Study Of The Heavy Quark Detection Via Hadronic And Dimuon Channels At LHC/ALICE And Jet Quenching Effect At QCD Medium

Some of fundamental questions of nature are to study the interaction of particles and its regular.According to the prediction of standard model(SM),quarks and leptons are the elementary particles existed in nature.Strongly interacting force between quarks is exchanged by a kind of gauge particle named gluon.Due to the color confinement,quarks and gluons are restrained in hadron.From the calculation of lattice Quantum Chromo-dynamics(LQCD) a deconfined phase transition from hadron to quark-gluon plasma(QGP) state will occur.Studying the properties of the QGP phase will directly test the prediction of LQCD and reveal the regular of the strong interaction.The deconfined phase is thought to have constituted the 1-μs-old Universe.Therefore the experimental detection of QGP signal can also help us to understand the history of the Universe.Nucleus-Nucleus(A-A) collisions are the unique tool available to investigate phase transition of QCD matter in laboratory.A lot of work has been devoting to the exploration of the matter in last 30 years.The Forthcoming Large Hadron Collider(LHC) will contribute to such study to increase the center-of-mass energy of a factor 30 and energy densities of a factor 1-10 with respect to RHIC.ALICE(A Large Ion Collider Experiment) is one of the four experiments at LHC.The goal of the ALICE aims at the study of nucleus-nucleus collisions at center-of-mass energy(for Pb208) of 5.5 TeV per nucleon-nucleon(N-N) pair,studying the chiral symmetry restoration and the deconfinment phase transition.The experimental data of Proton-proton(p-p) collisions with s1/s=14 TeV at LHC,which can be used as the baseline of A-A collision data in ALICE,will be obtained in the end of this year.This thesis mainly focus on the study of the performances of ALICE for the heavy flavor measurement via hadronic and dimuon channels at central barrel detector system(for D*± reconstruction) and forward muon spectrometer(for primary B and D hadrons production cross section measurement) respectively.After the introduction of Physics motivation to study deconfinement matter at LHC/ALICE in chapter 1,the heavy flavor physics at LHC energies will be presented in chapter 2.The previous experimental results for heavy flavor measurement at SPS and RHIC are shown in chapter 3.The structure and principle of the ALICE detectors which are used for simulation framework of our this study on experimental simulation, particle tracking reconstruction and data analysis are presented in Chapter 4.In chapter 5,the preliminary results of D*± reconstruction at ALICE central barrel will be described.The D*± mesons are reconstructed via the hadronic cascade process,D*+→D0πs D0→Kπ.Due to a cascade decay structure,which is different from 2-prong decay topology(D0→Kπ) and 3-prong decay topology(D±→Kππ), a new data structure is needed to analysis and storage it.After explaining the motivation and methods of D*± reconstruction,we introduce our improvement of the analysis framework of heavy quarks at ALICE central barrel in AliRoot,which is a software package used to data analysis at LHC/ALICE,for D*± reconstruction and analysis.Then we test the structure cut,PID cut and kinematics cuts for the D*± candidates finding in p-p collisions with s1/2=14 TeV,respectively.Our results show that all the cuts used in our work can improve the significance of D*± signal under the peak of the spectrum of MKππ-MKπ observably,and the main background comes from theπs candidate selections.We will focus on how to improve theπs tracking and selection efficiency at the next steps.The performance of the ALICE muon spectrometer for the measurement of the B and D hadron production cross section in p-p collisions at s1/2=14 TeV is introduced at chapter 6.We first assume theμ-μ+ come from the resonances(J/Ψ,γet.al.) and the uncorrelated background are subtracted perfectly.Then we fit the distribution of correlatedμ-μ+ come from charm and bottom respectively.According to the shaping functions of f(Mμ-μ+D) and f(Mμ-μ+B),which gotten from the fitting,the correlatedμ-μ+ can be separated well.And the production cross section of primary B and D hadrons are obtained by normalizing the number ofμ-μ+ from B and D hadrons by multiplying a MC factor FMC,respectively.After describing the fitting processes,we present how to get the value of FMC and the systematics errors from the FMC are estimated.The results indicate that the production cross section of B and D hadron can be reconstructed at very low pt range(pt≈2 GeV for B hadrons and pt≈3 GeV for D hadrons).The systematics errors are 15%for B hadrons and 20%for D hadrons.The measurement represent a crucial benchmark for pQCD calculations and are essential for the understanding of the corresponding results in Pb-Pb collisions.The heavy quark energy loss effect in QCD medium are studied at chapter 7. In this chapter two kinds of parallel calculations of heavy quark radiative energy loss scenarios(reaction operator approach and single hard approximation) are used to calculate the temperature dependence of the heavy quark energy loss in hot and density QCD medium at RHIC and LHC energies,respectively.The results show that due to the high incident energy of the partons,the temperature of the medium can be neglect especially at high parton energy region.And at high pt region the heavy quark radiation energy loss is not sensitive with the medium temperature.As only considering the radiation energy loss can not explain the non-photonic electron suppression successfully at RHIC,we further consider the collisional energy loss for the heavy parton in the QCD medium,and by adding this new energy loss mechanism, our results are well agreement with the experimental data.A short discussion about the surface emission is given at the end of this chapter.