Study Of Triangular Flow And Flactuating Initial Condition With IEBE-VISHNU Model

The Relativistic Heavy-Ion Collider?RHIC?and the Large Hadron Collider?LHC?provide unique experimental access to a new state of matter at extremely high densities and temperatures: the Quark Gluon Plasma?QGP?,in which quarks and gluons are no longer confined inside individual nucleons.Studying the thermodynamic and transport properties of the QGP will help us understand emergent phenomena in hot and dense manybody systems governed by the strong interaction.However,these 'little bangs' are almost point-like in size(V ? 10^-42m³)and disappear almost instantaneously(? ? 5 × 10^-23s).This makes it impossible to use external probes to measure the properties of the QGP.In order to extract the dynamical evolution of relativistic heavy-ion collisions,one has to rely on realistic theoretical model simulations,which back trace the final experimental observables to the early stage of the collisions.The triangular flow originates from the initial state fluctuation and can reflect the early information of the collision system.Through the study of triangular flow,we can promote the fluctuation nature of collision source and the understanding of QGP evolution Stage.In this paper,a hybrid model iEBE-VISHNU?Event-By Event Viscous Israel Stewart Hydrodynamics and Urqmud?model based on?2+1?dimensional viscous fluid dynamics model simulates the event-by-event relativistic heavy-ion collision process,Pb+Pb collision ats = 2.76 TeV,the initial fluctuation of the system and the triangular flow are obtained.First,the transverse momentum spectrum of the charged particle triangular flow is analyzed and compared with the elliptical flow.Then,the transverse momentum spectra of charged particles in different centrality bins are analyzed.The relation between the centrality and the initial state of the system is studied,and the influence of the centrality on the triangular flow can be reflected by the relationship between the triangle flow and the initial state fluctuation.Then,the relationship between the triangular flow and the thirdorder eccentricity of the centrality is analyzed.The results show that the size of triangular flow is directly related to the fluctuation of initial state.The event-by-event fluctuation of initial conditions produces triangular flow,so the triangular flow itself will have an event-by-case fluctuation.We analyzed the distribution of initial and triangular flows in different centrality bins of charged particles,and try to fit and find the law.Then,the fluctuation of triangular flow is analyzed quantitatively,and the concept of absolute fluctuation and relative fluctuation is introduced.In this paper,the transverse flow fluctuation momentum spectra of charged particles,the fluctuation of triangular flow as the function of the centrality are analyzed,and the fluctuation regularity of the triangle flow under different centrality bins is explored.Triangular flow is sensitive not only to initial conditions,but also to viscosity entropy ratio??/s?in the QGP evolution.Therefore,we analyzed the transverse momentum spectra of charged particles and the function of the integral triangular flow as the viscosity entropy ratio in the case of different viscosity-entropy ratios.The results show that the triangular flow is sensitive to the viscosity-entropy ratio.However,the large fluctuation of the triangular flow may obscure the accuracy of the viscous entropy ratio constrained by triangular flow.Unless the fluctuation is reasonably restricted,the sensitivity of the flow value to the viscosity entropy ratio will be greatly reduced.Therefore,we analyzed the effect of the viscosity-entropy ratio on the triangular flow fluctuation,and find the law to ensure the sensitivity of the triangular flow to the viscosity.