Energy And Centrality Dependence Of P_T Spectra For Identified Hadrons In Au+Au And Cu+Cu Collisions At RHIC

The main purpose of relativistic heavy ion collisions(RHIC)is to obtain the information about the existence and properties of the hot and dense partonic matter,i.e.Quark-Gluon Plasma(QGP).Many experiments at RHIC have revealed many new properties of the final hadrons,which suggest that there might exist QGP in nucleus-nucleus collisions at high energy. Because of the confinement effect of partonic color,it is unavailable to detect the direct produced partons.Thus the information of the QGP properties has to be obtained from the character of the final hadronic state with phenomenological hadronization mechanism.The collectivity is an important feature of the hot and dense medium in high energy nucleus-nucleus collisions.The expansion evolution of the hot and dense quark matter may be the sequence of the large pressure of the bulk deconfined partonic matter in nucleus-nucleus collisions at RHIC.The collective expansion of the hot and dense quark matter is embodied in the final state hadrons,e.g.the collectivity of hadron pT spectra and hadron elliptic flow.The volume size of the strong-coupling hot and dense quark matter may be different in different collision centralities and energies,which may cause the different collectivity.In this work we apply the quark combination model to study systematically the dependence of collision centrality,collision system size and collision energy for the hot and dense quark matter.The work contains two aspects as follows:(â… )The centrality dependence and collision system size dependence of the hadron pT spectra are studied.Considering the variation of the hot and dense quark matter transverse collective flow in different centralities,the centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at(S_NN)^1/2=200 GeV is systematically studied in a quark combination model.The pT spectra ofÏ€^±,K^±,p(?)∧(?),(?)(?)andΩin different centrality bins and the nuclear modification factors(R_CP)for these hadrons are calculated.The centrality dependence of the average collective transverse velocity <β(r)> for the hot and dense quark matter is obtained in Au+Au collisions,and it is applied to a relative smaller Cu+Cu collision system.The centrality dependence of pT spectra and the R_CPforÏ€⁰,K_s⁰,and A in Cu+Cu collisions at(S_NN)^1/2=200 GeV are well described.The results show that <β(r)>is only a function of the number of participants N_partand it is independent of the collision system.(â…¡)We also study the energy dependence of hadron pT spectra at(S_NN)^1/2=130,62.4GeV respectively.With the quark combination model,we compute the hadron pT spectra,p/Ï€. K/Ï€and the R_CPfor hadrons and get the energy dependence of quark transverse collective flow.The results show that the hot and dense quark matter collective transverse velocity <β_r>is insensitive to the collision energy at 62.4—200 AGeV.