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  • Aidala, C; Akiba, Y; Alfred, M; Barish, K. N; Bathe, S; Belmont, R; Berdnikov, Y; Boer, M; Bok, J. S; Butler, C; Campbell, S; Chiu, M; Danley, T. W; DeBlasio, K; Dehmelt, K; Deshpande, A; Do, J. H; Dumancic, M; Enokizono, A; Esumi, S; Feege, N; Franz, A; Gal, C; Garg, P; Grau, N; Gunji, T; Hachiya, T; Haggerty, J. S; Hahn, K. I; Han, S. Y; Haseler, T. O. S; He, X; Hill, K; Hodges, A; Hong, B; Huang, J; Isenhower, D; Jouan, D; Jumper, D. S; Kapukchyan, D; Khachatryan, V; Kim, C; Kim, M. H; Kincses, D; Kistenev, E; Koblesky, T; Kotov, D; Kudo, S; Lallow, E. O; Lebedev, A; Lee, S. H; Lewis, N. A; Li, X; Liu, L. D; Liu, M. X; Loggins, V. -R; Lokos, S; Lynch, D; Makek, M; Malaev, M; Manko, V. I; Mannel, E; Metzger, W. J; Milov, A; Mitchell, J. T; Nattrass, C; Nouicer, R; Novák, T; Novotny, R; O'Brien, E; Patel, M; Pun, A; Purschke, M. L; Riabov, V; Richford, D; Sako, H; Sato, K; Sato, S; Schmoll, B. K; Sexton, A; Shibata, T. -A; Shimomura, M; Silvermyr, D; Slunečka, M; Smith, K. L; Sourikova, I. V; Syed, S; Tanida, K; Tannenbaum, M. J; Towell, C. L; Tserruya, I; Ujvari, B; Wong, C. P; Yamaguchi, Y. L; Yanovich, A; Yin, P; Yoon, I; Zajc, W. A; Zharko, S; Zou, L

    08/2017
    Journal Article

    Phys. Rev. C 96, 064905 (2017) We present measurements of the elliptic flow, $v_2$, as a function of transverse momentum ($p_T$), pseudorapidity ($\eta$), and centrality in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=$200, 62.4, 39, and 19.6 GeV. The beam-energy scan of $d$$+$Au collisions provides a testing ground for the onset of flow signatures in small collision systems. We measure a nonzero $v_2$ signal at all four collision energies, which, at midrapidity and low $p_T$, is consistent with predictions from viscous hydrodynamic models. Comparisons with calculations from parton transport models (based on the {\sc ampt} Monte Carlo generator) show good agreement with the data at midrapidity to forward ($d$-going) rapidities and low $p_T$. At backward (Au-going) rapidities and $p_T>1.5$ GeV/$c$, the data diverges from {\sc ampt} calculations of $v_2$ relative to the initial geometry, indicating the possible dominance of nongeometry related correlations, referred to as nonflow. We also present measurements of the charged-particle multiplicity ($dN_{\rm ch}/d\eta$) as a function of $\eta$ in central $d$$+$Au collisions at the same energies. We find that in $d$$+$Au collisions at $\sqrt{s_{_{NN}}}=$200 GeV the $v_2$ scales with $dN_{\rm ch}/d\eta$ over all $\eta$ in the PHENIX acceptance. At $\sqrt{s_{_{NN}}}=$62.4, and 39 GeV, $v_2$ scales with $dN_{\rm ch}/d\eta$ at midrapidity and forward rapidity, but falls off at backward rapidity. This departure from the $dN_{\rm ch}/d\eta$ scaling may be a further indication of nonflow effects dominating at backward rapidity.