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

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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 √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{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",

}

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 - Cianciolo, V.

AU - Garishvili, I.

AU - Lajoie, J. G.

AU - Newby, J.

AU - Read, K. F.

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 - http://www.scopus.com/inward/record.url?scp=84866527479&partnerID=8YFLogxK

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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