Measurements of Anisotropic Flow in Xe–Xe Collisions at √sNN = 5.44 TeV Using the ALICE Detector

Jonatan Adolfsson

doi:10.3390/proceedings2019010041

Abstract

These proceedings summarise the first measurements of anisotropic flow coefficients v n , 2 ≤ n ≤ 4 , for inclusive charged particles at mid-rapidity in Xe–Xe collisions at s NN = 5 . 44 TeV . The results are compared with those from Pb–Pb collisions at s NN = 5 . 02 TeV , in order to test the initial state (IS) models and transport properties. The resulting differences in v 2 and v 3 between the two systems are consistent with two different hydrodynamical models. Moreover, it is expected that the ratios between v n and their corresponding eccentricities for n = 2 , 3 scale with transverse density. This is observed for some IS models, except for some deviations in central collisions. These results assist in constraining the initial state as well as the hydrodynamical propagation of the system.

Highlights

These proceedings mainly summarise the contents of Ref. [1]
For an anisotropic initial state—which can be due to either an off-centre impact, or to fluctuations affecting the shape—the final state will be anisotropic, resulting in an anisotropic momentum distribution of the resulting particles. This is known as anisotropic flow, which is characterised by the flow coefficients vn, obtained from the
MC KLN [12]. (Top right) TR ENTo [7]. (Bottom) MC Glauber using 3, 5, and 7 constituent quarks as sources [11], respectively. The fact that both the hydrodynamic prediction of v2 {4}/v2 {2, |∆η > 2|} and the corresponding eccentricity ratio agree reasonably well with the data in Figure 1a indicates that Equation (2) holds approximately and that flow fluctuations are preserved in the hydrodynamic expansion

Summary

Introduction

These proceedings mainly summarise the contents of Ref. [1]. In relativistic heavy-ion collisions, it is believed that a quark-gluon plasma (QGP) is formed, which is a hot and dense state of matter, behaving as a nearly perfect fluid. For an anisotropic initial state—which can be due to either an off-centre impact, or to fluctuations affecting the shape—the final state will be anisotropic, resulting in an anisotropic momentum distribution of the resulting particles This is known as anisotropic flow, which is characterised by the flow coefficients vn , obtained from the Fourier expansion ∞ dN. Dφ n=1 where φ is the azimuthal angle, n is the flow harmonic, and Ψn is the associated symmetry plane angle This observable is sensitive to the initial state (IS) model used, and to a lesser extent to the shear viscosity over entropy ratio (η/s) of the medium. To constrain these models and parameters, it is useful to make measurements across various collision systems of different sizes. It is assumed that the relation [2]

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Conclusion