Measurements Of Open Charm Hadron Production And Non-prompt D~0 Elliptic Flow With The ALICE At The LHC

The human dream will not stop!With the development of science and technology and human cognitive level,exploration of the origin of human beings and the composition of the world has given rise to many different disciplines.The theory of the Big Bang indicates that the universe was born from a singularity explosion,and in the early stages of the explosion（0.1 fm-10 fm）,a new form of matter is formed:quark-gluon plasma（QGP）.Therefore,studying this substance helps us to understand the origin and formation of the universe.However,there has always been a question that has perplexed humanity:how to produce this high-temperature and high-density substance with strong interactions in the laboratory?In the 1970s,Dr.Lee Tsung-Dao proposed the idea of colliding heavy ions approaching the speed of light to study quark-gluon plasma.Based on this great idea,heavy ion collision experiments began to rise!The most famous ones include the Relativistic Heavy Ion Collider（RHIC）at Brookhaven National Laboratory（BNL）in the United States with the Solenoidal Tracker at RHIC（STAR）and the Large Hadron Collider（LHC）at the European Organization for Nuclear Research（CERN）with a large heavy ion experiment（ALICE）.The subject of this thesis is the ALICE experiment at the LHC,aiming to explore the properties of quark-gluon plasma by analyzing the experimental data from ALICE Run2.Due to the complex and fleeting evolution process of heavy-ion collisions,we can only rely on reconstructing and analyzing the hadron information at the collision endpoint to infer the properties of QGP.These hadron information can be classified into two types of probes:soft probes and hard probes.Soft probes include particle anisotropic flow,particle yield ratios,and so on,while hard probes include jets,heavy-flavor hadrons transverse momentum（_T）spectrum,and high_Tparticle spectra.Among them,heavy-flavor hadrons refer to hadrons carrying heavy-flavor quarks charm and beauty,which are considered as ideal probes for studying QGP because they mainly originate from the hard scattering process in the early stage of collision and undergo the entire collision system evolution process.Experimentally,the mechanism of hadronization,transport properties of QGP,and energy loss effect of partons in the QGP medium are mainly studied by analyzing the yield ratios,anisotropic flow,and nuclear modification factor of heavy-flavor hadrons.The currently observed experimental phenomena are not sufficient to prove the existence of quark-gluon plasma（QGP）in small systems,such as proton-proton and proton-nucleus collisions.Typically,experimental measurements in small systems can be used to test perturbative quantum chromodynamics（p QCD）and serve as a baseline for heavy-ion collision experiments.The production of heavy-flavored hadrons can usually be described by factorization theory based on p QCD.In factorization theory,the production of heavy-flavored hadrons is the convolution of three parts:the parton distribution functions of the incident protons,the cross-section of hard scattering between partons and heavy quarks,and the fragmentation function that describes the fragmentation of heavy quarks into heavy-flavored hadrons.Among them,the fragmentation function and the parton distribution functions of the incident protons are non-perturbative processes and can only be constrained by experimental measurements,while the hard scattering cross-section can be calculated by perturbative QCD.It is worth mentioning that the quark fragmentation function has long been considered universal,meaning that this process does not depend on the collision system and energy.However,despite the successful description of the charmo-nium production at the LHC energy region by the next-to-leading order perturbative calculation of the fragmentation function extracted from e⁺e^-and ep collision experiments,the production of theΛ_c⁺/D⁰baryon measured in proton-proton（pp）collisions at center-of-mass energies of 5.02 and 7 Te V at the ALICE experiment is significantly underestimated by the PYTHIA 8 calculation,which tuned the frag-mentation function from the e⁺e^-and ep collision experiments.Similar phenomena have also been observed in the proton-lead collisions at the central rapidity region of ALICE and the forward rapidity region of LHCb.Other heavy-flavored hadrons such asΞ_c^+,0/D⁰measured recently in pp collisions also confirmed that the fragmentation function is not universal for the collision system.It is worth mention-ing that the ALICE experiment used the minimum bias events,with the charged particle multiplicity being the average of the entire event.Measurement of theΛ_c⁺/D⁰yield ratio as a function as charged multiplicity can help us further understand the non-universal phenomena of fragmentation functions and the formation mechanism of open baryons in more detail,which will also better constrain the theoretical models.In addition,there has been a lack of measurement for bottom quarks in the central rapidity and low transverse momentum region in current experiments.The ALICE collaboration indirectly studies the properties of bottom quarks by measuring the decay products of bottom hadrons,such as electrons and muons from bottom quark decays,as well as non-prompt D mesons and quarkonia.In proton-proton collisions,studying the multiplicity of charged particles produced with bottom hadrons can help improve hadronization models.However,in heavy-ion collisions,it remains an experimental question whether bottom quarks with their larger mass are thermalized in the quark-gluon plasma（QGP）.Recently,the ALICE collaboration observed a significant positive elliptic flow of electrons from bottom hadron de-cays,indicating that bottom quarks could also participate in the thermalization process.However,the transverse momentum of these electrons only reflects the collective behavior of high transverse momen-tum bottom hadrons and cannot fully reflect the thermalization behavior of bottom quarks.Based on the current detector spatial resolution and luminosity,measuring the elliptic flow of non-prompt D mesons can better study the interaction between bottom quarks and the QGP.This thesis aims to study the hadronization mechanisms of heavy quarks and their interaction with the quark-gluon plasma（QGP）by measuring the production yields and elliptic flow of charmed hadrons and non-prompt D⁰mesons in the ALICE experiment at the LHC energy region.For the hadronization mechanisms of heavy quarks,the dependence of the promptΛ_c⁺production on the charged particle mul-tiplicity and the proportion of non-prompt D⁰mesons as a function of the charged particle multiplicity,as well as the non-prompt D⁰meson yield,were measured using proton-proton collision data collected from 2016 to 2018 at a center-of-mass energy of 13 Te V（about 1800 million events）.For the study of the interaction between bottom quarks and QGP,the elliptic flow of non-prompt D⁰mesons in non-central collisions was measured using lead-lead collision data collected in 2018 at a center-of-mass energy of 5.02 TeV.