The Anisotropic Radial Flow And Shear Viscosity In Relativistic Heavy Ion Collisions

Quantum Chromodynamics (QCD) predicts that a new formed matter—Quark Gluon Plasma (QGP) is produced at extremely high temperature and density environ-ment. It consists of a large amount of deconfined quarks, antiquarks and gluons, and exists in a few millionths of a second after the Big Bang. QCD is a theory of the strong interaction describing the interactions between quarks and gluons. It enjoys two peculiar properties, the one is "quark confinement", the other is "asymptotic freedom". Under general conditions, free quarks cannot be observed due to the nature of "quark confinement". In the1970s, T.D.Lee et al. proposed that high energy heavy ion colli-sions may provide an opportunity for us to study the properties of strongly interacting matter at high temperature and densities—the quark-gluon plasma (QGP). In the past few decades, physicists have been looking for this new formed matter. As a result, the high energy heavy ion collision physics development faster and faster.The Relativistic Heavy Ion Collider (RHIC) located at Brookhaven National Lab-oratory (BNL) in U.S. was build and run successfully for the first time in2000, with collision energy to200GeV/nucleon. A large number of experimental data showed that there exist the new formed matter—QGP. The observation of large elliptic flow at RHIC is considered as one of the most important signatures for the formation of the strongly interacting Quark Gluon Plasma (sQGP). The behavior of elliptic flow has been suc-cessful described by hydrodynamic models. This shows that the formed matter behaves like an almost-perfect fluid. The number-of-constituent-Quark (NCQ) scaling of elliptic flow observed at intermediate transverse momentum indicated that the partonic collec-tivity is measured at RHIC. Besides, jet quenching is anther main signature to claim the discovery of QGP at RHIC.The elliptic flow is the second Fourier coefficient of the azimuthal multiplicity distri-bution. It arising from the density gradient of the overlap area of two incident nuclei in non-central collision. The multiplicity distribution of azimuthal angle counts the num-ber of particles emission in a certain azimuthal angle. But the expansion of the system results in not only the anisotropy of multiplicity distribution but also their associate radial (transverse) momentum. The total radial momenta at a given azimuthal angle is the combination of them. Therefore, the azimuthal distribution of radial momentum should be a more sensitive measure of the anisotropic expansion. In the third chapter of this thesis, the azimuthal distributions of radial (transverse) momentum, mean radial momentum of final state particles are suggested for relativistie heavy ion collisions. Us-ing the sample of Au+Au collisions at (?)SNN=200GeV produced by AMPT model, we find that the azimuthal distribution of radial transverse momentum indeed counts the anisotropy of final state particles and their associated transverse momenta. Thus it presents a full description of anisotropic expansion at various centralities.As we know, the system created in heavy ion collisions expands and cools in a very short time. When the system is formed, the entire energy is the thermal energy. During the evolution of the system, some part of the thermal energy transform to the collective flow energy. So the thermal energy and the collective flow energy are both contribute to the total energy of the final state particles. And the thermal energy of a particle depends on the temperature and the mass of the particle. We suggest the azimuthal distribution of mean transverse (radial) rapidity of the final state particles as a more direct measure of the transverse motion of the source than the standard azimuthal multiplicity distribution. Using a sample generated by the AMPT model with string melting, the suggested distribution and its particle mass and centrality dependence are presented. These show that the isotropic and anisotropic parts of the suggested distribution behave as the expected radial flow (with a random thermal component), and anisotropic radial flow, respectively. Using a generalized blast-wave parametrization, we further extract the temperature and radial flow parameters from the same sample. It is found that the parameter of anisotropic radial rapidity coincides with the azimuthal amplitude of the suggested distribution.Moreover,the shear tension of viscosity in hydrodynamics is supposed to be propor-tional to the gradient of radial velocity along the azimuthal direction, which is directly related to anisotropic radial velocity. The proportionality constant is the shear viscos-ity. In this paper, the neighboring azimuthal bin-bin multiplicity correlation pattern is suggested, which is used as a good probe for the internal layer-to-layer interaction of the formed matter at relativistie heavy ion collisions. Then, the relation between correlation pattern and shear viscosity is derived. As a example, We use AMPT model to estimate the shear viscosity. Two samples for different cross section σ=3mb and σ=6mb have been analyzed. Our results are in qualitative agreement with the theoretical calculation from microscopic interactions, i.e., the larger scattering cross section, the smaller shear viscosity. Furthermore, applying this suggested measure of shear viscosity in current relativistic heavy ion collisions is looking forward to.