L. Adamczyk, AGH University of Science and Technology, Poland
J. R. Adams, Ohio State University
James K. Adkins, University of KentuckyFollow
G. Agakishiev, Joint Institute for Nuclear Research, Russia
M. M. Aggarwal, Panjab University, India
Z. Ahammed, Variable Energy Cyclotron Centre, India
N. N. Ajitanand, State University of New York - Stony Brook
I. Alekseev, Alikhanov Institute for Theoretical and Experimental Physics, Russia
D. M. Anderson, Texas A&M University
R. Aoyama, University of Tsukuba, Japan
A. Aparin, Joint Institute for Nuclear Research, Russia
D. Arkhipkin, Brookhaven National Laboratory
E. C. Aschenauer, Brookhaven National Laboratory
M. U. Ashraf, Tsinghua University, China
A. Attri, Panjab University, India
G. S. Averichev, Joint Institute for Nuclear Research, Russia
X. Bai, Central China Normal University, China
V. Bairathi, National Institute of Science Education and Research, India
K. Barish, University of California - Riverside
A. Behera, State University of New York - Stony Brook
R. Bellwied, University of Houston
A. Bhasin, University of Jammu, India
A. K. Bhati, Panjab University, India
P. Bhattarai, The University of Texas at Austin
J. Bielcik, Czech Technical University in Prague, Czech Republic
J. Bielcikova, Nuclear Physics Institute ASCR, Czech Republic
L. C. Bland, Brookhaven National Laboratory
I. G. Bordyuzhin, Alikhanov Institute for Theoretical and Experimental Physics, Russia
J. Bouchet, Kent State University
J. D. Brandenburg, Rice University
Renee H. Fatemi, University of KentuckyFollow
Suvarna Ramachandran, University of KentuckyFollow


The azimuthal anisotropic flow of identified and unidentified charged particles has been systematically studied in Cu+Au collisions at √sNN = 200 GeV for harmonics n = 1–4 in the pseudorapidity range |η| < 1. The directed flow in Cu+Au collisions is compared with the rapidity-odd and, for the first time, the rapidity-even components of charged particle directed flow in Au+Au collisions at √sNN = 20 GeV. The slope of the directed flow pseudorapidity dependence in Cu+Au collisions is found to be similar to that in Au+Au collisions, with the intercept shifted toward positive pseudorapidity values, i.e., the Cu-going direction. The mean transverse momentum projected onto the spectator plane ⟨px⟩ in Cu+Au collision also exhibits approximately linear dependence on pseudorapidity with the intercept at about η ≈ −0.4 (shifted from zero in the Au-going direction), closer to the rapidity of the Cu+Au system center of mass. The observed dependencies find a natural explanation in a picture of the directed flow originating partly due the “tilted source” and partly due to the asymmetry in the initial density distribution. A charge dependence of ⟨px⟩ was also observed in Cu+Au collisions, consistent with an effect of the initial electric field created by charge difference of the spectator protons in two colliding nuclei. The rapidity-even component of directed flow in Au+Au collisions is close to that in Pb+Pb collisions at √sNN = 2.76 TeV, indicating a similar magnitude of dipolelike fluctuations in the initial-state density distribution. Higher harmonic flow in Cu+Au collisions exhibits similar trends to those observed in Au+Au and Pb+Pb collisions and is qualitatively reproduced by a viscous hydrodynamic model and a multiphase transport model. For all harmonics with n ≥ 2 we observe an approximate scaling of vn with the number of constituent quarks; this scaling works as well in Cu+Au collisions as it does in Au+Au collisions.

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Published in Physical Review C, v. 98, issue 1, 014915, p. 1-22.

©2018 American Physical Society

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Due to the large number of authors, only the first 30 and the authors 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:

This group of authors is collectively known as the STAR Collaboration.

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This work was supported in part by the Office of Nuclear Physics within the US DOE Office of Science, the US National Science Foundation, the Ministry of Education and Science of the Russian Federation, National Natural Science Foundation of China, Chinese Academy of Science, the Ministry of Science and Technology of China and the Chinese Ministry of Education, the National Research Foundation of Korea, Czech Science Foundation and Ministry of Education, Youth and Sports of the Czech Republic, Department of Atomic Energy and Department of Science and Technology of the Government of India, the National Science Centre of Poland, the Ministry of Science, Education and Sports of the Republic of Croatia, RosAtom of Russia and German Bundesministerium fur Bildung, Wissenschaft, Forschung and Technologie (BMBF), and the Helmholtz Association.