Pseudorapidity dependence of anisotropic flow and its decorrelations using long-range multiparticle correlations in Pb-Pb and Xe-Xe collisions

Abstract

The pseudorapidity dependence of elliptic ($v_2$), triangular ($v_3$), and quadrangular ($v_4$) flow coefficients of charged particles measured in Pb-Pb collisions at a centre-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and in Xe-Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV with ALICE at the LHC are presented. The measurements are performed in the pseudorapidity range $-3.5<\eta <5$ for various centrality intervals using two- and multi-particle cumulants with the subevent method. The flow probability density function (p.d.f.) is studied with the ratio of flow coefficient $v_2$ calculated with four- and two-particle cumulant, and suggests that the variance of flow p.d.f. is independent of pseudorapidity. The decorrelation of the flow vector in the longitudinal direction is probed using two-particle correlations. The results measured with respect to different reference regions in pseudorapidity exhibit differences, argued to be a result of saturating decorrelation effect above a certain pseudorapidity separation, in contrast to previous publications which assign this observation to non-flow effects. The results are compared to $3+1$ dimensional hydrodynamic and the AMPT transport model calculations. Neither of the models is able to simultaneously describe the pseudorapidity dependence of measurements of anisotropic flow and its fluctuations. The results presented in this work highlight shortcomings in our current understanding of initial conditions and subsequent system expansion in the longitudinal direction. Therefore, they provide input for its improvement.

29 pages, 10 captioned figures, authors from page 23, published version, figures at http://alice-publications.web.cern.ch/node/9495

References in corpus (13)

• Viscosity in Strongly Interacting Quantum Field Theories from Black Hole Physics
• Translation of collision geometry fluctuations into momentum anisotropies in relativistic heavy-ion collisions
• Elliptic flow in the Gaussian model of eccentricity fluctuations
• Event-by-event hydrodynamics and elliptic flow from fluctuating initial state
• The ALICE experiment: a journey through QCD
• Breaking of factorization of two-particle correlations in hydrodynamics
• Forward-backward eccentricity and participant-plane angle fluctuations and their influences on longitudinal dynamics of collective flow
• Influence of temperature dependent shear viscosity on elliptic flow at back- and forward rapidities in ultrarelativistic heavy-ion collisions
• Importance of non-flow in mixed-harmonic multi-particle correlations in small collision systems
• Eccentricity distributions in nucleus-nucleus collisions
• Longitudinal flow decorrelations in Xe+Xe collisions at $\sqrt{s_{\mathrm{NN}}}=5.44$ TeV with the ATLAS detector
• Rapidity decorrelation of anisotropic flow caused by hydrodynamic fluctuations
• Searches for transverse momentum dependent flow vector fluctuations in Pb-Pb and p-Pb collisions at the LHC

Cited by in corpus (2)

• Exploring nuclear structure with multiparticle azimuthal correlations at the LHC
• Systematic study of flow vector fluctuations in $\sqrt{{\text{s}}_{{}_{\mathbf{NN}}}}=5.02$ TeV Pb-Pb collisions