Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Event geometrical anisotropy and fluctuation viewed by HBT
  interferometry   Azimuthal angle dependence of the pion source radii was measured applying the
event shape selection at the PHENIX experiment. The measured final source
eccentricity is found to be enhanced when selecting events with higher
magnitude of the second-order flow vector, as well as the elliptic flow
coefficient $v_{2}$. The spatial twist of the particle-emitting source was also
explored using a transport model. Results indicate a possible twisted source in
the final state due to the initial longitudinal fluctuations.

23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
5
The categories of this paper are: gr-qc
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
29
The categories of this paper are: funct-an