https://doi.org/10.1140/epjc/s10052-009-1003-5
Regular Article - Experimental Physics
Universal centrality and collision energy trends for v 2 measurements from 2D angular correlations
University of Washington, Washington, USA
* e-mail: dkettler@u.washington.edu
Received:
1
October
2008
Revised:
9
March
2009
Published online:
15
April
2009
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
). 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.
© Springer-Verlag , 2009
