The Study Of Hadron Yield Correlation In High Energy Heavy Ion Collisions

The study of the hadronization mechanisms of high energy reactions is always an important but challenging issue in high energy physics. So far, researchers still in-vestigate indirectly the hadronization mechanisms of the deconfined partonic matter mainly by studying some hadronic observables sensitive to the hadronization mecha-nisms with phenomenological methods, since the Non-Perturbative Quantum Chromo-Dynamics (QCD) has difficulties in dealing with it directly. Hadron yield correlations, measured by the ratios of the average yields of different hadrons and the relationships of such yield ratios, are one kind of characteristic properties of hadronization mecha-nisms. They were therefore considered as good probes for the hadronization mechanism in e++e-annihilations and p+p, π+p reactions already in the1970s. Recently, many people extend the study of hadron yield correlations to high energy heavy ion collisions. As is well known, the quark combination mechanism is a powerful candidate for deal-ing with the hadronization of the partonic matter created at the early stage of heavy ion collisions. Testing the quark combination in heavy ion collisions is interesting be-cause whether the combination mechanism works might be considered as one of the signatures for the formation of the bulk color-deconfined quark matter system before the hadronization takes place. Besides, it can set lights to the search for the onset of deconfinement in nucleus-nucleus collisions and the further comprehension of the QCD phase diagram.Experimental data on hadron yield correlations are available from the BNL Rela-tivistic Heavy Ion Collider (RHIC), from relatively low energy collisions such as those obtained by NA49, NA61, and CBM Collaborations at the CERN Super Proton Syn-chrotron (SPS), and more recently from the very high energy reactions at the CERN Large Hadron Collider (LHC). So far, lots of experimental data at different collision en-ergies with different nuclei and in different kinematic regions have been accumulated. These data provide opportunities for different combination models to test the quark combination mechanism in heavy ion collisions.One can justify the quark combination mechanism by comparing the results calcu-lated by combination models with the experimental data. Different combination models, such as ALCOR model, quark (re-)combination or coalescence models have extensively studied hadron yield correlations and explained many observed interesting phenomena. However, different models use different assumptions and/or approximations. It is impor-tant to see whether, if so, to what extent, the theoretical results depend on the particular assumptions and/or approximations used in obtaining these results. For this purpose, we systematically investigate hadron yield correlations in the framework of the quark combination. We will start the study by considering the general case of the combination of quarks and antiquarks in a system from the basic ideas of the combination mecha-nism. We will make the study as independent of the particular models as possible but present the assumptions and/or approximations explicitly whenever necessary. We first deduce the general formalism of the yields of various hadrons and then systematically investigate different kinds of hadron yield correlations.The outline of the contents and conclusions of this thesis is as follows:(1) We deduce the general formalism of the yields of different hadrons in the frame-work of the quark combination. Adopting the factorization assumption, i.e., the assump-tion of the factorization of flavor and momentum dependences of quark combination functions (kernel functions) and the assumption of the flavor independence of the nor-malized quark joint momentum distributions, we analytically deduce the formulae of different directly produced light and strange hadron yields in the quark combination mechanism. Adding the decay contributions from resonances, the formulae of different final state hadron yields are obtained. Besides the total average yield of mesons (NM), the total average yield of baryons (NB) and that of antibaryons{NB), these hadron yields only depend on several familiar parameters:the ratio of the Jp=1-vector mesons to the Jp=0-pseudoscalar mesons of the same flavor composition RV/p, the ratio of the Jp=(1/2)+octet to the Jp=(3/2)+decuplet baryons of the same flavor composition Ro/d, the strangeness suppression factor for antiquarks A, and the effective strangeness suppression factor for quarks λq. Especially, when RV/P=3and Ro/D=2are taken, these hadron yields only depend on λ and λq, besides (NM),(NB) and (NR). If the influence of the net quarks can be ignored, we have λ=λq and the further simpler hadron yield formulae can be obtained.(II) With the above deduced hadron yield formulae, we further study different kinds of hadron yield correlations. Firstly, we consider ultra high energy collisions where the net quark influence can be ignored. In this case, λ=λq and many yield corre-lation results independent of any parameters or only depending on A or depending on λ and (NB)/(NM) are obtained and compared with the experimental data from LHC (?)s=2.76TeV Pb+Pb collisions. Then, including net quarks, we get the yield ratios between different baryons or antibaryons depending only on λ and λq, the yield ratios between baryons or antibaryons and mesons related with λ, λq and (NB)/(NM) and compare these results with the data from RHIC (?)s=200,130,62.4GeV Au+Au collisions and SPS Ebeam=158,80,40,30AGeV Pb+Pb collisions. Finally, we systematically study the baryon-antibaryon flavor correlations from three aspects since baryons and antibaryons suffer less decay contaminations from resonances and can probe the hadronization mechanism more clearly. One is the relationships between different species of antibaryon-to-baryon ratios and (NK-)/(NK+). In the quark com-bination, we get that different antibaryon-to-baryon ratios, e.g.,(Np)/(NP),(NA)/(NA),(N(?)+)/(N(?)-) and (NΩ+)/(NΩ-) relate with (NK-)/(NK+) by λ, but not sensitive to the values of λ. Two is several interesting regularities independent of any parame-ters. We define the following hadron yield correlation quantities In the quark combination, A=B=1and d∧≡=dpΩ. In addition, we discuss the mixed ratios and find that All these results in the QCM are compared with the available data from different experimental collabo-rations at LHC, RHIC, SPS and AGS. Three is the baryon-antibaryon flavor correlation factors. We provide predictions in cases of ignoring and considering the global flavor compensation of quarks and antiquarks, respectively, for comparison with the future measurements.The study shows that the results of the yield correlations of different light and strange hadrons in the QCM are consistent with the data from LHC (?)s=2.76TeV, RHIC (?)s=200,130,62.4,39;19.6,11.5GeV and SPS Ebeam=158,80,40,30AGeV, which justifies the quark combination in heavy ion collisions at these energies; but they disagree with the data from RHIC (?)s=7.7GeV, SPS Ebeam=20AGeV and AGS Ebeam=14.6,11.7,8AGeV, and even deviate seriously from the AGS data, which indicates the invalidity of the quark combination at these low reaction energies.(Ⅲ) With a few data of charm hadrons in Pb+Pb collisions at LHC published by the ALICE Collaboration, we extend the quark combination to the charm sector and point out that the measurement of the yields of hadrons with single charm valence quark can provide important insights into charm quark hadronization mechanism and properties of the hot and dense matter produced in high energy reactions. We propose several types of yield ratios of hadrons with single charm valence quark to measure various properties of low PT charm quark hadronization. We argue that ratios of open charm mesons as the function of PT can serve as good probes for the dynamics of charm quark hadronization.All the results we obtained in this thesis show that with the assumption of the fac-torization, the yields of different light, strange and charm hadrons exhibit a series of simple and interesting relations. These relations are independent of particular combina-tion models, independent of precise forms of quark joint momentum distributions and quark combination functions and they are the general results of the quark combination. They are valid as long as the quark combination is at work and the factorization as-sumption is valid, so they can be used to test the validity of the quark combination. The experimental data at LHC, high RHIC and SPS energies agree well with these results obtained in the general quark combination mechanism, which shows the validity of the quark combination and further indicates the deconfined QGP has been produced in these collision energies. The data at low energies, i.e., at AGS energies, deviate from these results in the QCM. This suggests the invalidity of the quark combination and further indicates QGP has not been created in such low energy collisions.