We present results of analyses of two-pion interferometry in Au+Au collisions at √SNN=7.7, 11.5, 19.6, 27, 39, 62.4, and 200 GeV measured in the STAR detector as part of the BNL Relativistic Heavy Ion Collider Beam Energy Scan program. The extracted correlation lengths (Hanbury-Brown–Twiss radii) are studied as a function of beam energy, azimuthal angle relative to the reaction plane, centrality, and transverse mass (mT) of the particles. The azimuthal analysis allows extraction of the eccentricity of the entire fireball at kinetic freeze-out. The energy dependence of this observable is expected to be sensitive to changes in the equation of state. A new global fit method is studied as an alternate method to directly measure the parameters in the azimuthal analysis. The eccentricity shows a monotonic decrease with beam energy that is qualitatively consistent with the trend from all model predictions and quantitatively consistent with a hadronic transport model.

Document Type


Publication Date


Notes/Citation Information

Published in Physical Review C: Nuclear Physics, v. 92, no. 1, article 014904, p. 1-27.

©2015 American Physical Society

The copyright holder has granted permission for posting the article here.

Collectively the authors are known as the STAR Collaboration. Due to the large number of authors involved, only the first 10 and the ones affiliated with the University of Kentucky are listed in the author section above. For the complete list of authors, please download this article or visit the following link: http://dx.doi.org/10.1103/PhysRevC.92.014904

Digital Object Identifier (DOI)


Funding Information

This work was supported in part by the Offices of NP and HEP within the US DOE Office of Science, the US NSF, CNRS/IN2P3; FAPESP CNPq of Brazil; Ministry of Education and Science of the Russian Federation; NNSFC, CAS, MoST, and MoE of China; the Korean Research Foundation; GA and MSMT of the Czech Republic; FIAS of Germany; DAE, DST, and CSIR of India; National Science Centre of Poland; National Research Foundation of the Republic of Croatia, Ministry of Science, Education and Sports of the Republic of Croatia; and RosAtom of Russia.

Fig 1.png (458 kB)
Figure 1

Fig 2.png (218 kB)
Figure 2

Fig 3.png (76 kB)
Figure 3

Fig 4.png (126 kB)
Figure 4

Fig 5.png (166 kB)
Figure 5

Fig 6.png (73 kB)
Figure 6

Fig 7.png (58 kB)
Figure 7

Fig 8.png (148 kB)
Figure 8

Fig 9.png (129 kB)
Figure 9

Fig 10.png (73 kB)
Figure 10

Fig 11.png (48 kB)
Figure 11

Fig 12.png (129 kB)
Figure 12

Fig 13.png (126 kB)
Figure 13

Fig 14.png (126 kB)
Figure 14

Fig 15.png (119 kB)
Figure 15

Fig 16.png (126 kB)
Figure 16

Fig 17.png (122 kB)
Figure 17

Fig 18.png (126 kB)
Figure 18

Fig 19.png (120 kB)
Figure 19

Fig 20.png (124 kB)
Figure 20

Fig 21.png (120 kB)
Figure 21

Fig 22.png (126 kB)
Figure 22

Fig 23.png (121 kB)
Figure 23

Fig 24.png (126 kB)
Figure 24

Fig 25.png (121 kB)
Figure 25

Fig 26.png (38 kB)
Figure 26

Fig 27.png (90 kB)
Figure 27

Fig 28.png (103 kB)
Figure 28

Table 1.GIF (34 kB)
Table 1