Fluctuations And Quarkonia In High Energy Nuclear Collisions

The study of QCD phase transition can help us learn more about the strong interaction, and the quark gluon plasma created in relativistic heavy ion collisions is an important experimental realization of the QCD phase transition. We will discuss the fluctuations and signals of the QCD phase transition from different aspects.Firstly, we will employ the equation of state of the hot and dense matter in holographic QCD model, which is one of the strongly coupling models, to calculate the statistical fluctuations. By analyzing them, we can learn more about the fluctuations of the strongly coupling systems, and try to get some common behaviors. We hope these can provide more information about the critical phenomenon of the QCD phase transition.Then, we consider how a small fluctuation of the QGP evolves on top of some known background. We treat these fluctuations as perturbations, and linearize the ideal hydrodynamic equations. By solving the equations, we can learn how an fluctuation evolves.What’s more, we consider the meson bound states inside the QGP. We employ the potential model with screening effect in the framework of two-body Dirac equations, to calculate the quark-antiquark bound states at finite temperature, and determine their melting temperatures. Taking the melting temperature as the freeze-out temperature in CooperFrye model, we can calculate the elliptic flow of the thermally produced particles. We find a sequence of the mesons’ melting temperatures: Tc< Td（φ） — Td（D） < Td（J/ψ）,which qualitatively fits the experimental data.Finally, we study the quarkonium bound states in the extremely strong magnetic fields generated in heavy ion collisions, and analyze how the magnetic field affects quarkonium states. We also calculate how high pTcˉc pairs evolve in a magnetic field with finite lifetime, and how their distribution changes. We find that the magnetic field makes the quarkonium bound states no longer the eigenstate of spin or orbital angular momentum. What’s more, a meson moving in a magnetic field is with a non-zero electric dipole generated by the Lorentz force. We also find that the magnetic field leads to a — 4%enhancement of the high pTJ/ψ mesons, as well as a non-collective v₂— 4%.