Abstract
We have measured the p t -integrated quadrupole component of two-particle azimuth correlations (related to quantity v 2, denoted in this case by v 2{2D}) via two-dimensional (2D) angular autocorrelations on (η,φ) for unidentified hadrons in Au-Au collisions at 62 and 200 GeV. The 2D autocorrelation provides a method to remove non-quadrupole contributions to v 2 (conventionally termed “nonflow”) under the assumption that such processes produce significant dependence on pair-wise relative η within the detector acceptance. We hypothesize, based on empirical observations, that non-quadrupole contributions are dominated by minijets or minimum-bias jets. Using the optical Glauber eccentricity model for initial-state geometry we find simple and accurate universal energy and centrality trends for the quadrupole component. Centrality trends are determined only by the initial state (impact parameter b and center-of-mass energy \(\sqrt{s_{\mathit{NN}}}\) ). There is no apparent dependence on evolving system dynamics (e.g., equation of state or number of secondary collisions). Our measurements of the quadrupole and non-quadrupole components have implications for the contributions to v 2. They suggest that the main source of the difference between v 2{2} and v 2{4} (or v 2{2D}) is measured properties of minijets.
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License ( https://creativecommons.org/licenses/by-nc/2.0 ), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Kettler, D. Universal centrality and collision energy trends for v 2 measurements from 2D angular correlations. Eur. Phys. J. C 62, 175–181 (2009). https://doi.org/10.1140/epjc/s10052-009-1003-5
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DOI: https://doi.org/10.1140/epjc/s10052-009-1003-5