Research On Hadron Production In The Quark Combination Imag

Hadronization is the process of forming hadrons from final-state quarks and gluons crelated in high-energy reaction.Because of non-perturbation difficulty of quantum chromodynamics(QCD),it is hard to study the hadronization by direct QCD calculations and simulations from the first principles.At present,phenomenological models are developed as the main method of hadronization studies with the close interaction with high energy collision experiments.Since the Relativistic Heavy Ion Collider(RHIC)at Brookhaven National Laboratory and the Large Hadron Collider(LHC)at European Organization for Nuclear Research(CERN)were started,a series of novel phenomena related to hadronization have been discovered,such as the enhancement of the baryon-meson ratios(e.g.,large baryon-meson ratio of charm hadrons Λc/D)in the intermediate transverse momentum(pT)region,the constituent quark number scaling of the hadronic elliptic flow,the splitting of the nuclear correction factors for baryon and meson,and the fine structure of the strange hadron yields,etc.The transditional fragmentation mechanism can not explain these experimental phenomena while the quark combination mechanism can provide a natural explanation.Nearly two decades of theoretical and experimental research in relativistic heavy-ion collision physics have shown that a new state of matter,the unconfined quark gluon plasma(QGP),has been produced at both RHIC and LHC energies,and the quark combination mechanism is an effective hadronization mechanism of QGP.The hadronization models under quark combination scenario have successfully explained a series of properties of hadron production at both RHIC and LHC energies.However,because of non-perturbative difficulties quark combination dynamics still have many unclear issues.Fortunately,the continuously publication of new high-precision experimental data at LHC and RHIC provides an excellent opportunity and solid foundation for the deeper study of the hadronization mechanism.In this thesis,the production of the hadrons in the Pb+Pb collision at LHC energy and Au+Au collision at RHIC energy are studied by applying the quark combination model with the help of high-energy collsion experiments.Specifically,properties of the hadronc yield,the pT spectra,baryon-to-meson ratio,nuclear correction factor,and the anisotropic flow for the Au+Au collision at(?)=7.7-200 GeV are systematically studied.Furthermore,the correlation between the average transverse momentum of the hadrons in Pb+Pb collision at LHC energy and Au+Au collision at RHIC energy is studied.By a full comparison of the theoretical results with the experimental data,the mechanism of quark combination hadronization are systematically tested and a deeper understanding of the dynamic features of quark combination is obtained.On the other hand,taken hadronization as a key link between QGP at hadronization and final-state hadrons observed in experiments,some important information(cg.,hadronization temperatures,collective flows,strangeness,etc.)about QGP produced in the early stage of relativistic heavy-ion collisions are obtained and studied.The main research contents of this thesis are as follows:(1)Collision centrality and energy dependence of hadron production in Au+Au collision at RHIC energyAn equal-velocity quark combination model is applied in this thesis to systematically study the transverse momentum(pT)spectra of identified hadrons KS0,φ,Λ,Ξ-,Ω-,Λ,Ξ+,Ω+,p,p,π+ and π-at(?)=7.7,11.5,19.6,27,39,54.4 GeV in Au+Au collision at RHIC energy.The results indicate that the equal-velocity quark combination model can provide a globally consistent explanation on pT spectra of these hadrons,and the degree of coincidence does not exhibit an obvious dependence on collision energy.However,due to the limited number of experimental data points and the narrow transverse momentum region for the collision energy of 7.7 GeV,it is impossible to draw firm conclusions in comparing the model results with the experimental data.The dependence of the baryon meson ratio(Λ/KS0,Ω/φ)on the transverse momentum,collision centrality and collision energy are also well explained.The analytic relations between RCP of hadrons and those of quarks are derived,which are found to be able to naturally explain the species and pT dependence of RCP of those strange hadrons.This work has been published in Physical Review C,107,024909(2023).(2)Averaged transverse momentum correlations of hadrons in relativistic heavy-ion collisions at both RHIC and LHC energiesThe averaged transverse momentum(<pT>)of hadrons carries lots of informations about the collision process of heavy ions.By compiling and analyzing experimental data for(pT)of the proton,Λ,Ξ-,Ω-and φ at midrapidity in Au+Au collisions at(?)=200,39,27,19.6,11.5,7.7 GeV and in Pb+Pb collisions at(?)=2.76 TeV,it is found that these hadrons exhibit systematic correlations.How to understand these correlations?A quark combination model with equal-velocity combination approximation is used to derive analytic formulas of hadronic(pT).These analytical formulas can successfully explain the systematic correlations exhibited in<pT>data of pΛ,ΛΞ-,Ξ-φ-,and Ξ-φ pirs.They also successfully explain the regularity observed in<pT>of these hadrons as the function of(dNch/dy)/(0.5Npart)at midrapidity in central heavy-ion collisions at both Relativistic Heavy Ion Collider(RHIC)and Large Hadron Collider(LHC)energies.These results suggest that the constituent quark degrees of freedom and the equal velocity combination of these constituent quarks at hadronization play an important role in understanding<pT>correlations of baryons and φ meson in heavy-ion collisions at these RHIC and LHC energies.This work has been published in Physical Review C,106,034910(2022).(3)Anisotropic flows of hadrons in Au+Au collisions at RHIC energyAn equal-velocity quark combination model is used to systematically study the anisotropic flows v2,v3,and v4 of identified hadrons φ,Λ,Ξ-,Ω-,Λ,Ξ+,Ω+,p,and p at midrapidity(|y|<1.0)in Au+Au collisions at RHIC energy.Analytic relations between anisotropic flows v2,v3,v4,and v5 of hadrons and those of quarks are obtained,and are applied to Au+Au collisions at(?)=19.6,54.4,and 200 GeV to naturally explain the dependence of the v2,v3,and v4 of those hadrons on the transverse momentum,collision centrality and collision energy.Further investigation of the anisotropic flows of quarks,and find that there is a scaling relation vn,q(pT)～v2,q n/2(pT)between the anisotropic flows of quarks.This scaling relation is transferred to the hadrons via quarks combination at hadronization,which naturally gives the scaling behavior between hadronic anisotropic flows.