The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at root s(NN) p 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.

Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV / B., A., B., A., J., A., D., A., A. M., A., M. M., A., G. A., R., M., A., A. G., A., A., A., Z., A., N., A., A. A., M., I., A., S. A., A., S. U., A., I., A., M., A., A., A., D., A., et al.. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - STAMPA. - 111:23(2013), p. 232302. [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

L. Cunqueiro;MEDDI, Franco;
2013

Abstract

The directed flow of charged particles at midrapidity is measured in Pb-Pb collisions at root s(NN) p 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.
2013
Relativistic heavy-ion collisions, Particle and resonance production, Quark deconfinement, quark-gluon plasma production, and phase transitions
01 Pubblicazione su rivista::01a Articolo in rivista
Directed Flow of Charged Particles at Midrapidity Relative to the Spectator Plane in Pb-Pb Collisions at root s(NN)=2.76TeV / B., A., B., A., J., A., D., A., A. M., A., M. M., A., G. A., R., M., A., A. G., A., A., A., Z., A., N., A., A. A., M., I., A., S. A., A., S. U., A., I., A., M., A., A., A., D., A., et al.. - In: PHYSICAL REVIEW LETTERS. - ISSN 0031-9007. - STAMPA. - 111:23(2013), p. 232302. [10.1103/physrevlett.111.232302]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/552529
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