Hydrodynamic Flow in PbPb Collisions Observed via Azimuthal Angle Correlations of Charged Hadrons

TL;DR

This paper reports measurements of azimuthal angle correlations of charged hadrons in lead-lead collisions at 2.76 TeV, revealing anisotropies linked to the reaction plane and analyzing their dependence on various kinematic variables.

Contribution

It introduces a comprehensive analysis of azimuthal anisotropies using multiple methods to distinguish collective flow from non-flow effects in heavy-ion collisions.

Findings

Measured second Fourier coefficient as a function of pT, η, and centrality.

Extracted higher-order Fourier components at midrapidity.

Compared different analysis methods for sensitivity to non-flow correlations.

Abstract

Azimuthal angle correlations of charged hadrons were measured in $\sqrt s_{NN}$ = 2.76 TeV PbPb collisions by the CMS experiment. The distributions exhibit anisotropies that are correlated with the event-by-event orientation of the reaction plane. Several methods were employed to extract the strength of the signal: the event-plane, cumulant and Lee-Yang Zeros methods. These methods have different sensitivity to correlations that are not caused by the collective motion in the system (non-flow correlations due to jets, resonance decays, and quantum correlations). The second Fourier coefficient of the charged hadron azimuthal distributions was measured as a function of transverse momentum, pseudorapidity and centrality in a broad kinematic range: $0.3 < p_T < 12.0$ GeV/c, $|\eta| < 2.4$, as a function of collision centrality. In addition, the third through sixth Fourier components were measured at midrapidity using selected methods.