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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
  • Andrew Adare, University of Colorado, Boulder
  • John C. Hill, Iowa State University
  • Todd Kempel, Iowa State University
  • John G. Lajoie, Iowa State University
  • Alexandre Lebedev, Iowa State University
  • Craig Ogilvie, Iowa State University
  • H. Pei, Iowa State University
  • Marzia Rosati, Iowa State University
  • Alexey Yu. Semenov, Iowa State University
  • Carla Vale, Iowa State University
  • Feng Wei, Iowa State University
  • et al.
  • PHENIX Collaboration, PHENIX Collaboration
Document Type
Article
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).
Comments

This is an article from Physical Review Letters 109 (2012):122302-1, doi:10.1103/PhysRevLett.109.122302. Posted with permission.

Copyright Owner
American Physical Society
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/