Longitudinal and azimuthal evolution of two-particle transverse momentum correlations in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 2.76 TeV

Abstract

This paper presents the first measurements of the charge independent (CI) and charge dependent (CD) two-particle transverse momentum correlators $G_2^{\mathrm{CI}}$ and $G_2^{\mathrm{CD}}$ in Pb--Pb collisions at $\sqrt{s_{\text{NN}}} = 2.76\;\text{\TeVe}$ by the ALICE collaboration. The two-particle transverse momentum correlator $G_2$ was introduced as a measure of the momentum current transfer between neighbouring system cells. The correlators are measured as a function of pair separation in pseudorapidity ($\Delta \eta$) and azimuth ($\Delta \phi$) and as a function of collision centrality. From peripheral to central collisions, the correlator $G_2^{\mathrm{CI}}$ exhibits a longitudinal broadening while undergoing a monotonic azimuthal narrowing. By contrast, $G_2^{\mathrm{CD}}$ exhibits a narrowing along both dimensions. These features are not reproduced by models such as HIJING and AMPT. However, the observed narrowing of the correlators from peripheral to central collisions is expected to result from the stronger transverse flow profiles produced in more central collisions and the longitudinal broadening is predicted to be sensitive to momentum currents and the shear viscosity per unit of entropy density $\eta /s$ of the matter produced in the collisions. The observed broadening is found to be consistent with the hypothesized lower bound of $\eta /s$ and is in qualitative agreement with values obtained from anisotropic flow measurements.

20 pages, 5 captioned figures, authors from page 15, published version, figures at http://alice-publications.web.cern.ch/node/5643

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Cited by in corpus (8)

• The ALICE experiment: a journey through QCD
• Extraction of the specific shear viscosity of quark-gluon plasma from two-particle transverse momentum correlations
• A model investigation of the longitudinal broadening of the transverse momentum two-particle correlator
• System size and energy dependence of the mean transverse momentum fluctuations at the LHC
• Two-particle transverse momentum correlations in pp and p-Pb collisions at energies available at the CERN Large Hadron Collider
• Azimuthal dependence of two-particle transverse momentum current correlations
• Measurements of differential two-particle number and transverse momentum correlation functions in pp collisions at $\sqrt{\text{s}}$ = 13 TeV
• Investigating $\Lambda$ baryon production in p-Pb collisions in jets and the underlying event using angular correlations