Properties Of Minimal Condensed Matter Produced In High Energy Collisions

Quark-Gluon Plasma(QGP)is a kind of liquid condensed matter formed under conditions of extremely high temperature or extremely high density.As predicted by Quantum Chromodynamics(QCD),QGP may exist in the early universe and the inner core of neutron stars.Besides,QGP can also be found in high energy heavy-ion collision experiments.Due to the properties of strong coupling and low viscosity,QGP is called as "perfect fluid".Phase transition from QGP to color superconductivity occurs in the high baryo-chemical potential and low temperature regime.The volume of the QGP produced in high energy heavy-ion collisions is so minimal(several thousands of fm3)and the lifetime of the QGP is so short(dozens of fm3/c)that people cannot measure its properties directly and only can study its properties based on the analysis of the finial-state particles produced in the QGP hadronization process.In this thesis,in the framework of multisource thermal model,we study the transverse momentum or transverse mass distributions of several light final-state particles produced in different collision systems at different energies from AGS to LHC with a two-component Erlang distribution or Tsallis-Pareto-type function,obtain the yield ratios of negative to positive particles from the normalization con-stants,extract the chemical potentials of several light hadrons and quarks from the yield ratios,analyze the dependences of chemical potentials on nucleus size,colli-sion energy,and centrality,then extract the critical collision energy of phase tran-sition from hadronic matter to QGP matter and discuss the properties of QGP with QCD.We analyze the yield ratios of negative to positive particles produced in cen-tral nucleus-nucleus collisions,and find that the logarithmic functions of three yield ratios show obvious linear dependence on the reciprocal of collision energy(center-of-mass energy).Based on the above linear relationships,the chemical potentials of particles are calculated and are solved analytically to get the maximum at 3.526 GeV,which maybe the critical collision energy of the phase transition from hadron-ic matter to QGP matter.When the collision energy is larger than 3.526 GeV,the absolute of chemical potential decreases with increase of collision energy and ap-proaches to zero at very high energy,which implies that the lifetime of QGP matter may be longer comparing with gas-like quark matter,and the particle number den-sity is lower for the expansion of the QGP before the stage of chemical freeze-out.Meanwhile,it indicates that the partonic interactions possibly play an dominant role at RHIC and LHC,especially at LHC.From the comparative analysis of energy-dependent chemical potentials of light hadrons(?,K and p)and quarks(u,d and s)both in central nucleus-nucleus and inelastic proton-proton collisions,we find that?? is positive in pp collisions,and is negative in cental nucleus-nucleus collisions,and the change of ?? with collision energy is opposite.While,the change trends of the other five types of chemical potentials(?K,?p,?u,?d,and ?s)with collision energy are the same in the two kind of collision systems,and can be described by one unitive equation.Furthermore,like that in pp collisions,?? in d-Au collisions is positive,which shows that the size of collision system has a certain influence on QGP properties.By analyzing the chemical potentials of the light final-state particles producedin Au-Au,Pb-Pb,and d-Au collisions in different centrality classes,we find that the absolute of chemical potential for most particles decreases with the increase of centrality interval,where ?p has the largest range of change and relative change and has a very significant pattern of change.The ratio of particle yield to partici-pant number is smaller in peripheral collision than that in central collision,which shows that the decrease of chemical potential for peripheral collision system results from the decrease of particle number density of QGP produced in the early stage of collision.Meanwhile,based on the study of Au-Au collisions at 7.7 to 62.4 GeV in different centrality intervals,we find that the logarithmic function of yield ra-tio shows obvious linear dependence on the reciprocal of collision energy for each centrality,and the absolute of the slope of the linear relationship decreases with increase of centrality interval,which reveals that the critical collision energy is not dependent on centrality and the QGP matter with larger particle number density is dependent on collision energy.In addition,according to the analysis of the transverse momentum or trans-verse mass spectra of final-state light particles(?±,K±,p,and p)produced in dif-ferent collision systems(p-p,d-Au,Au-Au,and Pb-Pb)by two-component Erlang distribution,the final-state light particles in different collision systems at differ-ent energies in different centrality are mainly produced in soft excitation process and hard scattering process,where the soft excitation process is formed of several quarks and gluons after intense collisions,and the hard scattering process is formed in more intense head-on collisions between two valence quarks.The study shows that the contribution ratio of soft excitation process is more than 50%or even more than 90%,which indicates that the contribution ratio of soft excitation process is more than that of hard scattering process,and the transverse excitation degree of interacting system is mainly determined by soft excitation process.