The Rapidity Dependence Of Hadron Production In RHIC

The study of hadronization mechanism is one of the most important projects in the field of high energy heavy ion collisions.The conversion of hot and dense quark matter into normal hadronic matter is a typical non-perturbation process,and there is no effective theory to describe this process at present.The most common used methods are either the "fragmentation function" parameterized from experimental data or the phenomenological hadronization model.The nucleus-nucleus collisions at RHIC energy produce an abundance of hot and dense quark matter of which the hadronization results provide an advantageous condition to study and examine the different hadronization mechanisms.Since the running of RHIC in 2000,the experiment collaborations have measured a series of hadronization-related new features,e.g.the high baryon-meson ratios in intermediate transverse momentum region and the quark-number-scaling of hadron elliptic flow.These new features can not be understood completely in the scheme of fragmentation picture,however it can be naturally described in quark combination picture.It is a suggestion of the validity for quark combination mechanism in describing the hadronization of hot and dense quark matter produced in collisions.Recently,many more detailed experimental data are measured by RHIC experiments. It provides a good opportunity to make a further study of quark combination hadronization mechanism in high energy heavy ion collisions.In the present paper,we make a study of two aspects of hadronization mechanism in relativistic heavy ion collisions.(â… )The influence of net-quarks on the yields and rapidity densities of hadron and antihadron. The data from RHIC show that the nucleus-nucleus collisions at RHIC energies are quite transparent compared to lower AGS and SPS energies.Most of the net-quarks after collisions are not fully stopped,still carry a fraction of initial collision energy and are located in forward rapidity region.Therefore the longitudinal evolution and distribution of net-quarks should be obviously different from that of newborn quarks.In this paper,distinguishing the rapidity distribution of net-quarks from that of newborn quarks,we use the quark combination model to make a detailed study of the influence of net-quarks on the yields and rapidity distributions of various hadrons in central Au+Au collisions at(S_NN)^1/2=200 GeV.It is found that while we distinguish the rapidity spectrum of net- quarks from that of newborn quarks,the yields and rapidity distributions of various hadrons and antihadrons can be naturally described.The difference of yields and rapidity densities between hadrons and antihadrons,and the rapidity dependence ofÏ€^-/Ï€⁺,K^-/K⁺ and(?)/p can all be coherently explained in the scheme of quark combination.The yields and rapidity spectra of K_S⁰, ∧((?)),∑+((?)^-),(?)((?)⁺)andΩ^-((?)⁺)in central Au+Au collisions at(S_NN)^1/2=200 GeV are predicted.(â…¡)The rapidity dependence of hadron P_T spectra.Recently,the property of hot and dense quark matter produced in collisions at forward rapidity region attracts more and more attentions.Can the QGP extend to forward rapidity? If it does,how much rapidity can it extend to? which observations can be used to effectively manifest the difference between the property of hot medium at high rapidity and that at midrapidity? Using the quark combination at all P_T,we calculate the transverse momentum spectra of identified hadrons at different rapidities y～0,1,η=2.2 and y≈3.2,and compare the results with the experimental data.It is found that quark combination mechanism may still play an important role at high transverse momentum up to 12 GeV/c.Using the same transverse momentum spectra for quarks,we calculate the transverse momentum spectra at various rapidities y～0,1,η=2.2 and y≈3.2.The results are in good agreement with the data except those for proton and antiproton at y≈3.2.