Kinetic Freeze-out Temperature Of Interacting System And Transverse Flow Velocity Of Final-state Particles In High Energy Collisions

Transverse-momentum(pT)spectra of charged and neutral particles produced in proton-proton(p-p),proton-nucleus(p-A),and nucleus-nucleus(A-A)collisions at high energies are important quantities measured in experiments.In particular,collisions at the Relativistic Heavy Ion Collider(RHIC)and the Large Hadron Collider(LHC)have been providing us excellent chances to study the signals and features of quark-gluon plasma(QGP),the properties of multi-particle production,and the characteristics of interacting system.In the study of pT spectra,we can obtain some useful information which contain,but are not limited to,the effective temperature(T or Teff),chemical freeze-out temperature(Tch),and kinetic freeze-out temperature(T0 or Tkin)of interacting system,and transverse flow velocity(?T)of final-state particles.By studying T0 of interacting system and ?T of final-state particles,we can further understand the characteristics of transverse excitation and dynamical expansion of interacting system.Many models have been introduced in high energy collisions.These models can be mainly classified into two classes,hydrodynamic model and thermodynamic and statistic model.The hydrodynamic model describes mainly the system evolutions,focusing on the dynamic behavior of multiple particles.The thermodynamic and statistic model describes mainly the properties of produced particles,focusing on the collective or global statistical behavior of final-state particles.Both the hydrodynamic model and thermodynamic and statistic model describe partly interacting process and its products.In order to gain a deeper understanding for high-energy collision process,a simple statistical distribution(such as the Boltzmann or Tsallis distribution)is introduced in the hydrodynamic framework(such as the Blast-wave model).Then,the Blast-wave model with Boltzmann-Gibbs or Tsallis statistics is developed.The main works finished and the main conclusions obtained in this thesis contain two parts.In each part,abundant contents are included.Firstly,pT spectra of different types of particles produced in mid-rapidity interval in lead-lead(Pb-Pb)collisions with different centrality intervals,measured by the ALICE Collaboration at center-of-mass energy per nucleon pair(?)=2.76 TeV,are conformably and approximately described by the Tsallis distribution,The dependences of parameters(effective temperature,entropy index,and normalization factor)on event centrality and particle rest mass are obtained.The effective temperature extracted from pT spectra increases with increase of particle rest mass,and decreases with decrease of centrality.The source temperature at the kinetic freeze-out is obtained to be the intercept in the linear relation between effective temperature and particle rest mass,while the particle(transverse)flow velocity in the source rest frame is extracted to be the slope in the linear relation between mean(transverse)momentum and mean moving mass.It is shown that the source temperature increases with the increase of particle rest mass,which exhibits an evidence of mass-dependent differential or multiple kinetic freeze-out scenarios.We analyze the pT spectra of charged particles(?+,K+,P and p)produced in gold-gold(Au-Au)and Pb-Pb collisions over a(?)range from 14.5 GeV(one of RHIC energies)to 2.76TeV(one of LHC energies).For the spectra with a narrow pT range,an improved Tsallis distribution which is in fact the Tsallis distribution with radial flow is used.For the spectra with a wide pT range,a superposition of the improved Tsallis distribution and an inverse power law is used.Both the extracted T0 and ?Tincrease with the increase of(?),which indicates a higher excitation and larger expansion of interacting system at the LHC.Both the values of T0 and?T in central collisions are slightly larger than those in peripheral collisions.Secondly,we use five distributions(or models)to analyze the pT spectrum of charged particles(?±,K±,p,and p)and neutral particles(KS0)produced in central and peripheral large collision systems such as copper-copper(Cu-Cu),Au-Au,and Pb-Pb collisions,as well as in small systems such as deuteron-gold(d-Au),p-p,and proton-lead(p-Pb)collisions.The parameters T0 and ?T are extracted.The five distributions(or models)describe only the contributions of soft excitation process,which include the Boltzmann distribution,the Tsallis distribution,the improved Tsallis distribution,the Blast-wave model with Boltzmann-Gibbs statistics,and the Blast-wave model with Tsallis statistics.For the hard scattering process,the inverse power-law is uniformly used.That is,we use respectively the superposition of one of five distributions(or models)and the inverse power-law to describe the wide pT spectra.Our calculations show that T0 obtained by the Blast-wave model with Boltzmann—Gibbs statistics with the conventional treatment for central collisions is smaller than that for peripheral collisions,which is inconsistent with the results obtained by other models.We have given a reexamination for ?T in peripheral collisions in which ?T is taken to be?(0.40±0.07)c.After reexamination,this model shows approximately consistent results with other models.The result that the central collisions have a larger T0 renders more deposition of collision energy and higher excitation of the interacting system due to more participating nucleons taking part in the violent collisions.From the RHIC to LHC,the slightly increased or nearly invariant T0 renders the limiting or maximum deposition of collisions energy.The study on ?T shows that,from central to peripheral collisions and from the RHIC to LHC,the slightly increased or nearly invariant?T renders the limiting or maximum blast undergone by the interacting system.For small systems,comparing with central nuclear collisions,p-p collisions are closer to peripheral nuclear collisions.In addition,we collect the yields of ?-and ?+,K-and K+,as well as p and p produced in mid-rapidity interval(in most cases)in central Au-Au,central Pb-Pb,and inelastic or non-single-diffractive p-p collisions at different collision energies.The chemical potentials of light particles and quarks are extracted from the yield ratios,?-/?+,K-/K+,and p/p,of negative to positive particles over an energy range from a few GeV to above 10 TeV.The dependences of chemical potentials on collision energy are studied.Comparing with those at other energies,the chemical potentials show and the yield ratios do not show different behaviors at a few GeV(?4GeV),though the limiting values of the chemical potentials and the yield ratios at very high energy are 0 and 1 respectively.