Simulation Analysis Of Elliptic Flow At RHIC Energies

One of the goals of high energy heavy ion collisions is to produce and study theproperties of nuclear matter under high pressure and high temperature. One of the mostimportant findings at RHIC (Relativistic Heavy Ion Collider) experiments is the produc-tion of the strongly coupled quark and gluon plasma (QGP). The consistency of the largeelliptic ?ow predicted by ideal hydrodynamics with experimental measurements and thequark number scaling of hadronic elliptic ?ow are the most important evidences. Ellip-tic ?ow is sensitive to initial geometry, equation of state and dissipative properties of thesystem. Elliptic ?ow is an important physical observable for studying the properties ofcollision system at early stage in evolution. AMPT (a multiphase transport) model in-cludes the incomplete equilibration and dissipative properties of quark mater produced atearly stage in nucleus nucleus collision, and could describe the elliptic ?ow data at RHICwell. AMPT model is used to simulate nucleus nucleus collision at RHIC energies in thisthesis to study elliptic ?ow and obtain the properties of system at early stage.The time evolution of integral elliptic ?ow of total quark, freeze-out quark and ac-tive quark are studied. Contrast to the gradual increasing integral elliptic ?ow of totalquark and active quark, the integral elliptic ?ow of freeze-out quark decreases at earlystage and increases at late stage. By studying the distribution of position and velocityof freeze-out quark in transverse plane, the characteristic evolution of the integral ellip-tic ?ow of freeze-out quark could be attributed to the surface emission of quark at earlystage. By studying the elliptic ?ow of quark freezing out at early stage and quark with lesscollisions, the saturation of differential elliptic ?ow of quark at large momentum could beattributed to surface emission. For collisions with fixed impact parameter but differentcross sections of quark, the integral and differential elliptic ?ow of quark freezing out atearly stage approaches to saturation. However, the integral and differential elliptic ?owof quark freezing out at late stage increases largely with cross section for the conditionsstudied in this thesis. The variance of the multiplicity of freeze-out quark with time isstudied. Although the multiplicity of quark affected by surface emission decreases withcross section, surface emission is still an important effect at RHIC energy.The relation between elliptic ?ow of quark and hadron is studied. The phase space correlation of quark and the internal Wigner function of hadron are shown to be impor-tant for elliptic ?ow. The elliptic ?ow of hadron produced through quark coalescenceis studied for quark's phase space correlation produced by quark's free streaming. Boththe theoretical and numerical calculation leads to the conclusion that the hadronic elliptic?ow could be nonzero even though the elliptic ?ow of quark is zero in quark coalescencemodel. The hadronic elliptic ?ow produced in quark coalescence is sensitive to the phasespace correlation of quark and the size of hadron. Quark free streaming is implementedin AMPT model. The conclusion that the hadronic elliptic ?ow could be nonzero forvanished elliptic ?ow of quark is supported by the model data. The hadronic elliptic ?owproduced through quark coalescence is 30% of that for collision with cross section equalto 10mb under RHIC conditions.The relation between eccentricity scaled elliptic ?ow and incomplete equilibrationof system is studied. The AMPT model data for collisions with fixed impact parameterbut different cross sections could be described well by a formula in reference. The hydro-dynamics limit of elliptic ?ow could be obtained by fitting model data with the formula inreference, and the deviation of elliptic ?ow of model data from its hydrodynamics limit iscalculated. The effects of quark coalescence, hadronic interaction and resonance decay onthe deviation of elliptic ?ow from its hydrodynamics limit are studied. The finding thatthe ratio of hadronic elliptic ?ow to that of quark decreases with cross section leads toless deviation of hadronic elliptic ?ow from its hydrodynamics limit. For collisions withdifferent cross sections and collision energies, variation of the elliptic ?ow of the modeldata with different centralities could not be described well by the formula in reference.With the modified calculation of Knudsen coefficient in this thesis, the variation of elliptic?ow of quark with centrality for different collision energies and cross sections could bedescribed well.