The Azimuthal Angle Dependence Of Global Polarization In Au+Au Collisions At RHIC

It is believed that a strongly interacting,hot and dense medium known as Quark Gluon Plasma has been created in high-energy heavy-ion collisions at the Relativistic Heavy IonCollider(RHIC).In non-central collisions,the initial angular momentum associated with the receding spectators can be on the order of 1000h,and can be transferred to quarks through the spin-orbit coupling.Such effect can manifest itself via final-state hadrons and is detectable through the A(A)polarizat,ion and ?spin alignment.The STAR experiment at RHIC has observed for the first time a significant alignment between the angular momentum of the medium produced in non-central collisions and the spin of A(A)hyperons,revealing that the matter produced in heavy-ion collisions is by far the most vortical system ever observed.Such vorticity is expected to depend on hyperon's azimuthal angle,however,so far the theoretical guidances on the azimuthal angle dependence of global polarization are not con-sistent,due to various treatments on how spin is transp(orted in the fluid.Thus the experimental study of the azimuthal angle dependence of hyperon polarization can help us in understanding transport properties of the system and shed light,on dynamics in a highly vortical,low viscous environment.In this thesis,we analyze the experiment data in Au+Au collisions which was taken at the STAR experime.nt at RHIC.We reconstruct the A and A by using proton and anti-proton and measure the global polarization of A and A as a function of the azimuthal angle relative to the reaction plane in Au+Au collisions at(?)= 7.7.11.5,14.5,19.6,27,39,62.4,200 GeV.When to apply the event plane resolution to the dependence of azimuthal angle,we proposed a data-driven resolution correction method.A correction matrix could be determined by a toy model simulation based on the STAR data.After resolution correction,in 20-50%Au+Au collisions,the polarization is found to be largest in in-plane direction,but decrease with azimuthal angle,and decreases to zero in out-of-plane direction at(?)= 7.7,14.5,19.6,200 GeV.It indicates that the vorticity of the system is maximal in in-plane direction but minimal in out-of-plane.So far no models are able to reproduce the measurement.The strength of the azimuthal angle dependence shows a weak energy dependence.We generalize the data-driven resolution correction method to the measurement of the azimuthal angle dependence of ?meson spin alignment.We redefine the correction matrix,the correction method works by using a model simulation.The finite coverage can affect the measurement of ?meson spin alignment.We observed that the finite coverage can also affect the azimuthal dependence of spin alignment.It contains two parts,one is acceptance-driven geometry effect on the spin alignment,the other is acceptance-driven local spin alignment in in ?meson's helicity frame.We also take the possible local intrinsic spin alignment in ? meson's helicity frame into consideration.We mark these effects as ?00,accept geo,?00,accept HX,?00,instrinsic HX.We propose a data-driven correction method,by rotating the L in the three dimension,these effect can be removed,the real signal ?00,real can be extracted.This data-driven method was confirmed by a toy model simulation,and can be used on the data analysis.With the framework of the UrQMD model,by tracing the number of initial quarks in protons,we study the elliptic flow of protons with 3,2,1,0 initial quarks and anti-protons in Au+Au collisions at(?)=7.7,11.5,39,200 GeV.The difference of elliptic flow between protons with 2,1,0 initial quarks and anti-protons is smaller than 0 or consistent with 0,respectively.The difference of elliptic flow between transported protons(with 3 initial quarks)and anti-protons is larger than 0 at 7.7,11.5 and 39GeV.It shows a good agreement with the STAR results at 7.7 and 11.5 GeV,but overestimates the STAR results at 39GeV.The yield of transported protons with 3 initial quarks is smaller than that of protons with 2 and 1 initial quarks and the v2 of all protons is much smaller than the STAR results.The observation of the difference of elliptic flow between transported protons and anti-protons in the UrQMD model partly explains the v2 difference between protons and anti-protons observed in the Beam Energy Scan program in Relativistic Heavy Ion Collider(RHIC).