Hydrodynamic flow in PbPb collisions observed via azimuthal angle correlations of charged hadrons

Eric Appelt,Cms Collaboration

doi:10.1063/1.3700679

Abstract

Azimuthal angle correlations of charged hadrons were measured in sNN = 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 < pT < 12.0 GeV/c, |η| < 2.4, as a function of collision centrality. In addition, the third through sixth Fourier components were measured at midrapidity using selected methods.

Highlights

In non-central heavy ion collisions, the initial spatial asymmetry of the collision zone leads to anisotropies in the final state charged hadron emission
The elliptic flow (v2) analysis [4] was performed with the event plane method [5], 2 and 4-particle cumulant method [6, 7], and the Lee-Yang zeros (LYZ) method [8, 9]
This provides a gap of 1 < ∆η < 3.4 between the tracks used in the elliptic flow measurement and those used in the event plane determination, which is expected to reduce the effect of non-flow correlations on the measurement

Summary

Introduction

In non-central heavy ion collisions, the initial spatial asymmetry of the collision zone leads to anisotropies in the final state charged hadron emission. The strength of this flow is measured through a Fourier expansion of the charged hadron azimuthal distributions with respect to the reaction plane, defined by the impact parameter vector and collision direction. Extracting the transport coefficients of the strongly coupled quark-gluon plasma from measured flow is difficult as the initial state can only be described by theoretical modeling.

Results

Conclusion