Charged Hadron-V~0 Correlation In Pp Collisions At (?)=5.02 TeV With ALICE

Einstein once said:"Asking a question is much more important than solving it." Curiosity is not only the key to open the door of innovation,but also is the motivation for development.Some people cannot help asking,what is the smallest structure(basic unit)of matter?What did the early universe looks like?Nowadays,the Standard Model(SM)has become a well-tested theory in physics,which is based on the principle of gauge invariance.Quantum Chromodynamics(QCD)predicts that a phase transition can happen,where confined matter-hadronic state composed of protons and neutrons will be converted to a deconfined state called Quark Gluon Plasma(QGP),when the system reaches extremely high energy density and high temperature.QGP existed in the early universe and in the dense and collapsed stars,such as neutron stars.Therefore,studying QGP is one of great significance to the exploration of the internal structure of matter and the exploration of the early universe.To further study the properties of QGP,physicists have built a series of large colliders such as SPS,RHIC,LHC,etc.,expecting to generate QGP through high energy heavy-ion collisions.Because the process of collision and evolution cannot be directly observed,it is only possible to judge whether QGP is formed by measuring the information of the final products.The Large Hadron Collider(LHC)at the European Nuclear Research Center(CERN)is currently the world's largest collider.Among them,ALICE experiment detector mainly studies strong interactions under extreme energy density and also search for QGP signal,and then the strangeness enhancement has been considered as one of the earliest proposed QGP probe signal.ALICE experimental research results show that the effects of strangeness en-hancement can be observed in proton-proton(pp),proton-lead(p-Pb)and lead-lead(Pb-Pb)collisions;A new result about ?/KS0 having enhancement at intermediate transverse momentum(PT)interval is observed in small systems;Another result also show that the production of strange particles is dependent of multiplicity in high multiplicity pp collision,and the yield of different strange particles is arranged from high to low according to their mass ordering.Usually,the enhancement explained by a more dominant contribution from coalescence in comparison to fragmentation in a vacuum.Different hadronization mechanisms are related to each of these two kinematic regions:the yields in the near-and away-side peaks are usually associated with fragmentation;while the yields in the bulk regions are usually associated with soft processes such as coalescence.The interaction between Underlying event(UE)-dominated bulk region and jet-dominated hard(jet)processes may explain the s-trangeness enhancement and baryon-to-meson ratio enhancement effects observed in small systems.Therefore,this study is expected to provide new insights on the ori-gin of this enhancement by calculating the contribution of different dynamic regions(bulk and jet regions)to the enhancement effect of baryon-to-meson ratio(such as?/KS0)in the pp collision system.At the same time,this study can also provide a hint whether the baryon-to-meson enhancement has contribution from the modification of the parton fragmentation in the medium or it is only related to the hadronization mechanism(s)in the bulk.To explore the origin of the baryon-to-meson ratio enhancement effect in pp col-lisions,In this analysis,the data recorded at(?)=5.02 TeV in pp collisions with the ALICE detector in 2017 was analyzed by using the two-hadron correlation tech-nique to evaluate the baryon-to-meson ratio(?/KS0).The charged hadrons with high transverse momentum(5<pT<15GeV/c)are used as trigger particles to associate with the strange particles KS0 and ?(1<pT<7GeV/c).The advantage of this method is that the ratios of ?/KS0 in different regions can be obtained by separat-ing the hadrons produced in the collision bulk from those produced in association with a high pT charged partice.To further explore whether the baryon-meson ratio enhancement effect attributed to soft process or hard process,so as to evaluate the effects of different hadronization mechanisms on the baryon-to-meson ratio enhance-ment effect,providing new insights on the hadronization process.The result of this thesis can provide a reference for p-Pb and Pb-Pb collision systems.This thesis begins with a short theoretical introduction to the SM of elementary particles in modern particle physics,the QGP,the physical meaning of high-energy heavy ion collisions.The current status and research motivation of the baryon to meson enhancement is also shown.Chapter 2 gives a detailed description of the ALICE experimental device and the 2 sub-detectors mainly involved in this analysis.Chapter 3 describes the basic process of the entire analysis work,including event selection,trigger particle selection,associated particle selection,charged hadrons and V0 particles correlation,reconstruction efficiency correction,acceptance correction,feed-down correction and other parts.It also uses two feed-down methods to correct the yield of primary A particles.Chapter 4 shows the corrected ?,KS0 per trigger yields in the bulk and jet region,respectively,and the final results about ?/KS0 ratio distribution.The results show that with the increase of pT in the pp collision system,the ratio of ?/KS0 will be have a peak at the intermediate transverse momentum pT=3 GeV/c.In the entire pT interval,the ratio of ?/KS0 in the bulk region is generally higher than in the jet region.The maximum value of the ?/KS0 ratio in the bulk region is 0.52,while the maximum value in the jet region is approximately 0.29.It can be inferred that the enhancement effect of the baryon-to-meson ratio(?/KS0)in pp collisions at(?)=5.02 TeV mainly comes from the influence of the soft process in the bulk region.The chapter 5 presents a summary of the entire analysis work and the prospect of future work.