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Eur. Phys. J. C 62, 175-181 (2009)
DOI: 10.1140/epjc/s10052-009-1003-5
Universal centrality and collision energy trends for v 2 measurements from 2D angular correlations
David KettlerUniversity of Washington, Washington, USA
dkettler@u.washington.edu
Received 1 October 2008 / Revised version 9 March 2009 / Published online 15 April 2009
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) 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
). 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) is measured properties of minijets.
© Società Italiana di Fisica, Springer-Verlag 2009
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