Study Of Chiral Anomaly And Spin Alignment In Heavy Ion Collisions

In relativistic heavy ion collisions two nuclei,each traveling with close to light speed,collide with each other and create a matter resembling the early state of our uni-verse right after the Big Bang.Such state of matter,namely the quark gluon plasma(QGP),consist of free quark and gluon and is dramatically different from the universe that we line in today.From the study of QGP,we can learn the evolution of our universe and deepen the understanding of strong interaction between matters.The interaction be-tween matters can be classified into four types,namely the strong interaction,weak interaction,electromagnetic interaction and gravity.The quark gluon plasma is the idea test ground for strong interaction due to de-confinement of quarks and gluon.In strong interactions,there is no symmetry requirement from theoretical point of view,but no symmetry broken has been observed in experiment so far.On the other hand,our universe has more matters than anti-matters,it directly reflects the conse-quence of the somehow asymmetry of strong force.The first part of this thesis is related to the local CP violation of strong interaction,which gives rise to the Chiral Magnetic Effect(CME).This chiral anomaly has been proposed for more than decades but it has not been proven experimentally so far.The main difficulty in experimental study comes from the ambiguity of contributions from various kinds of backgrounds.In this work,we use a novel correlator which based on the examination of the momentum balance between particles due to the fact that CME will introduce a unbalance to momentum distribution of particles in final state.The chiral anomaly which comes from local CP violation will produce an electric dipole in the presence of magnetic field,the exper-imental observable is based on the difference in the first order harmonic coefficiency of the azimuthal angle expansion between positively and negatively charged particles.The methods employed in this work is based on the momentum balance for the first time,which dose not directly depend on the harmonic coefficiency mentioned above.Besides,in this paper we give a underlying relation between all other methods thus we can compare results from other groups with a meaningful reference point.The second part of this work is related to the study of Chiral Magnetic Wave.The Chiral Magnetic Wave is the collective excitation of the coupling between Chiral Mag-netic Effect(CME)and Chiral Separation Effect(CSE).Like the electromagnetic wave,the CME will introduce CSE,and CSE will give rise of CME and finally bring a electric quadrapole to the system.From flow study of QGP,we know the charge type which is closer to the reaction plane will have a larger elliptic flow,thus one can expect a differ-ence in second harmonic coefficient between oppositely charged particles.The second order harmonic flow is called the elliptic flow,and one uses the charge asymmetry de-pendent elliptic flow to identify CMW in experiment.In this work,we firstly point out that the charge asymmetry of an event depends on acceptance of detector,which may lead a bias to CMW study.Therefore,we propose a charge asymmetry free correla-tor.This novel correlator is based on the fluctuation nature of CMW,this additional fluctuation comes from the genuine CMW property and is different from statistical fluc-tuations.This additional fluctuation will boost event level distribution of elliptic flow,which include both statistical fluctuation and CMW contribution.Meanwhile,we use a charge shuffled events as reference,which is expected to be free from CMW influence.The third part of this thesis is related to the global polarization in relativistic heavy ion collisions.In semi-central collisions,nucleon will contribute a non zero orbit an-gular momentum to QGP,which will polarize the system in the direction perpendicular to reaction plane.The orbit angular momentum may polarize quark though spin-orbit coupling,and polarize vector mesons though quark coalescence.Studying the global polarization can provide additional dynamical information about the hot and dense mat-ter.The experimental measurements have been performed over many years,the main puzzle comes from the difference of observed signal between ? meson and K*meson.In this work,we point out that the hadronic scattering effect may give contribution to this difference.