Charmed Baryon(?)_c~0 Production In Pp Collisions At(?)=5.02 TeV With ALICE

Shortly after the Big Bang our universe was in an extremely hot dense state.Nearly 14 billion years ago it is started expanding and cooling down and eventually evolves to its current form.During the early phases of its evolution,there was a phase transition where quarks and gluons turned from deconfined matter into confined states creating hadrons as protons and neu-trons.The deconfined state with free quarks and gluons is called the Quark-Gluon Plasma(QGP).It is characterized in terms of its high temperature T and high baryo-chemical ?B.The QGP state ended about ten microseconds after Big Bang when the temperature of the system cooled down below the critical temperature Tc.Afterwards the quarks and gluons formed a new state which is called the Hadronic phase.In order to unravel mysteries of universe high energy particle acceler-ators aim to recreate QGP under controlled laboratory conditions.High temperature and high energy densities axe required,which can be realized in ultra-relativistic heavy-ion collisions at the Large Hadron Collider(LHC).More specifically,A Large Ion Heavy Collider(ALICE)at the LHC is focus-ing on heavy-ion collisions to study strongly-interacting matter.The ALICE experiment explores the phase transition of QGP,its interaction with hard probes such as highly energetic particles and jets which carry information about the QGP.The interaction between quarks and gluons is one of the four fundamental forces in the Standard Model of particle physics.It is described by the theory of quantum chromodynamics(QCD).There are many areas of research in the field of high-energy heavy ion collisions.This thesis is focused on heavy flavor hadron production.Heavy quarks(charm quarks and bottom quarks)are expected to experience the whole evolution of the medium created in heavy-ion collisions.They strongly interact with medium and their large mass(mc0?1.25 GeV,mg0?4.5 GeV)sets a distinct perturbative scale.Due to their creation in a hard-scattering event they carry important information about medium and how it interacts with hard probes.Heavy flavor quarks/hadrons can be created in different collision systems such as pp,p-Pb,and Pb-Pb.The different collision sys-tems probe different aspects of heavy flavor physics in order to understand their production and evolution after the hard-scattering event.For exam?ple,measurements of the production of heavy-flavor hadrons in pp collisions are important to improve our understanding in terms of perturbative QCD which aims at describing both the production and hadronization of heavy flavor quarks.Furthermore,measurements of pp collisions provide the refer-ence for p-Pb and Pb-Pb collisions.This thesis 1s focused on studies of(?)c0 prod1ction in its semi-leptonic decay channel((?)c0?e+(?)-ve)in pp collisions.The data sample used in this thesis was recorded at(?)=5.02 TeV in pp collisions with the ALICE detector in 2017.The absolute branching ratio(BR)of the(?)c0 via its semi-leptonic decay channel((?)c0?e+(?)-ve)is currently unknown.Therefore,the final result of this thesis shows the pT-differential production cross section of(?)c0 multiplied by its branching ratio.The thesis is organized as follows.In Chapter 1,the general physics con-cepts are presented related to the Standard Model of particle physics and ultra-relativistic heavy-ion collisions.The LHC and ALICE setup are briefly described in Chapter 2 including the three main sub-detectors of ALICE used in this analysis.Chapter 3 contains a detailed description of the analy-sis strategy:event selection,candidate selection,signal extraction,unfolding techniques,reconstruction efficiency correction,and also corresponding sys-tematic studies.Chapter 4 shows the final result of the c0 production cross section.A comparison of the results obtained in this thesis at 5.02 TeV with the published results at 7 TeV is shown.Moreover,the ratio of the pT-dif-ferential cross section of(?)c0 and the measured production cross section of D0 mesons as function of pT is also presented,which is also compared with the published results at 7 TeV.Lastly,the measured transverse momentum dependence of the BR(?)c0/D0 ratio is compared with theoretical predictions from the PYTHIA 8 Monte Carlo event generator.The result shows a strong energy dependence of the production cross section of the(?)c0:higher energy,higher production cross section of(?)c0.Ratio BR*(?)c0/D0 is fully compatible with the published result at 7 TeV.The theoretical predictions from the Monte Carlo event generator PYTHIA 8 underestimate the measured ratio significantly.