Extracting Speed-of-sound And String Tension Parameters In High Energy Collisions

The systems of high energy heavy ion(nucleus-nucleus)collisions at the Relativistic Heavy Ion Collider(RHIC)and the Large Hadron Collider(LHC)can provide the highest temperature and density environment and condition.Under the extreme condition,a new state of matter,that is the quark-gluon plasma(QGP),which exists only in a very short time is formed in the evolution process of collision system.The QGP cannot be directly observed and measured in experiments because of its very short lifetime.Forturnally,many charged particles and neutral particles are produced in final state of high energy collisions,and they carry the abundant information of the evolution of collision system.The spectra of pseudorapidities,rapidities,and transverse momenta are important quantities which can be mesaured in experiments.Studying the different kinds of spectra of the final-state particles can help people to deduce the property of QGP and the interaction mechanism between the partons.In this thesis,the multiple spectra of the final-state particles produced in high energy collisions are systematically described and studied by more than one theoretical models and statistical methods.The main contents finished in this thesis can be divided into three parts.i)The idea of multisource is introduced in the Landau hydrodynamic model.Then,a revised version of the model is obtained.This new revised Landau hydrodynamic model is consisted of three parts which include a large enough central source which can be described by the Landau hydrodynamic model and a target(projectile)source which emits isotropically particles in its rest frame.Using the Monte Carlo method,the pseudorapidity spectra of final-state particles produced in gold-gold(Au-Au),copper-copper(Cu-Cu),lead-lead(Pb-Pb),deuteron-gold(d-Au),gold-emulsion(Au-Em),proton-emulsion(p-Em),proton-proton(p-p)and proton-antiproton(p-(?))collisions at high energies are described.The modeling results are in agreement with the experimental data of international collaborations.In the descriptions,the values of squared speed-of-sound(c2s)are obtained and found to be in the range from 1/3 to 1/2 for the central source and less than 1/3 for the target(projectile)source.This implies that the central source undergoes the phase transition from the hadronic gas to the QGP liquid and the target(projectile)source stays in the state of hadronic gas in the evolution of collision system.ii)Using the same revised Landau hydrodynamic model,i.e.using the Gaussian function for the central,target,and projectile sources,respectively,the sum weighted by the three functions can analytically describe the rapidity spectra of negatively charged mesons produced in p-p and beryllium-beryllium(Be-Be)collisions at the Super Proton Synchrotron(SPS)energies and(net-)protons produced in Au-Au and Pb-Pb collisions over an energy range from the Alternating Gradient Synchrotron(AGS)to RHIC.The modeling results are in agreement with the experiment data of international collaborations.In particular,the excitation function of the squared speed-of-sound,i.e.the dependence of squared speed-of-sound on energy,is studied.It is found that a local minimum in the excitation function appears at 8.8 GeV,which renders the soft point in the equation of state.This local minimum is expected to be related to the critical energy of quark deconfinement and QGP phase transition.It should be noted that the squared speed-of-sound is not extracted from the rapidity spectra of(net-)protons due to they being contributed by the whole participant region and obeying the conservation of baryon numbers which is beyond the Landau model.iii)Using a two-component Erlang distribution and a two-component Schwinger mechanism,the transverse momentum spectra of J/? and ? mesons produced in p-p,proton-lead(p-Pb),and Pb-Pb collisions at LHC energies,as well as (?),?,and negatively charged particles produced in Au-Au collisions at RHIC energies,are studied.The model results are in agreement with the experiment data of international collaborations.In particular,the mean transverse momentum contributed by each parton in the Erlang distribution and the string tension between partons in the Schwinger mechanism are obtained,and the related excitation functions are studied.It is found that a soft point in the equation of state appears at 7.7 GeV according to the excitation function of string tension based on the transverse momentum spectra of W hyperons.This soft point is very close to 8.8 GeV obtained from the method of squared speed-of-sound and in agreement to 4-9 GeV predicted by other methods.Meanwhile,the limit minimum distance between the partons is obtained to be 0.03 to 0.06 fm which is just a few percent of nucleon size.This renders that nucleons penetrate through each other totally in the collisions at the LHC.