Qgp In Relativistic Heavy Ion Collisions Evolution Of The Hadron,

The question whether the deconfined hot and dense quark matter—quark gluon plasma (QGP) has been produced in heavy ion collisions, the properties and the hadronization of QGP have attracted more and more attentions. The running of Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Lab provides opportunities to investigate these questions. The observables present many new features of final state hadrons and imply that QGP has probably been created. Abundant researches show that the quark combination, alias recombination or coalescence, is more preferable than the parton fragmentation in describing the hadronization of the hot and dense quark matter produced in relativistic heavy ion collisions. The building blocks of the quark combination mechanism(QCM) are the constituent quarks and antiquarks of various flavors (u, d, s etc) with momentum distributions. QCM assumes that when the hot quark matter cool down to the temperature of confinement phase transition Tc the system exhibits effective constituent quark degrees of freedom and gluon's dynamical degree of freedom is suppressed (or dynamical massive gluons have split into the quarks and antiquarks). The calculated results of Lattice QCD and its further analysis provide some support of this constituent quark picture just before hadronization.The whole process of the relativistic heavy ion collisions including the follows:formation of QGP, evolution, hadronization and rescattering. The properties of the final state hadrons are related with the evolution and the following hadronization of QGP, even with the interaction of hadrons. In the entire collision evolution process, constituent quarks (and their hadronization) are important link between (unobservable directly) partonic phase and (observed) hadronic phase. The (kinematic) properties of constituent quarks at hadronization, e.g. momentum spectra and collective flow, are the results of early evolution of hot and dense quark matter; meanwhile after hadronization they finally turn into those of hadrons observed experimentally. From these constituent quarks, explicit in QCM, one can obtain lots of information on the properties of the hot and dense quark matter produced in heavy ion collisions, e.g. strangeness and sound velocity.How to get the information of constituent quarks at hadronization? One economical way, as did in most references of combination-like models, is fitting directly from the data of the final-state hadrons, e.g. fitting light quark spectrum from pion and strange quarks from kaon. It is enough for the study of quark combination mechanism itself. However, this pure extraction can not establish the intrinsic association between quark spectra at hadronization and the early stage evolution of hot and dense quark matter, which stops us to gain more insights into the hot and dense quark matter from quark distributions. In this paper, we apply relativistic hydrodynamics to describe the evolution of hot and dense quark matter before hadronization. As the energy density of the fluid cell drops to the point of confinement phase transition, we stop the evolution and can obtain the quark distributions at hadronization. The subsequent hadronization is simulated by a quark combination model which incorporates also the following resonance decay. In the way of "hydrodynamics+combination", we can relate the hydrodynamic evolution of the hot and dense quark matter to hadron observables by the explicit quark distributions at hadronization. Various evolution information of the hot and dense quark matter can be obtained quantitatively and intrinsic properties of the matter can be traced back from the hadron data. Presently we focus on the transverse production of hadrons at midrapidity in heavy ion collisions. The work contains two aspects as follows:(Ⅰ) We systematically study the properties of the hot and dense quark matter produced in relativistic heavy ion collisions. In Au+Au and Cu+Cu collisions, through hydrodynamic evolution we obtain the properties of the hot and dense quark matter, such as:the time and energy dependence of energy density and asymmetry and the system size dependence of the evolution time, the averaged collective transverse velocity, and the transverse momentum distributions of the constituent quarks and antiquarks of various flavors (u, d, s).(Ⅱ) We systematically study the transverse momentum spectra for various hadrons. With the phase-space information of constituent quarks and antiquarks obtained by hydrodynamic evolution of the hot and dense quark matter, we calculate the transverse momentum spectra ofπ±,p(p),Ks0 and A at different centralities and different energies in Au+Au and Cu+Cu collision systems via the quark combination model. The results only including thermal quarks agree well with the data at low pT regions. It shows that our method can describe the evolution of hot and dense matter and its hadronization, and this further suggests that the properties of hot dense matter is reliable and the quark combination model is the universal hadronization mechanism. Then we predicted the transverse momentum spectrum of final hadrons at LHC in Pb+Pb collisions.