Study Of Anisotropic Collective Flows And Flow Correlations In Heavy-ion Collisions At The LHC

Since the 2000s,quark-gluon plasma(QGP)has been created in relativistic heavy-ion collisions at the Relativistic Heavy Ion Collider(RHIC)and the Large Hadron Collider(LHC).Due to the strong interaction between the thermalized dense matter,the initial geometric eccentricity of the fireball is transformed into the mo-mentum anisotropy of the final state through viscous fluid dynamics evolution.The anisotropic collective flows can quantify the anisotropy of the momentum distribution of final state particles.The successful description of anisotropic collective flows by fluid dynamics shows that the produced medium behaves as a nearly perfect fluid,and the ratio of shear viscosity to entropy density ?/s is close to the conjected lower limit of 1/4?.Current researches hope to simultaneously constrain the initial eccentricity coef-ficients ?n and the ratio of shear viscosity to entropy density ?/s through a full set of flow coefficients.However,recent studies found that the response of higher-order flow?n(n>3)to the corresponding initial eccentricities ?n is nonlinear due to the mode-coupling effects.Therefore,?/s could not be constrained directly by high-order flow coefficients.In addition to flow coefficients,the study of the flow angle correlations and flow amplitude correlations between the anisotropic flows of different orders can also reveal the early dynamics and transport properties of the generated QGP.At present,the theoretical models have been able to quantitatively describe the experi-mentally measured flow angle correlations.However,the flow amplitude correlations are more affected by the initial conditions and ?/s,so it is a challenge to quantita-tively describe the correlations between the flow coefficients of different orders.The nonlinear coupling coefficients can help us to study the transport properties of QGP.In this thesis,we study the anisotropic flow coefficients in the longitudinal direc-tion of relativistic heavy-ion collisions and flow correlations,using the(3+1)CLVisc-hydro hydrodynamics simulations with fluctuating initial conditions from the AMPT and TRENTo models.We study the pseudo-rapidy dependence of elliptic flow,triangular flow and quadrilateral flow,for PbPb at(?),PbPb at(?)(?)and 00 at(?)with different centrality ranges.It is found that the shape of ?n(?)does not change significantly for different collision centrality bins,and different col-lision systems.This demonstrates that vn(n=2,3)are not Lorentz boost invariant along the longitudinal direction.The dependence of elliptic flow v2 and triangular flow ?3 at midrapidy on the collision centrality and Npart are similar to the eccen-tricity ?n(n=2,3).This indicates that the final elliptical flow ?2 and the triangular flow ?3 are mainly due to the contribution of the space geometry of the produced fireball.In other words,there is a strong linear correlation between the low-order anisotropic flow and the initial eccentricity.We also found that the nonlinear cou-pling coefficients ?422,?523,?633 X6222 can describe the experimental data well with both the AMPT and TRENTo initial conditions of PbPb at(?)and PbPb at(?)By comparing with different collision systems,the nonlinear coupling coefficients are larger for the higher collision energy and larger system size.This can the understood since the hydrodynamic evolution time is longer for the higher collision energy and larger system size.By comparing the calcula-tion with AMPT and TRENTo initial conditions,we found that nonlinear coupling coefficients have little dependence on initial conditions.Therefore,the nonlinear cou-pling coefficients could help constrain the transport coefficients and understand the transport,properties of QGP.At last,the coefficients ?mnk are defined to quantify the correlations among different flow angles.By studying the dependence of ?mnk on collision centrality and initial Npart,it is found that the dependence of ?422,?523,?6222 on system size is similar to that of ?2 and the dependence of ?633 on system size is similar to that of ?3.This demonstrates that the flow angle correlation coeficients?mnk are sensitive to the properties of the initial geometry.