Effect Of Electromagnetic Fields In Relativistic Heavy Ion Collisions

Quark and gluon are the fundamental particles in the standard model.The quark-gluon plasma(QGP)that is believed to have existed in the Big Bang is produced in rel-ativistic heavy-ion collisions.Therefore it is important to study the quark-gluon plasma to understand the origin and evolution of the early universe as well as the basic structures of matter.The quark-gluon plasma provides an essential condition for some anomalous transport effects,such as the chiral magnetic effect,the chiral separation effect and the chiral magnetic wave.With the strong magnetic fields,a vector current can be caused by the difference between the left hand and right hand fermions,this is so called the chiral magnetic effect which can induce a charge separation.The chiral separation ef-fect is the adjoint side of the chiral magnetic effect and it can induce an axial current.Furthermore,the coupling of the chiral magnetic effect and chiral separation effect can induce the chiral magnetic wave which can cause an out-of-plane quadrupole.The elec-tric quadrupole leads to the second-order anisotropy coefficient₂that will present a linear dependence on the charge asymmetry_ch.In experiments,some measurements support the chiral magnetic effect and chiral magnetic wave.However,there exists the obvious background and not enough conclusive to prove their existences so far.Because the quark-gluon plasma is produced at the early stage in heavy-ion collisions,it affects observing them in experiments.Nevertheless,we can investigate the early collisions by using theoretical models.In this thesis,a multi-phase transport(AMPT)model is used to study the anomalous transport effects.On the one hand,the chiral magnetic effect in small systems should be different from that in A+A collisions but the recent experimental results from CMS find that results in+Pb collisions are similar to those in Pb+Pb collisions.So we study the electromagnetic fields and their spatial distributions as well as the correlation between the magnetic field and participant plane.We suggest that the chiral magnetic effect of small systems should be searched at low multiplicities.On the other hand,we also study the electromagnetic fields and their spatial distributions in the collisions of isobaric nuclei with different settings of the deformations.By studying the correlations between the magnetic field and participant plane or neutron spectator plane,we find that the correlation between magnetic field and spectator plane is stronger than the correlation between magnetic field and participant plane.The larger the deformation,the greater difference among the correlation between magnetic field and participant plane and the correlation between magnetic field and spectator plane.Because the spectator plane has much stronger correlation with magnetic field than participant plane,the?correlator with respect to the spectator plane can reflect much cleaner chiral magnetic effect signal.At last,we find that?distributions are dipole at the transverse plane for non-central Au+Au collisions.The coupling of dipole distributions and the magnetic fields can induce an electric quadrupole moment.It is similar to the electric quadrupole moment from the chiral magnetic wave.Moreover,the results of the centrality dependence of?from the collision zone are consistent with the slope parametermeasured by the STAR collaboration.The novel mechanism of electric quadrupole moment suggests a new interpretation for the STAR results of the charge-dependent elliptic flow of pions.The interactions among the partons reflect the properties of the quark-gluon plasma and the ZPC model which is an important part in AMPT model describes the two-body partonic interactions.Due to the geometrical interpretation of cross section,the causal-ity violation is inevitable in cascade simulations.Although the parton subdivision tech-nique can remove or reduce the causality violation,it will affect the event-by-event cor-relations and fluctuations and is also much more computationally expensive.We study the different collision schemes in the ZPC parton cascade inside a box and then com-pare these results with the results of parton subdivision.We have found a new collision scheme without using the parton subdivision technique.Even at the high opacity,the new collision scheme can accurately describe the transverse momentum and its time evolutions.We also study the ratio of the shear viscosity to entropy density and the results also validate the new collision scheme.In addition,we find a new parton subdi-vision technique in a box which is more efficient than the standard subdivision method.The subdivision factor of the new parton subdivision can be huge(e.g.10⁶)which is much higher than the standard subdivision factor.