Measurement of the azimuthal anisotropy of charged particles produced in $\sqrt{s_\mathrm{NN}} = 5.02$ TeV Pb+Pb collisions with the ATLAS detector

TL;DR

This paper reports detailed measurements of azimuthal anisotropy (flow harmonics) of charged particles in Pb+Pb collisions at 5.02 TeV using the ATLAS detector, exploring flow behavior across various collision centralities and transverse momenta.

Contribution

It provides comprehensive flow harmonic measurements over wide kinematic ranges and compares different analysis methods at 5.02 TeV, extending previous results at lower energies.

Findings

Flow harmonics shape is similar across centralities after scaling.

Flow coefficients are measured up to $v_7$.

Results are consistent with previous measurements at different energies.

Abstract

Measurements of the azimuthal anisotropy in lead-lead collisions at $\sqrt{s_\mathrm{NN}} = 5.02$ TeV are presented using a data sample corresponding to 0.49 $\mathrm{nb}^{-1}$ integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for "ultra-central" collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, $v_{2}-v_{7}$, which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics $v_{n}$ over wide ranges of the transverse momentum, 0.5 $<p_{\mathrm{T}}<$ 60 GeV, the pseudorapidity, $|\eta|<$ 2.5, and the collision centrality $0-80$%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at $\sqrt{s_\mathrm{NN}} = 2.76$ TeV and 5.02 TeV. In particular, the shape of the $p_{\mathrm{T}}$ dependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the $v_{n}$ and $p_{\mathrm{T}}$ values by constant factors over the centrality interval $0-60$% and the $p_{\mathrm{T}}$ range $0.5 < p_{\mathrm{T}} < 5$ GeV.