| Quantum chromodynamics(QCD)is the gauge theory describing the interactions between quarks and gluons,the building block of the ordinary nuclear matter.The non-abelian feature of QCD leads to the asymptotic free of the coupling constant.At low energy scale,the coupling constant becomes large and the method of perturbative expansion is invalid.Hadronization,the process of the formation of hadrons out of final state quarks and gluons,is a typical non-perturbative QCD process.Due to difficulty of non-perturbative QCD,the hadronization process is at present only simulated by the phenomenological models.The deep insights into the hadronization are mainly motivated by the rich data of high energy reactions.Quark(re-)combination model is one of phenomenological models for the hadronization.This model is proposed in early 1980s and is successfully applied to explain the data of e+e-,pp reactions at collision energies about dozens of GeV in early years.Recently,this model is extensively applied in relativistic heavy ion collisions to describe the production of soft hadrons.In ultra-relativistic heavy ion collisions,a new state of the matter in QCD,Quark-Gluon plasma(QGP),is formed in early collision stage.Quarks and gluons in QGP are deconfined.The QGP matter created in relativistic heavy ion collisions has the large volume(larger than 103fm3)and the relatively long lifetime ?10fm/c.The hadronization of QGP can be naturally described by the quark combination mechanism.At QGP hadronization,a quark and an antiquark neighboring in phase space combine into a meson and three neighboring(anti)quarks combine into a(anti)baryon.Observations at Relativistic Heavy-ion Collider(RHIC)such as the constituent quark number scaling of the hadronic elliptic flow(v2)and the enhanced baryon to meson ratios at intermediate transverse momentum(pT)clearly show that quark combination is an effective mechanism for QGP hadronization.Large Hadron Collider(LHC)pushes the center of mass energy per colliding nucleon up to TeV,which provides a new facility for the hadronization study.On the one hand,the QGP matter created in Pb-Pb collisions has larger volume and longer lifetime,leading to the further data of QGP hadronization.On the other hand,the small parton systems created in p-Pb and pp collisions show new features of the hadron production.For example,the enhancement of strangeness,ridge behavior and enhanced baryon to meson ratios are measured in high multiplicity events of p-Pb and pp collisions,which suggests the new hadronization mechanism other than the traditional fragmentation is needed at LHC.In the framework of quark combination mechanism,this thesis provides the new study of the soft hadron production at LHC energy both in large collision systems i.e.Pb-Pb collisions and in "small" collision systems i.e.p-Pb and pp collisions.In Pb-Pb collisions,the dynamical multiplicity fluctuations and correlations of identified hadrons are studied and compared with the ALICE data.In p-Pb and pp collisions,together with the study of yields and momentum distributions of light-flavor hadrons,the production of single-charm hadrons is studied in the equal velocity combination approximation and compared with the ALICE and LHCb data.The main contents of thesis are as follows:(1)Multiplicity fluctuation and correlation of mesons and baryons in ultra-relativistic heavy-ion collisions at the LHC.Based on the statistical method of free quark combination,we derive the two-hadron multiplicity correlations,including baryon-baryon and meson-meson as well as meson-baryon correlations,and take the effects of quark number fluctuation at hadronization into account by a Taylor expansion method.The dynamical sources of the fluctuations and/or correlations of the hadron production are discussed in QCM.When a quark hadronizes,it can come into either a baryon or a meson,which leads to the multiplicity fluctuations of global baryon and meson;in the same way,it can come into either a specific baryon(e.g.,a proton for a u quark hadronization)or another specific baryon(e.g.,a ?+),which leads to the multiplicity fluctuations of the proton and ?+ and also an anticorrelation between two baryons.In addition,correlations and fluctuations of quarks and antiquarks will pass to hadrons after hadronization.After including the decay contributions,we calculate the dynamical fluctuation observable vdyn for K?,p? and Kp pairs and compare results obtained with data from Pb-Pb collisions at(?)= 2.76TeV and simulations from the HIJING and AMPT event generators,we find that the quark combination can reproduce the basic behavior of vdyn and hadronic re-scattering effects are not negligible.(2)The production of single-charm hadrons in p-Pb collisions at(?)=5.02TeV and pp collisions at(?)= 7TeV.If QGP-like medium is created in p-Pb and pp collisions at extremely high collision energies,charm quarks that move in the medium can hadronize by capturing the co-moving light quark(s)or anti-quark(s)to form the charm hadrons.In this paper,using light quark pT spectra extracted from the experimental data of light-flavor hadrons and a charm quark pT spectrum that is consistent with perturbative QCD calculations,the central-rapidity data of pT spectra and the spectrum ratios for D mesons in the low pT range(pT ? 7GeV/c)in minimum-bias p-Pb collisions at(?)=5.02TeV and pp collisions at(?)=7TeV are well described by quark combination mechanism in equal-velocity combination approximation.The ?c+/D0 ratio in quark combination mechanism exhibits the typical"increase-peak-decrease" behavior as the function of pT,and the shape of the ratio for pT ?3GeV/c is in agreement with the preliminary data of ALICE collaboration in central rapidity region-0.96<y<0.04 and those of LHCb collaboration in forward rapidity region 1.5<y<4.0.The global production of single-charm baryons is quantified using the preliminary data and the possible enhancement is discussed.The pT spectra of(?)c0,?c0 in minimum-bias events and those of single-charm hadrons in high-multiplicity event classes are predicted. |
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