Fractal Behavior And Elliptic Flow Effect In Heavy Ion Reactions

Heavy ion collisions at intermediate and high energies are interesting subjects in theoretical and experimental nuclear physics because these collisions can provide a unique opportunity to investigate the particle productions,interacting mechanisms,and rare phenomena at high density and high temperature.Experimentally,fractal structure of slow particles from nuclear reactions in emulsion induced by ¹⁶O and ²⁴Mg at 4.5A GeV/c are studied in Chapter 3 by using factorial moments and Takagi moments.After the calculation of horizontal factorial moments and vertical factorial moments,it is found that the same conclusion can be attained although the results of the two kinds of methods are not equal.For nonflat multiplicity distributions,an extra M-dependent correction factor and a new variable are introduced to correct the factorial moments respectively.It is found that the new variable is better than the correction factor,under the new variable the horizontal factorial moments and vertical factorial moments are almost equal.The generalized dimensions can characterize the fractal behavior.The generalized dimensions of slow particles determined by factorial moments and Takagi moments are calculated.Multifractality of slow particles is observed in emission angle space.Self-affine fractal is a good candidate for descriptions of multiparticle production.Two-dimensional factorial moments of target fragments for ¹⁶O-AgBr collisions at 4.5A GeV/c are calculated in Chapter 4.Self-affine fractal is observed in target fragments.This phenomenon has been confirmed in some experiments.But an unambiguous conclusion can not be attained in some experiments.An in-depth study on the emission of target fragments is necessary.The occurrence of distinct minima inλ_q at q=3 indicates the possibility of a non-thermal phase transition in the emission process of target fragments in high energy nucleus-nucleus collisions.Theoretically,using a unified description on multiplicity distributions of final-state particles,the spallation residues in ⁵⁶Fe+p reactions and fragmentation products in ¹³⁶Xe(¹²⁴Xe)+Pb reactions at intermediate energy and at the low end of high energies are studied in Chapter 5.The isotopic production cross sections of fragments produced in the reactions are calculated by using a multisource ideal gas model.It is found that the MSIG model can well describe the experimental results,and the parameters can be explained well too.Each source contributes to multiplicity-like distribution of neutrons like a radioactive object.In high energy nucleus-nucleus collisions,the particle azimuthal anisotropy and its dependence on particle identity and on transverse momentum can provide information on the properties of interacting system. The dependences of elliptic flows on transverse momentum for identified particles produced in nucleus-nucleus collisions at high energy are studied in Chapter 6 by using the MSIG model that describes the distribution of transverse momenta as a Rayleigh-like distribution.The experimental results of Au+Au collisions at s^1/2=200A and 62.4A GeV and Cu+Cu collisions at s^1/2=200A GeV,measured by the STAR and PHENIX collaborations,are well described by using this model.