Investigating The NCQ Scaling Of Elliptic Flow At LHC With AMPT Model

Quark-Gluon Plasma(QGP)is the state of nuclear matter formed in high tem-perature and high density.In the experiment,the properties of this hot,dense nuclear matter can be constrained through a wide range of measurements in the high energy heavy-ion collisions.An important experimental probe in this quest is the anisotropic flow of final state particles.The anisotropic flow can be obtained with the Fourier expansion of the azimuthal distribution of emitted particles in the transverse momentum space.The second-order coefficient is the elliptic flow(v2),which shows a strong centrality dependence.It receives considerable attention and plays an essential role in studying the collective motion of the QGP.The transverse momentum(pT)dependence of v2 can be used to study many properties of QGP.At low pT,for a given pT value,v2 of different particles are observed to be ordered by mass with heavier particles showing smaller v2 and vice versa.In the intermediate pT region,the pT differential v2 of particles tend to group based on their hadron types,baryons or mesons.However,at high pT,v2 value reflects the energy loss when the high energy jet traverses the QGP.More intriguingly,it is predicted in the quark coalescence mechanism that v2 of different hadrons,when scaleby the number of constituent quarks,could ap-proximately exhibit a uniform behavior with pT/nq(NCQ scaling).This feature has been observed at RHIC with surprising accuracy.This finding is considered to be an evidence that the quark coalescence mechanism plays an important role in the hadronization process of QGP.However,both PHENIX and ALICE experiments have reported the violation of the scaling properties in heavy-ion collisions.The origin of this violation is still unknown at this moment.In this work,we perform a systematic study of the possible effects contributing to the violation of v2 NCQ scaling at LHC with a multiphase transport model(AMPT).First,we review briefly the methods to calculate the elliptic flow v2,and what can be described in the AMPT model.On the next step,with the variation of the fragmentation parameters,collision centrality and system energy,we find that the initial conditions of parton dynamics are important for the existence of NCQ scaling when the hadronic interaction is off in Pb-Pb collisions.Based on one set of initial conditions that conserve the v2 NCQ scaling,we can explore the effect introduced by the final state hadronic rescatterings.It is found that the impact to the hadronic v2 depends on its particle type,one may expect sizable contribution to scaling violation from hadronic evolution stage.In summary,we examine systematically in this work the possible size and contribution to v2 scaling violation at different stages.Our findings may shed a light to help us form a comprehensive understanding to the origin of violation at the LHC energy scale.