The Event-by-event Analysis Of Transverse Momentum And Multiplicity Fluctuations Using The AMPT Model

The main purpose of high energy heavy-ion collisions is to study the properties of strongly interacting matter under extreme conditions of high energy densities.The physics of this very high energy scale is thought to be described by quantum chromodynamics(QCD).With the development of experimental technology and computer technology,one can explores the QCD phase diagram and study the phase transition boundary and critical point between hadronic matter and quark-gluon plasma(QGP).Since the fluctuations of physical quantities in freezing hadron system near the critical point are believed to be significantly enhanced,the event-by-event fluctuation is an important tool for localizing the critical point.However,the system volume variation is believed to strongly effect the fluctuations.To deal with this problem,the strongly intensive quantities,which are strictly independent of volume and of its fluctuations within the model of independent sources,were introduced.In this thesis the AMPT(a multiphase transport)model is used to simulate different nucleus-nucleus collisions at CMS energies from 7.7 Ge V to200 Ge V,and the properties of the strongly intensive quantities constructed by transverse momentum and multiplicity are studied.The combined event method is proposed to simulate the model of independent sources.The strongly intensive quantities are found to be independent of the number of original p+p events.The scaled strongly intensive quantities are introduced to partly eliminate the trivial correlations from nucleon-nucleon pairs.The results that are diverse in central Au+Au,Cu+Cu and C+C collisions become roughly consistent in peripheral collisions except for the lowest energy.The scaled strongly intensive quantities for peripheral collisions are approximate to 1 at most energies,indicating the combined event method could be introduced moderately to eliminate the trivial interpartical correlations.In this thesis the effects of different parameters on strongly intensive quantities are studied.The transverse momentum dependence is analyzed.The strongly intensive quantities within narrow intervals are less dependent on transverse momentum.The two strongly intensive quantities present saturation behavior as transverse momentum interval extends,which implies that particles with high transverse momentum have little con-tribution to the results.In the analysis of the dependence of pseudorapidity,there are obvious differences between the two strongly intensive quantities.Σ[P_T,N]is insensitive to the change of pseudorapidity,while△[P_T,N]is significantly dependent on pseudo-rapidity at low energies and weakly dependent on pseudorapidity at medium and high energies.The influences of dynamic processes are analyzed,Σ[P_T,N]is positively corre-lated with parton scattering cross section and depressed by the hadronic cascade process.The effects of parton cascade and hadron cascade on△[P_T,N]are non-monotonic.The effects of quantum statistics on the strongly intensive quantities are also analyzed.The results of numerical calculations and the AMPT model data analysis show that different quantum statistical laws can significantly affect the strongly intensive quantities,and the Fermi-Dirac statistics have less impact than the Bose-Einstein statistics.