Systematic study of flow vector fluctuations in $\sqrt{{\text{s}}_{{}_{\mathbf{NN}}}}=5.02$ TeV Pb-Pb collisions

Abstract

Measurements of the $p_{\mathrm{T}}$-dependent flow vector fluctuations in Pb-Pb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02\mathrm{TeV}$ using azimuthal correlations with the ALICE experiment at the Large Hadron Collider are presented. A four-particle correlation approach [1] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the $p_{\mathrm{T}}$-dependent flow vector fluctuations at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02\mathrm{TeV}$ with two-particle correlations. Significant $p_{\mathrm{T}}$-dependent fluctuations of the ${\vec{V}}_2$ flow vector in Pb-Pb collisions are found across different centrality ranges, with the largest fluctuations of up to $\sim$15% being present in the 5% most central collisions. In parallel, no evidence of significant $p_{\mathrm{T}}$-dependent fluctuations of ${\vec{V}}_3$ or ${\vec{V}}_4$ is found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more than $5\ddot{I}ƒ$ significance in central collisions. These observations in Pb-Pb collisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high $p_{\mathrm{T}}$, which might be biased by $p_{\mathrm{T}}$-dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be re-examined to improve our understanding of initial conditions, quark--gluon plasma properties, and the dynamic evolution of the created system.

29 pages, 9 captioned figures, 1 table, authors from page 23, published version, figures at http://alice-publications.web.cern.ch/node/10850