Abstract
Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 . This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients denoting the magnitude of the anisotropy. Significant – values are obtained as a function of transverse momentum ( GeV), pseudorapidity (), and centrality using an event plane method. The values for are found to vary weakly with both and centrality, and their dependencies are found to follow an approximate scaling relation, , except in the top 5 most central collisions. A Fourier analysis of the charged particle pair distribution in relative azimuthal angle () is performed to extract the coefficients . For pairs of charged particles with a large pseudorapidity gap () and one particle with GeV, the – values are found to factorize as in central and midcentral events. Such factorization suggests that these values of – are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the data are consistent with the combined contributions from a rapidity-even and global momentum conservation. A two-component fit is used to extract the contribution. The extracted is observed to cross zero at GeV, reaches a maximum at 4–5 GeV with a value comparable to that for , and decreases at higher .
29 More- Received 14 March 2012
DOI:https://doi.org/10.1103/PhysRevC.86.014907
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©2012 CERN, for the ATLAS Collaboration