Study Of Chiral Magnetic Effect And Charge Fluctuations In Relativistic Heavy-ion Collisions

One of the main proposes of high energy heavy-ion collisions is to study the states of nuclear matter under extreme conditions.The Relativistic Heavy Ion Collider(RHIC)at BNL and the Large Hadron Collider at CERN can accelerate nuclei to near the speed of light and collide them with other nuclei.It can create a new phase known as quark-gluon plasma(QGP).Therefore one of main tasks of relativistic heavy-ion collisions is to study the properties of the QGP.We mainly use a multiphase transport(AMPT)model to study and offer some explanations to the QGP-related phenomena in relativistic heavy-ion collisions experiments.This thesis mainly focuses two physical aspects,chiral magnetic effect(CME)and QCD critical end point(CEP).The spectators with really high velocities can create a very strong magnetic field.This can make the chiral fermions magnetized in the direction of the magnetic field.Quarks are left handed which means that their momenta and spin are in the same direction and right handed which means that their momenta and spin are in opposite directions.Under such a unique condition,the unbalance of number of chiral fermions can induce an electric current in the direction of magnetic field,i.e.,chiral magnetic effect.There are many experimental observables to detect the CME,but all of which have background contributions,which make the origin of the charge separation phenomenon observed in experiments in debate.We use the AMPT model to simulate Au+Au collisions and calculate the CME observable R_?m,and find that R_?mcan distinguish the background from the CME,because R_?mis flat if we only consider background,but concave if we introduce a CME-induced charge separation into the AMPT model.Besides,we also compare the responses of R_?mand?to the CME and analyze the sensitivities of those two observables to the CME signal strength.It was found that they both nonlinearly respond to the CME signal.This study can help us better understand the usefulness of the CME observables,which provides some guidance to search the CME in experiments.The study of the QCD phase diagram is a main focus in high energy nuclear physics.People have proposed many methods to search for the QCD critical end point,e.g.,light nuclei production,HBT-radii and the fluctuations of conserved charges.We use the AMPT model to study dynamical evolution and particle correlation of net-charge fluctuations in Au+Au collisions.We calculate the moments of net-charge multiplicity distributions,including mean,standard deviation,skewness and kurtosis.Those moments are well consistent with experimental data and we do not find any non-monotonous behaviour.We also study the stage evolutions of moment products and show the dynamics of moment products.We learn that the correlation between positively and negatively charged particles is positive by comparing the AMPT results with the expectations from Poisson distributions.This positive two-particle correlation may be caused by the different dynamical processes at different evolution stages.This study may provide a valuable view to understand the experimental measurements on net-charge fluctuations related to the search of the CEP in relativistic heavy-ion collisions.