Study On The Dependence Of Vorticity In QGP Fluid On Smearing Velocity In High Energy Heavy-ion Collisions

In the standard model of particle physics,quantum chromodynamics(QCD)is the basic theory to describe strong interactions.The calculation of QCD shows that under the condition of high temperature and high density,the quarks and gluons confined in the atomic nucleus will meet the deconfinement condition,forming a new material form,which is called quark gluon plasma(QGP).The study of quark gluon plasma is one of the frontier problems in high energy physics,which is of great significance to understand the strong interaction and the evolution of the universe.And high energy heavy ion collisions can produce very high temperature,to achieve the required QGP release conditions.At the same time,huge orbital angular momentum and magnetic field will be generated in the peripheral collisions,and such huge orbital angular momentum will eventually be transformed into the extremely high vorticity in the QGP fluid.Under such extreme conditions,there will be many anomalous quantum transport phenomena,such as Chiral Magnetic Effect(CME)and Chiral Vortical Effect(CVE).The study of Chiral Vortical Effect depends on the understanding of vorticity in QGP fluid.The research content of this paper focuses on the calculation of the velocity field and the corresponding vorticity of QGP fluid generated in the peripheral high energy heavy ion collisions.In this paper,the peripheral high energy heavy ion collisions process is simulated by using an multiphase transport model(AMPT),and the evolution information of parton over time is obtained.Through the smearing function,the energy and momentum of the parton are smeared to any field point(t,(?)r),and the energy-momentum tensors information at this field point can be obtained.Then,various information of the fluid at this field point can be calculated,including velocity field,temperature field and vorticity,etc.However,in the past,the energy-momentum tensor at(t,(?)r)has been calculated by using the smearing function.It is often assumed that the smearing velocity is infinite and is considered to be instantaneous.In our calculation,we first adopted the calculation method of finite smearing velocity in line with the basic principle of quantum mechanics.The cone slicing algorithm based on Minkowski Space-time was successfully constructed,and the finite smearing velocity was equivalent to the cone surface in four-dimensional space-time.It is considered that only the parton on the conical surface can contribute to the energy-momentum tensor of the field point.Based on this framework,we calculate the dependence of velocity field,temperature field and vorticity evolution on smearing velocity in QGP fluid.Our calculation results show that these fluid properties show significant differences at different smearing velocities.In particular,the vorticity calculated at finite smearing velocity and infinite smearing velocity will present an inverse phenomenon,which is quite instructive for people to understand the sign puzzle in hyperon polarization caused by vorticity.