No abstract

Measurements of the azimuthal anisotropy in lead–lead collisions at = 5.02 TeV are presented using a data sample corresponding to 0.49 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, – , 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 over wide ranges of the transverse momentum, 0.5 60 GeV, the pseudorapidity, 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 = 2.76 and 5.02 . In particular, the shape of the dependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the and values by constant factors over the centrality interval 0–60% and the range 0.5 5 GeV.

This paper describes the measurements of flow harmonics v 2-v 6 in 3 μb −1 of Xe + Xe collisions at √ s NN = 5.44 TeV performed using the ATLAS detector at the Large Hadron Collider (LHC). Measurements of the centrality, multiplicity, and p 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 nonflow correlations in small collision systems. This nonflow removal is shown to have a significant influence on the measured v n at high p T , especially in peripheral events. Comparisons of the measured v n with measurements in Pb + Pb collisions and p + Pb collisions at √ s 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, N part , 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 N part or multiplicity, but the other harmonics are significantly different. The ratios of the measured v n in Xe + Xe and Pb + Pb collisions, as a function of centrality, are also compared to theoretical calculations.

No abstract

No abstract