Investigation Of Anisotropic Flow In Relativistic Heavy-ion Collisions

Quantum-Chromo-Dynamics(QCD)is the fundamental theory that describes hadron-hadron collision on the fm scale.According to QCD,quarks and gluons(partons)are the basic building blocks of the hadrons,and gluons are the carriers of strong interaction.Lattice QCD calculation predicts that matter at extremely high temperature,low baryon density where partons are“deconfined",i.e.not confined together by the QCD force,will create hot and dense matter which is called Quark-Gluon-Plasma(QGP).Such a state of matter was realized in the early universe,a few ?s after the "Big Bang".The Relativistic Heavy Ion Collider at the Brookhaven National Laboratory and the Large Hadron Collider at the European Organization for Nuclear Research produce such a dense,high-temperature matter by accelerating heavy-ions.Anisotropic flow has been widely studied as an important probe for the investiga-tions of QGP signal in relativistic heavy-ion collisions.Event-by-event measurement of anisotropic flow is crucial to understand the initial state conditions and particle produc-tion in heavy-ion collisions.Uranium nuclei provide a unique opportunity to study this,owing to the intrinsic prolate shape and the presence of different overlap configurations in the central collisions like body-body and tip-tip.The measured flow vector distribu-tions are unfolded by a data-driven Bayesian Unfolding process to suppress non-flow and statistic fluctuation to obtain the true flow distributions.To investigate the flow fluc-tuation,multi-particle cumulants are analytically calculated.The ratio of v2{6}/v2{4}is less than unit,which indicates the flow fluctuation is a non-Gaussian fluctuation.Measurement of the flow decorrelation in the longitudinal direction explores the non-boost-invariant nature of the initial collision geometry and final state collective dy-namics.The decorrelations were first observed at the LHC,but are predicted by several(3+1)D hydrodynamic models to be stronger for lower ?SNN at RHIC due to the smaller number of initial partons and shorter string length at lower?SNN.We first measure the flow decorrelation at the RHIC energies.The results show a larger decorrelation effect at RHIC than LHC.Hydrodynamic models tuned to the Pb+Pb data at 2.76 TeV fail to describe the strength of the decorrelation at 54 and 200 GeV.These results will help to constrain the initial condition along longitudinal direction and help to understand the longitudinal evolution of the fireball.The observation of "ridge" in the small systems opens up opportunities to study the collective behaviour.Is the effect a response to initial geometry or initial momentum correlation from gluon saturation effect?The controversy still remains.A new subevent cumulant method was recently developed,which can significantly reduce the non-flow contributions in long-range correlations for small systems.In this work,we use both standard and subevent cumulant methods to study multi-particle correlations in p+Pb collisions at?SNN = 5.02 TeV with a multiphase transport(AMPT)model,including two-and four-particle cumulants(c2{2} and c2{4})and symmetric cumulants(SC(2,3)and SC(2,4)).Our numerical results show that the measurements from the standard cumulant method could be contaminated by some non-flow effects,especially when the number of produced particles is small,hence one better to use the subevent cumulant method to explore the real collectivity in small systems.The elliptic anisotropy and triangular anisotropy of reconstructed jets are investi-gated in Pb+Pb collisions at?SNN= 2.76 TeV within a multiphase transport model.We do observe that the jet energy loss fraction is dependent of the azimuthal angle with re-spect to the different orders of event plane.Azimuthal anisotropies of the reconstructed jet can be utilized as a good probe to study the initial spatial geometry,and imposes constraints on the path-length dependence of jet quenching models.