Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb--Pb Collisions at √SNN = 2.76 TeV

Abelev, B. and Planinić, Mirko and Poljak, Nikola and Simatović, Goran and Zyzak, M. (ALICE Collaboration) (2013) Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb--Pb Collisions at √SNN = 2.76 TeV. Physical Review Letters, 111 (23). pp. 232302-11. ISSN 0031-9007

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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.

Item Type: Article
Date: December 2013
Subjects: NATURAL SCIENCES > Physics
Additional Information: Copyright (2013) by the American Physical Society.
Divisions: Faculty of Science > Department of Physics
Project code: 098-0982887-2878, 119-0982887-1006
Publisher: American Physical Society
Depositing User: mag. bibl. Marija Turković
Date Deposited: 15 Sep 2014 12:14
Last Modified: 23 Feb 2016 15:08
URI: http://digre.pmf.unizg.hr/id/eprint/2769

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