Observation of direct-photon collective flow in Au+Au collisions at √S<inf>NN</inf> = 200 GeV

PHENIX Collaboration

Research output: Contribution to journalArticle

152 Citations (Scopus)

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<inf>NN</inf> = 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 v<inf>2</inf> comparable to that of hadrons, whereas model calculations for thermal photons in this kinematic region significantly underpredict the observed v<inf>2</inf>.

Original languageEnglish
Article number122302
JournalPhysical Review Letters
Volume109
Issue number12
DOIs
Publication statusPublished - 2012 Sep 19

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collisions
photons
hadrons
anisotropy
transverse momentum
partons
heavy ions
kinematics
energy dissipation
momentum
detectors
scattering

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Observation of direct-photon collective flow in Au+Au collisions at √S<inf>NN</inf> = 200 GeV. / PHENIX Collaboration.

In: Physical Review Letters, Vol. 109, No. 12, 122302, 19.09.2012.

Research output: Contribution to journalArticle

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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 T. Chujo and P. Chung and O. Chvala and Byungsik Hong and Park, {Sung Keun}",
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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 - Chujo, T.

AU - Chung, P.

AU - Chvala, O.

AU - Hong, Byungsik

AU - Park, Sung Keun

PY - 2012/9/19

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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.

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