lower energies
compared to $\sqrt{s_{\rm NN}} = 200$ GeV.

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The categories of this paper are: hep-th
1
The categories of this paper are: cs
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
0
The categories of this paper are: hep-ph
3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
35
The categories of this paper are: mtrl-th
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat