@article{5ce11617182742ad862be03e6d60aec2,
title = "Observation of direct-photon collective flow in Au+Au collisions at √SNN = 200 GeV",
abstract = "The second Fourier component v2 of the azimuthal anisotropy with respect to the reaction plane was measured for direct photons at midrapidity and transverse momentum (pT) of 1-13 GeV/c in Au+Au collisions at √SNN = 200 GeV. Previous measurements of this quantity for hadrons with pT < 6 GeV/c indicate that the medium behaves like a nearly perfect fluid, while for pT > 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 pT > 4 GeV/c the anisotropy for direct photons is consistent with zero, as expected if the dominant source of direct photons is initial hard scattering. However, in the pT < 4 GeV/c region dominated by thermal photons, we find a substantial direct photon v2 comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region significantly underpredict the observed v2.",
author = "{PHENIX Collaboration} and A. Adare and S. Afanasiev and C. Aidala and Ajitanand, {N. N.} and Y. Akiba and H. Al-Bataineh and J. Alexander and K. Aoki and Y. Aramaki and Atomssa, {E. T.} and R. Averbeck and Awes, {T. C.} and B. Azmoun and V. Babintsev and M. Bai and G. Baksay and L. Baksay and Barish, {K. N.} and B. Bassalleck and Basye, {A. T.} and S. Bathe and V. Baublis and C. Baumann and A. Bazilevsky and S. Belikov and R. Belmont and R. Bennett and A. Berdnikov and Y. Berdnikov and Bickley, {A. A.} and Bok, {J. S.} and K. Boyle and Brooks, {M. L.} and H. Buesching and V. Bumazhnov and G. Bunce and S. Butsyk and Camacho, {C. M.} and S. Campbell and Chen, {C. H.} and Chi, {C. Y.} and M. Chiu and Choi, {I. J.} and Choudhury, {R. K.} and P. Christiansen and V. Cianciolo and I. Garishvili and Lajoie, {J. G.} and J. Newby and Read, {K. F.}",
year = "2012",
month = sep,
day = "19",
doi = "10.1103/PhysRevLett.109.122302",
language = "English",
volume = "109",
journal = "Physical Review Letters",
issn = "0031-9007",
publisher = "American Physical Society",
number = "12",
}