Measurement of the azimuthal anisotropy of charged-particle production in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV with the ATLAS detector

TL;DR

This study measures flow harmonics in Xe+Xe collisions at 5.44 TeV using the ATLAS detector, revealing how azimuthal anisotropy varies with centrality, multiplicity, and collision system, and comparing results with Pb+Pb and p+Pb collisions.

Contribution

It introduces a new template-fit method to remove non-flow effects in small collision systems and provides detailed measurements of flow harmonics in Xe+Xe collisions at the LHC.

Findings

Xe+Xe flow harmonics are larger than Pb+Pb in central collisions.

Flow harmonics decrease with decreasing centrality or increasing harmonic order.

Similar $v_3$ values in Xe+Xe and Pb+Pb at the same participant number or multiplicity.

Abstract

This paper describes the measurements of flow harmonics $v_2$-$v_6$ in 3 $\mu\mathrm{b}^{-1}$ of Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV performed using the ATLAS detector at the LHC. Measurements of the centrality, multiplicity and $p_{\mathrm{T}}$ dependence of the $v_n$ obtained using two-particle correlations and the scalar product technique are presented. The measurements are also performed using a template-fit procedure, which was developed to remove non-flow correlations in small collision systems. This non-flow removal is shown to have a significant influence on the measured $v_n$ at high $p_{\mathrm{T}}$, especially in peripheral events. Comparisons of the measured $v_n$ with measurements in Pb+Pb collisions and $p$+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV are also presented. The $v_n$ values in Xe+Xe collisions are observed to be larger than those in Pb+Pb collisions for $n=2$, 3 and 4 in the most central events. However, with decreasing centrality or increasing harmonic order $n$, the $v_n$ values in Xe+Xe collisions become smaller than those in Pb+Pb collisions. The $v_n$ in Xe+Xe and Pb+Pb collisions are also compared as a function of the mean number of participating nucleons, $\langle N_\text{part} \rangle$, and the measured charged-particle multiplicity in the detector. The $v_3$ values in Xe+Xe and Pb+Pb collisions are observed to be similar at the same $\langle N_\text{part}\rangle$ or multiplicity, but the other harmonics are significantly different. Comparisons of the $v_n$ measurements with theoretical calculations are also made.