Prompt And Non-prompt D~0-meson Production In Au+Au Collisions At(?)=200 GeV At RHIC

Quantum ChromoDynamics(QCD)is a theory of describing the strong interaction between quarks and gluons.One property of QCD is the phenomenon that quarks and gluons are confined inside hadrons in normal conditions,which is called color confine-ment.However,while the energy scale increases and the corresponding length scale decreases,the interaction between quarks and gluons will get asymptotically weaker.Lattice QCD calculations predict a new state of matter in which quarks and gluons are de-confined at extremely high temperature and high density.This new state of matter is called Quark-Gluon Plasma(QGP).The QGP state is believed to exist in the uni-verse at a few milliseconds after the Big Bang.To create the QGP experimentally,the high energy heavy-ion collisions has been a unique tool.The Relativistic Heavy Ion Collider(RHIC),is one of the two current operating heavy-ion colliders in the world,which provides an excellent opportunity to search for the QGP and study its properties at laboratory.Heavy quarks(c,b),are considered as an ideal probe to study the properties of the QGP.Due to their large masses,thermal production of cc/bb pairs are suppressed and they are predominantly produced through initial hard scatterings during high energy heavy-ion collisions.The total yields of charm and bottom quarks are calculable with the perturbative QCD and connected directly to the initial state.Heavy quarks experi-ence the entire evolution of the hot and dense medium(QGP).While they traverse the medium,heavy quarks will lose energy through plenty of elastic collision and medium-induced radiation.Particularly,theory predicts a mass dependence of the energy loss:?Eg>?Eu,d,s>?Ec>?Eb.Systematic investigations of charm and bottom hadron production in heavy-ion collisions are crucial for understanding the parton energy loss mechanism in the medium.The propagation of heavy quarks inside the QGP can be treated as;"Brownian" motion because both the temperature of the medium and the in-teraction strength between the heavy quarks and the medium are much smaller than the masses of heavy quarks.The equation of motion of heavy quarks,usually treated as a Fokker-Planck equation,can be solved by a stochastic Langevin approach and charac-terized by a spacial diffusion coefficient Ds.The low-pr measurements of heavy quarks can be used to constrain this diffusion coefficient.In addition,the open charm and bot-tom hadrons may be produced in a "thermal" fashion when charm and bottom quarks are surrounded by the medium.It may lead to significantly modified abundances of the open charm and bottom hadrons.Systematic study of the production of all kinds of the open charm and bottom hadrons will help understand the hadronization mechanism in the medium.There have been great achievements in heavy flavor measurements in the past few years with new instruments and large datasets collected at RHIC and LHC.Recent re-sults show clear evidences that the nuclear modification factor of D0 mesons at high transverse momenta as well as their elliptic flow at low transverse momenta are similar to those of light flavor hadrons,which indicates that charm quarks may be thermalized in the QGP medium at top RHIC and LHC energies.The next phase of heavy quark program will be focusing on the precise measurements of open bottom and heavy quark correlations.We have observed the evidences of mass hierarchy of parton energy loss.A detailed investigation on open bottom production in heavy-ion collisions will be nec-essary to evaluate quantitatively the roles between radiative energy loss vs.collisional energy loss.Open bottom production will also offer the cleanest way to measure the heavy quark diffusion coefficient due to its much larger quark mass compared to the charm quark.Total bottom yield will further help a precision interpretation of Y results measured in heavy-ion collisions.In this thesis,We report on the precise measurement of inclusive D0 production in Au+Au collisions at(?)=200 GeV at STAR.Using the data collected by STAR with the new installed Heavy Flavor Tracker(HFT)in 2014,D0 can be topologically reconstructed through the hadronic decay channel D0?K-?+.The efficiency cor-rected spectrum and the nuclear modification factor of D0 down to pT=0 are presented.Combined with the spectrum of other charmed hadrons(?c+ D+and Ds+)measured at STAR,the total cross-section of cc per nucleon-nucleon collision at mid-rapidity in Au+Au collisions at(?)=200 GeV is calculated and consistent with that measured in p+p collisions at(?)=200 GeV at STAR.We also analyze the data in 2011(with-out HFT),2014(without HFT)and 2016(with HFT)to cross-check the D0 spectrum obtained in 2014(with HFT),and get consistent results.The first measurement of non-prompt D0 production in Au+Au collisions at(?)200 GeV at STAR is reported.Since the bottom hadron production rates at RHIC colli-sion energies and branching ratios of hadronic decay channels are small,we cannot use the standard method of invariant mass reconstruction as inclusive D0 for bottom hadron measurements.However,due to the excellent pointing resolution in both the beam di-rection and the transverse plane provided by the HFT,we can extract the non-prompt D0 contribution(from B-decay)to the inclusive D0 yield through the distribution of the three-dimensional distance of closest approach(DCA)of D0 to the primary vertex.Since the lifetimes of bottom hadrons are longer than D0 mesons,the DCA distribution of the non-prompt D0 should be wider than the prompt D0.Combining the HFT data in 2014 and 2016,we present the centrality and transverse momentum dependence of the non-prompt D0 fraction as well as its nuclear modification factor in Au+Au collisions at(?)=200 GeV.The nuclear modification factor of the non-prompt D0 is compared with that of the inclusive D0.A hint of less suppression for non-prompt D0 is observed,which is consistent with the mass dependence of parton energy loss in the medium.In addition,we estimate the performance of measuring D0-meson and B-meson pro-duction in Au+Au collisions at(?)?200 GeV for the sPHENIX experiment with the Monolithic Active Pixel Sensor Vertex Detector(MVTX).Based on a hybrid fast Monte Carlo(MC)method with full GEANT+tracking input,the statistical uncertainties of the nuclear modification factor and the elliptic flow of both the inclusive D0 and the non-prompt D0 are projected within 0<pT<10 GeV/c.Besides,we estimate the full reconstruction for B+-meson through the hadronic decay channel B+?D0?+ The statistical uncertainties of total bb cross-section at mid-rapidity is also projected.