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  • Akiba, Y; Alfred, M; Belmont, R; Berdnikov, Y; Brooks, M L; Butler, C; Campbell, S; V Canoa Roman; Chiu, M; DeBlasio, K; Dehmelt, K; Deshpande, A; Desmond, E J; Dumancic, M; Enokizono, A; Esumi, S; Feege, N; Franz, A; Gal, C; Garg, P; Grau, N; Gunji, T; Hachiya, T; Hahn, K I; Han, S Y; Haseler, T O S; Hemmick, T K; Hill, K; Hodges, A; Hong, B; Huang, J; Isenhower, D; Jacak, B V; Z Ji; Johnson, B M; Jouan, D; Jumper, D S; Kapukchyan, D; Khachatryan, V; Kim, C; Kincses, D; Kistenev, E; Koblesky, T; Kudo, S; Lajoie, J G; Lallow, E O; Lebedev, A; Lewis, N A; Lim, S H; V -R Loggins; Lokos, S; Lynch, D; Malaev, M; Mannel, E; Mignerey, A C; Milov, A; Mitchell, J T; Nagy, M I; Nattrass, C; Nouicer, R; Novák, T; Novotny, R; O'Brien, E; Orjuela Koop, J D; Osborn, J D; Park, J S; Patel, M; Perepelitsa, D V; Pun, A; Radzevich, P V; Riabov, V; Richford, D; Sako, H; Sato, K; Sato, S; Schmoll, B K; Sexton, A; T -A Shibata; Shimomura, M; Silva, C L; Silvermyr, D; Skoby, M J; Slunečka, M; Sorensen, S P; Stankus, P W; Syed, S; Tanida, K; Towell, R S; Tserruya, I; Ujvari, B; Wang, X R; Wong, C P; C Xu; Yanovich, A; Yin, P; Yoon, I; Yushmanov, I E; Zajc, W A; Zharko, S; Zou, L

    arXiv.org, 12/2017
    Paper

    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.