Measurement of $v_{n}$ coefficients and event plane correlations in 2.76 TeV Pb-Pb collisions with ATLAS

TL;DR

This paper reports detailed measurements of flow harmonics and event plane correlations in Pb-Pb collisions at 2.76 TeV, revealing insights into initial geometry and medium expansion in heavy ion collisions.

Contribution

It provides the first comprehensive measurement of $v_n$ coefficients up to $n=6$ and their correlations, including the extraction of dipolar $v_1$ considering momentum conservation effects.

Findings

Factorization of two-particle correlations for $n=2-6$

Global momentum conservation affects $v_1$ measurements

Dipolar $v_1$ magnitude is comparable to $v_3$

Abstract

Measurements of flow harmonics $v_1-v_6$ are presented in a broad range of transverse momentum and centrality for $\sqrt{s_{NN}} = 2.76$ TeV Pb-Pb collisions with the ATLAS experiment. The fourier coefficients of two-particle correlations are shown to factorize as products of the single particle $v_n$ for $n=2-6$. The factorization breaks for $n=1$ due to effects of global momentum conservation. The dipolar $v_1$ associated with the initial dipole asymmetry is extracted from the two-particle correlations via a two component fit that accounts for momentum conservation. The magnitude of the extracted dioplar $v_1$ is comparable to $v_3$. Measurements of correlations between harmonic planes of different orders, which give additional constraints on the initial geometry and expansion mechanism of the medium produced in the heavy ion collisions, are also presented.