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Article
Observation of Direct-Photon Collective Flow in Au plus Au Collisions at root s(NN)=200 GeV
Physical Review Letters
Document Type
Article
Disciplines
Publication Version
Published Version
Publication Date
9-19-2012
DOI
10.1103/PhysRevLett.109.122302
Abstract
The second Fourier component v(2) of the azimuthal anisotropy with respect to the reaction plane is measured for direct photons at midrapidity and transverse momentum (p(T)) of 1-12 GeV/c in Au + Au collisions at root s(NN) = 200 GeV. Previous measurements of this quantity for hadrons with p(T) < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for p(T) > 6 GeV/c a reduced anisotropy is interpreted in terms of a path-length dependence for parton energy loss. In this measurement with the PHENIX detector at the Relativistic Heavy Ion Collider we find that for p(T) > 4 GeV/c the anisotropy for direct photons is consistent with zero, which is as expected if the dominant source of direct photons is initial hard scattering. However, in the p(T) < 4 GeV/c region dominated by thermal photons, we find a substantial direct-photon v(2) comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region underpredict the observed v(2).
Copyright Owner
American Physical Society
Copyright Date
2012
Language
en
File Format
application/pdf
Citation Information
Andrew Adare, John C. Hill, Todd Kempel, John G. Lajoie, et al.. "Observation of Direct-Photon Collective Flow in Au plus Au Collisions at root s(NN)=200 GeV" Physical Review Letters Vol. 109 Iss. 12 (2012) p. 122302 Available at: http://works.bepress.com/craig-ogilvie/86/
This is an article from Physical Review Letters 109 (2012):122302-1, doi:10.1103/PhysRevLett.109.122302. Posted with permission.