CERN Accelerating science

ATLAS Slides
Report number	ATL-PHYS-SLIDE-2020-184
Title	ATLAS measurements of transverse and longitudinal flow fluctuations
Author(s)	Behera, Arabinda (Stony Brook University)
Corporate author(s)	The ATLAS collaboration
Collaboration	ATLAS Collaboration
Submitted to	10th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions, Austin (remote Only), Tx, Usa, 31 May - 5 Jun 2020
Submitted by	[email protected] on 09 Jun 2020
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; ATLAS
Free keywords	HEAVYIONS
Abstract	ATLAS measurements of flow harmonics ($v_n$) and their fluctuations in Pb+Pb and Xe+Xe collisions covering a wide range of transverse momenta, pseudorapidity and collision centrality are presented. The measurements are performed using data from Xe+Xe collisions at 5.44 TeV, Pb+Pb collisions at 5.02 TeV, and $p$+Pb collisions at 5.02 and 8.16 TeV. The $v_n$ are measured up to n=6 using the two-particle correlations, multi-particle cumulants, and scalar product methods. The $v_n$ values are also performed using a non-flow subtraction technique that was developed for flow measurements in $pp$ and $p$+Pb collisions. This non-flow subtraction is found to have a significant effect on the measured $v_n$ at high-$p_T$ and in peripheral collisions. A universal scaling in the $p_T$ dependence of the $v_n$ is observed for both systems. Measurements of correlations between the $v_n$ for different order n, studied with three- and four-particle mixed-harmonic cumulants, are also presented, and contributions to these correlations from ``centrality fluctuations'' are also discussed. Measurements of longitudinal flow decorrelations involving two- and four-particle correlations for $v_2$ and $v_3$ in Xe+Xe and $p$+Pb collisions are also presented and compared with the corresponding measurements in Pb+Pb collisions. The four-particle decorrelation is found to not factorize as a product of two-particle decorrelations. The ability of such measurements to distinguish between different models of initial geometry and to reduce the uncertainty in determining the effective shear-viscosity to entropy-density ratio of the QGP is demonstrated.