Transverse Momentum Distribution Of Final-state Products And Kinetic Freeze-out Temperature Of Interacting System In High Energy Collisions

Evolution of heavy ion collision system at relativistic heavy ion collider ?RHIC? and large hadron collider ?LHC? energies forms an extreme high-density and high-temperature condition and results in the creation of quark-gluon plasma ?QGP or quark matter?. Concomitantly, a lot of final-state products ?particles and jets? are produced in final state. By studying the transverse momentum spectra of various types of final-state products can explore the production mechanisms of particles and jets, the properties of the new state matter QGP, and the evolution process of interacting system, especially at the stage of kinetic freeze-out. Researching temperature of interacting system can study the transverse excitation degree of interacting system at RHIC and LHC energies and the contributions of soft excitation process and hard scattering process, and can provide the basis for a better understanding of the excitation degree of interacting system in ultra-high energy region.In this thesis, in the framework of multisource thermal model, we study different transverse momentum distributions of different final-state products produced in different collision systems at RHIC and LHC energies, extract the effective temperature and kinetic freeze-out temperature of interacting system, analyze the excitation degree of collision systems at the stage of kinetic freeze-out, and obtain the spatial structure pictures of interacting system.Under the assumption of equilibrium or local equilibrium state, we use the multi-component standard distribution, multi-component Erlang distribution, Tsallis-standard distribution, and Tsallis distribution to describe the transverse momentum spectra of different light particles and hadronic jets produced in proton-antiproton ?p-p?, proton-proton ?p-p?, and nucleus-nucleus [copper-copper ?Cu-Cu?, gold-gold ?Au-Au?, lead-lead ?Pb-Pb?, and proton-lead ?p-Pb?] collisions at RHIC and LHC energies. Three effective temperatures are extracted directly from three distributions. Meanwhile, an effective temperature corrected by Rayleigh and a new defined effective temperature are also extracted from average transverse momentum. The dependences of effective temperatures on particle type, center-of-mass energy, collision centrality, and nuclear size are analyzed. Then, the production mechanism of particles, the excitation degree of interacting system, the contribution ratios of soft excitation and hard scattering processes, and the effect of QGP on collision system are discussed. This study shows that the effective temperature extracted from transverse momentum spectrum of light particles is lower than that from jets. Effective temperature of collision system has a strong dependence on model. Although the values of effective temperatures extracted from different models are different, the dependent laws on collision system reflected by different temperatures are consistent with each other. Generally, the effective temperature increases with increases of particle mass, center-of-mass energy, collision centrality, and system size. However, the QGP produced in nucleus-nucleus collisions would prevent the increasing tendencies of effective temperature on center-of-mass energy, collision centrality, and system size, or even make the amount of change appearing to zero. For jets, the study shows that in a relatively complicated interacting system, there is a jet quenching effect, which is due to high energy quark and gluon jets going through a hot dense matter and suffering massive energy loss. And the higher the collision centrality is, the more obvious the effect is.The contribution ratio of soft excitation ?hard scattering? process is reflected by the weight factor k₁, ?k₂? corresponding to the first ?second? component in the two-component distribution. Our analysis shows that, in particle transverse momentum spectrum, low transverse momentum region corresponds to a soft process, and high transverse momentum region corresponds to a hard process. Low transverse momentum jets are formed of several quarks and gluons after intense collision or high energy parton jets after suffering massive energy loss through hot dense QGP matter, while high transverse momentum jets are created in the more intense head-on collisions between two valence quarks. Final-state light particles in low transverse momentum area are mainly from QGP ?or usual hadronic matter?, while light particles in high transverse momentum area are from jets. This study shows that the excitation degree of collision system is mainly determined by the soft excitation process, which means that the contribution ratio of soft excitation process is greater than that of hard scattering process. In fact, the contribution ratio of soft excitation process is more than 50% or even 99%. Similarly, soft excitation contribution depends on particle type, center-of-mass energy, collisions centrality, and nuclear size. And the higher the energy and centrality are, the greater the hard yield is. In nucleus-nucleus collisions, the more complex the system is, the more intense the hard process is. However, due to QGP blocking, the soft yield increases and the hard yield decreases. The decrements of hard yields corresponding to heavy particles and central collisions are large, and the more complex the system is, the more serious the hard yield decrement is.It is shown that the effective temperature extracted from particle transverse momentum spectrum contains the thermal motion and the influence of flow effect. The transverse momentum spectra of final-state light particles produced in nucleus-nucleus and proton-proton collisions at 0.2-7TeV are analyzed by the multi-component Erlang distribution and Tsallis statistics. Based on relations among average transverse momentum, average momentum, effective temperature, and particle rest ?and moving? mass, the kinetic freeze-out temperature and average transverse flow velocity are successfully extracted by a new method. In addition, three kinetic freeze-out temperatures and three average transverse flow velocities from Tsallis-standard, Tsallis, and standard distributions are obtained, and the dependencies of kinetic freeze-out temperatures and average transverse flow velocities on model and collision system are discussed. It is found that the kinetic freeze-out temperature has a great dependence on model selection. Although the kinetic freeze-out temperature extracted from the standard distribution is obviously higher than those from the Tsallis-standard and Tsallis distributions, the dependent laws on collision system reflected by the three kinetic freeze-out temperatures are consistent with each other. Average kinetic freeze-out temperatures slightly increase with increase of centrality, or have no significant change within the error range. Meanwhile, temperatures do not depend on center-of-mass energy and system size. In addition, the average transverse flow velocity of particles does not depend on model selection. From p-p, Cu-Cu, Au-Au, Pb-Pb, and p-Pb collisions at 0.2-7 TeV, the most values of average transverse flow velocity are in 0.35-0.53c, and their average value is 0.431c. There is a slightly increasing trend of the average transverse flow with increase of center-of-mass energy, collision centrality, and system size.In addition, the spatial structure pictures of interacting system in non-single diffraction ?NSD? p-Pb collisions at 5.02 TeV at the stage of kinetic freeze-out in rapidity, momentum, and velocity ?coordinate? spaces are extracted from transverse momentum and pseudorapidity distributions in the multisource thermal model. Some other distributions and the contributions of the target Pb-cylinder and projectile p-cylinder are also obtained. The contributions of the two cylinders are obviously different in the small yT ?rapidity definated in transverse direction? and |y_1,2| ?rapidity definated in x or y direction? region, and the two contributions are similar in the middle-large yT and |y_1,2| region. The densities in small |y_1,2| ?momentum components |px,y,z|? and yT ?transverse momentum pT? regions are larger than those in large |y_1,2| (|p_x,y,z]) and y_T ?p_T? regions. There are some zero density regions in the rapidity spaces due to the limitations of kinetics. In velocity ?coordinate? spaces, the densities in small |?_x,y| ?velocity components? and ?_T ?transverse velocity? regions and large region are larger than those in large |?_x,y| and ?_T and small |?z| region. The maximum scattering plots of particles in the coordinate space form a rough sphere which has high densities in the near surface regions towards the two beam directions.