The Calculation Of ?((?))'s Polarization And Vorticity In Heavy Ion Collisions

In the process of extreme relativity heavy-ion non-center collisions,strong angular momentum and magnetic fields will be generated along the direction of angular momentum.These extreme physical conditions will bring strange physical phenomena.In this thesis,we mainly study the polarization of the final state ? particles in the relativistic heavy ion collision,and the cause of the polarization separation between the positive and negative ? particles in the final state.In 2017,the STAR experimental group published an article announcing that during the energy scanning experiment,the polarization phenomenon of the positive and negative ? particles was observed.According to the "spin-vortex" coupling theory,the final state particles generated during hadronization will be polarized along the direction of angular momentum.But because the experiment can only observe the charged particles after baryon decay,it is very difficult to observe.Fortunately,when the ? particles decay into protons and ? mesons,they tend to emit protons in the direction of the spin.This gives the experiment Observing particle polarization establishes the possibility.This experiment proves that in the relativistic heavy ion collision,there is an extremely powerful velocity gradient in the system constructed by the participants-a vortex.However,the cause of the polarization of the final state ? particles is not limited to the "spin-vortex" coupling.The magnetic field will also make the ? polarize in the opposite direction of the magnetic field,making the anti-? particles polarize in the magnetic field direction.In order to study the polarization and polarization separation of ? particles.First,this article will introduce the results of various existing experiments,as well as the existing model prediction work.Based on this,we use the multiphase transport model AMPT to generate events,and make preliminary predictions and explanations of the origin of polarization from the perspective of the spatial-temporal distribution of ? particles and the spatial-temporal distribution of local vortices.Then,starting from the spin four vectors,we have an equation suitable for program calculations.After substituting into the calculation,it was found that it is impossible to clearly observe the polarization separation between positive and negative particles by relying only on the vortex effect.Finally,we introduced the spatiotemporal distribution of freezing temperature and magnetic field,successfully explained the polarization separation between positive and negative particles in the experiment,and gave a reference fitting formula for the lifetime of the magnetic field during heavy ion collisions.