Observation of direct-photon collective flow in Au+Au collisions at √SNN = 200 GeV

PHENIX Collaboration

doi:10.1103/PhysRevLett.109.122302

Observation of direct-photon collective flow in Au+Au collisions at √S_NN = 200 GeV

PHENIX Collaboration

University of Colorado Boulder
Joint Institute for Nuclear Research
University of Massachusetts
Stony Brook University
RIKEN
Brookhaven National Lab
New Mexico State University
Kyoto University
The University of Tokyo
Laboratoire Leprince-Ringuet
Oak Ridge National Laboratory
Brookhaven National Laboratory
Institute for High Energy Physics
Florida Institute of Technology
University of California at Riverside
University of New Mexico
Abilene Christian University
Petersburg Nuclear Physics InstituteGatchina
University of Münster
Vanderbilt University
Peter the Great St. Petersburg Polytechnic University
Yonsei University
Los Alamos National Laboratory
Columbia University
Homi Bhabha National Institute

Research output: Contribution to journal › Article › peer-review

213 Scopus citations

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 √S_NN = 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.

Original language	English
Article number	122302
Journal	Physical Review Letters
Volume	109
Issue number	12
DOIs	https://doi.org/10.1103/PhysRevLett.109.122302
State	Published - Sep 19 2012

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10.1103/PhysRevLett.109.122302

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@article{98c1784661d74525a015cfc942a553db,

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 Abhay Deshpande and A. Drees and Hemmick, \{T. K.\} and J. Jia and R. Lacey",

year = "2012",

month = sep,

day = "19",

doi = "10.1103/PhysRevLett.109.122302",

language = "English",

volume = "109",

journal = "Physical Review Letters",

issn = "0031-9007",

number = "12",

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TY - JOUR

T1 - Observation of direct-photon collective flow in Au+Au collisions at √SNN = 200 GeV

AU - PHENIX Collaboration

AU - Adare, A.

AU - Afanasiev, S.

AU - Aidala, C.

AU - Ajitanand, N. N.

AU - Akiba, Y.

AU - Al-Bataineh, H.

AU - Alexander, J.

AU - Aoki, K.

AU - Aramaki, Y.

AU - Atomssa, E. T.

AU - Averbeck, R.

AU - Awes, T. C.

AU - Azmoun, B.

AU - Babintsev, V.

AU - Bai, M.

AU - Baksay, G.

AU - Baksay, L.

AU - Barish, K. N.

AU - Bassalleck, B.

AU - Basye, A. T.

AU - Bathe, S.

AU - Baublis, V.

AU - Baumann, C.

AU - Bazilevsky, A.

AU - Belikov, S.

AU - Belmont, R.

AU - Bennett, R.

AU - Berdnikov, A.

AU - Berdnikov, Y.

AU - Bickley, A. A.

AU - Bok, J. S.

AU - Boyle, K.

AU - Brooks, M. L.

AU - Buesching, H.

AU - Bumazhnov, V.

AU - Bunce, G.

AU - Butsyk, S.

AU - Camacho, C. M.

AU - Campbell, S.

AU - Chen, C. H.

AU - Chi, C. Y.

AU - Chiu, M.

AU - Choi, I. J.

AU - Choudhury, R. K.

AU - Christiansen, P.

AU - Deshpande, Abhay

AU - Drees, A.

AU - Hemmick, T. K.

AU - Jia, J.

AU - Lacey, R.

PY - 2012/9/19

Y1 - 2012/9/19

N2 - 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.

AB - 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.

UR - https://www.scopus.com/pages/publications/84866527479

U2 - 10.1103/PhysRevLett.109.122302

DO - 10.1103/PhysRevLett.109.122302

M3 - Article

AN - SCOPUS:84866527479

SN - 0031-9007

VL - 109

JO - Physical Review Letters

JF - Physical Review Letters

IS - 12

M1 - 122302

ER -

Observation of direct-photon collective flow in Au+Au collisions at √S_NN = 200 GeV

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