Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV

B. Abelev; J. Adam; D. Adamova; A.M. Adare; M.M. Aggarwal; Ian Bearden; Hans Bøggild; Christian Holm Christensen; Ante Bilandzic; Hans Hjersing Dalsgaard; Jens Jørgen Gaardhøje; Kristjan Herlache Gulbrandsen; Alexander Colliander Hansen; Børge Svane Nielsen; Casper Nygaard; Carsten Søgaard

doi:10.1103/PhysRevLett.111.232302

Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV

B. Abelev, J. Adam, D. Adamova, A.M. Adare, M.M. Aggarwal, Ian Bearden, Hans Bøggild, Christian Holm Christensen, Ante Bilandzic, Hans Hjersing Dalsgaard, Jens Jørgen Gaardhøje, Kristjan Herlache Gulbrandsen, Alexander Colliander Hansen, Børge Svane Nielsen, Casper Nygaard, Carsten Søgaard

Experimental Particle Physics

47 Citations (Scopus)

Abstract

The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at √s_NN=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta p_T between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even p_T shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.

Original language	English
Article number	232302
Journal	Physical Review Letters
Volume	111
Issue number	23
ISSN	0031-9007
DOIs	https://doi.org/10.1103/PhysRevLett.111.232302
Publication status	Published - 6 Dec 2013

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Abelev, B., Adam, J., Adamova, D., Adare, A. M., Aggarwal, M. M., Bearden, I., Bøggild, H., Christensen, C. H., Bilandzic, A., Dalsgaard, H. H., Gaardhøje, J. J., Gulbrandsen, K. H., Hansen, A. C., Nielsen, B. S., Nygaard, C., & Søgaard, C. (2013). Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV. Physical Review Letters, 111(23), [232302]. https://doi.org/10.1103/PhysRevLett.111.232302

Abelev, B, Adam, J, Adamova, D, Adare, AM, Aggarwal, MM, Bearden, I , Bøggild, H , Christensen, CH, Bilandzic, A, Dalsgaard, HH, Gaardhøje, JJ , Gulbrandsen, KH, Hansen, AC, Nielsen, BS, Nygaard, C & Søgaard, C 2013, 'Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV', Physical Review Letters, vol. 111, no. 23, 232302. https://doi.org/10.1103/PhysRevLett.111.232302

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title = "Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV",

abstract = "The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at √sNN=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta pT between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even pT shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.",

author = "B. Abelev and J. Adam and D. Adamova and A.M. Adare and M.M. Aggarwal and Ian Bearden and Hans B{\o}ggild and Christensen, {Christian Holm} and Ante Bilandzic and Dalsgaard, {Hans Hjersing} and Gaardh{\o}je, {Jens J{\o}rgen} and Gulbrandsen, {Kristjan Herlache} and Hansen, {Alexander Colliander} and Nielsen, {B{\o}rge Svane} and Casper Nygaard and Carsten S{\o}gaard",

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doi = "10.1103/PhysRevLett.111.232302",

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T1 - Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV

AU - Abelev, B.

AU - Adam, J.

AU - Adamova, D.

AU - Adare, A.M.

AU - Aggarwal, M.M.

AU - Bearden, Ian

AU - Bøggild, Hans

AU - Christensen, Christian Holm

AU - Bilandzic, Ante

AU - Dalsgaard, Hans Hjersing

AU - Gaardhøje, Jens Jørgen

AU - Gulbrandsen, Kristjan Herlache

AU - Hansen, Alexander Colliander

AU - Nielsen, Børge Svane

AU - Nygaard, Casper

AU - Søgaard, Carsten

PY - 2013/12/6

Y1 - 2013/12/6

N2 - The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at √sNN=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta pT between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even pT shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.

AB - The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at √sNN=2.76 TeV relative to the collision symmetry plane defined by the spectator nucleons. A negative slope of the rapidity-odd directed flow component with approximately 3 times smaller magnitude than found at the highest RHIC energy is observed. This suggests a smaller longitudinal tilt of the initial system and disfavors the strong fireball rotation predicted for the LHC energies. The rapidity-even directed flow component is measured for the first time with spectators and found to be independent of pseudorapidity with a sign change at transverse momenta pT between 1.2 and 1.7 GeV/c. Combined with the observation of a vanishing rapidity-even pT shift along the spectator deflection this is strong evidence for dipolelike initial density fluctuations in the overlap zone of the nuclei. Similar trends in the rapidity-even directed flow and the estimate from two-particle correlations at midrapidity, which is larger by about a factor of 40, indicate a weak correlation between fluctuating participant and spectator symmetry planes. These observations open new possibilities for investigation of the initial conditions in heavy-ion collisions with spectator nucleons.

U2 - 10.1103/PhysRevLett.111.232302

DO - 10.1103/PhysRevLett.111.232302

M3 - Journal article

C2 - 24476260

SN - 0031-9007

VL - 111

JO - Physical Review Letters

JF - Physical Review Letters

IS - 23

M1 - 232302

ER -

Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV

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