Anisotropic Flow And Flow Fluctuations Of Identified Hadrons In Pb-Pb Collisions With The ALICE Detector

The quark-gluon plasma(QGP),a new state of nuclear matter that is believed to have existed in the early universe,can be created in high-energy heavy-ion collisions.The study of it has a profound impact on understanding the evolution of the universe,the formation of stars,the elementary constitutes and the interaction of matter,and many other aspects.Because of QGP's extremely short survival time and high temperature,it is almost impossible to be observed directly.Fortunately,a large amount of final state information can be extracted in relativistic heavy-ion collisions to probe its formation and investigate its properties.Anisotropic flow is such an effective characteristic signal of QGP.Measurements of the anisotropy flow coefficients vn of inclusive charged particles point out that the QGP behaves similarly to an almost perfect liquid.In the typical non-central heavy-ion collisions,the initial geometry spatial anisotropy of the almond-like overlap region would be transferred into the final state momentum anisotropy by the interactions among constituents.Besides,the fluctuations of nucleon distribution would lead to the final state flow fluctuations.Measurements of the flow and flow fluctuations can provide strict constraints for the theory calculations describing the medium evolution and initial conditions of the evolving system created in heavy-ion collisions.The analysis of these two observables of identified particles can help us further explore the initial conditions,evolution process,and particle generation mechanism and probe the freezing conditions of the system.This work presents the measurements of anisotropic flow and flow fluctuations of identi-fied particles,including especially multi-strange baryons in Pb-Pb collisions at(?)=5.02 TeV with the ALICE(A Large Ion Collision Experiment)detector at the LHC(Large Hadron Collider).Multi-strange particles are expected to have small hadronic cross-sections and are less affected by hadronic rescattering.Therefore,the anisotropic flow of multi-strange particles is expected to be particularly sensitive to the dynamics of the partonic stage of heavy-ion collisions.Firstly,their elliptic flow coefficient v2 and triangular flow coefficient v3 were measured by three sub-events scalar product method.The measurements show that the v2 and v3 of multi-strange particles ?-+?+and ?-+?+respect the mass ordering at low transverse momentum(pT<3)GeV/c.It means that the heavier particles have smaller v2 than lighter particles at the same pT.The v2 and v3 of them tend to have similar behaviours to that of baryons p+p and ?+? at intermediate pT(3<pT<10 GeV/c).In addition,the elliptic flow coefficient v2 of identified particles ?±,K±,p+p,?,KS0,?+?,?-+?+and ?-+?+were measured by 2-and 4-particle cumulant approaches.Different from the scalar product method,in the 2-and 4-particle cumulant measurements only the center detector with more accurate azimuth angle determination capability is utilized to reconstructed the final state particles.Besides,the 4-particle cumulant is less affected by the non-flow effect.Therefore,these two measurements would give more accurate v2.The results of identified par-ticles from multi-particle correlations also show mass ordering for v2 at lower pT region,baryon and meson grouping at intermediate pT.Finally,the elliptic flow v2{2} measured by the 2-particle cumulant method and v2{4} by the 4-particle cumulant method are affected differently by flow fluctuations.If the probability density function of v2 follows the Bessel-Gaussian distribution,then the flow fluctuations can be quantified by the second moment of the probability distribution.Therefore,the characteristics of flow fluctuations are studied by measuring the ratio of v2{4} to v2{2} and the ratio of the second moment to the first moment of the probability distribution,F(v2).If there is no obvious particle species dependence,the flow fluctuations would mainly come from the initial state geometry fluctuations.However,a non-trivial particle species dependence of v2{4}/v2{2} and F(v2)is observed at 1<pT<3 GeV/c in 40-50%and 50-60%centrality classes of Pb-Pb collisions,indicating that the flow fluctuations are not only purely due to the initial state geometry fluctuations.In the end,the measurements are compared with hydrodynamic model calculations.The comparison shows that the measurements could constrain the initial conditions of the hydrodynamic model.