Charmed Meson And Baryon Production In Au+Au Collisions At ?^SNN?^1/2=200 GeV At RHIC

A hot and dense form of matter is believed to be produced in Au+Au collisions at?^SNN?^1/2=200 GeV at the Relativistic Heavy-Ion Collider?RHIC?.To measure the properties of this new deconfined state of matter,the Quark-Gluon Plasma?QGP?,is one of the main goals of the heavy-ion collision experiments.Due to the large quark mass,charm quarks are dominantly produced in the early stage of the collision in hard scattering processes at RHIC.And they experience the whole evolution of the system,offer unique information for the study of hot and dense strongly-coupled QGP matter.Open heavy flavor hadrons have a very short decay length.Experimentally,heavy flavor hadron reconstruction is carried out through semi-leptonic decays or the hadronic decays both with their respective advantages and disadvantages.Electrons from semi-leptonic decays,referred to as non-photonic electrons?NPE?,have relatively high branching ratios and can be triggered by detectors.The interpreta-tion of the NPE measurements relies on good understanding of leptons from the various charmed and bottom decays contribution.Also,due to decay smearing the pT of their parent heavy flavor hadrons can come from a wide kinematic region.The hadronic channels allow to fully reconstruct the charmed hadrons and do not suffer from the complications in the semi-leptonic decays.However the measurement can be challenging due to large combinatorial backgrounds and lower branching ratios.This requires the detectors must be able to resolve differences on the order of tens of microns.The Heavy Flavor Tracker is an excellent dector in charged track projections for this propose.Heavy quarks nuclear modification factor?RAA?has been proposed as an important measurement to study the flavor dependence of partons energy loss in the medium,and eventually to help in extracting the medium transport,drag and diffusion coefficients.Measurements of heavy quarks v2 at low transverse momentum promise to quantify the degree of thermalization of the bulk matter.In particular,low and mid momentum heavy quarks could hadronize via recombination,this could affect the pT dependence of measured spectra and v2.At high pT the D meson v2 can constrain,together with the RAA,the path dependence of the in medium energy loss.The precise measurement of charm hadron production could be crucial for the total charm yield,and provide the baseline for charmonium suppression and coalescence.For example,if the charmonium states at low pT are created by coalescence of flowing charm and anti-charm from the medium,they will carry the original flow of these charm quarks.On the other hand,if charmonium states are produced promptly,they are lesslikely to flow.At RHIC,enhancements in the baryon-to-meson ratio for light hadrons and hadrons containing strange quarks have been observed in central heavy-ion collisions compared to those in p+p and peripheral heavy-ion collisions in the intermediate transverse mo-mentum?pT?range?2<pT<6 GeV/c?.This can be explained by the hadronization mechanism involving multi-parton coalescence.?c is the lightest charmed baryon with mass close to that of D0 meson,and has an extremely short life time?c??60?m?.Different models predict different magnitudes of enhancement in the Ac/D0 ratio de-pending on the degree to which charm quarks are thermalized in the medium and how the coalescence mechanism is implemented.From the experiment side,it would be nature to measure this baryon-to-meson ratio for heavy quarks.Also,since charm baryon decays produce less electrons than charm meson decays,an enhancement in Ac/D0 ratio will result in a suppression in the non-photonic electron yield in heavy-ion collisions.Measurement of Ac and Ds hadrons are important to determine the total charm yield at mid-rapdity.The baryon-to-meson enhancement can be explained by the coalescence hadroniza-tion through recombination of constituent quarks.Theoretical calculations for such an enhancement would be sensitive to how the coalescence mechanism is implemented and the degree to which charm quarks are thermalized in the medium.Therefore it is important to measure Ac and Ds charm hadron yields to better con-strain the total charm yield in heavy-ion collisions,and also crucial for distinguishing these models and shed lights on the charm quark hadronization in the hot and dense medium.So in these dissertation,I report the details of our first measurement of D0,D±and Ac production via their topological reconstruction using the Heavy Flavor Tracker?HFT?at STAR.We report the measurement of efficiency corrected spectrum for D0 and D± through the hadronic channels?D0?D0??K????± and D±?K????±?±?,the Nuclear Modifi-cation Factor?RAA?of D0 mesons in central Au+Au collisions at?^SNN?^1/2=200 GeV.In these dissertation,I also report the first measurement of A,production in heavy-ion collisions through the hadronic channel Ac+?p+K-?+.The invariant yield of Ac for 3<pT<6 GeV/c is measured in 10-60%central Au+Au collisions at?^SNN?^1/2=200 GeV.The ?c/D0 ratio is compared to different model calculations,and the physics implications are discussed.The first measurement of corrected spectra and RAA for D0 from HFT were shown,the precision was much better compared to previous published one.The new RAA re-sults show significant suppression at high pT which means the strong interaction be-tween charm quark and the medium and loose energy.While the D0 RAA shows quite similar trend as light hadrons.The efficiency corrected spectra for D± was also pre-sented.After taken into the charm fragmentation,the D± and D0 spectra have simi-lar/same shape,which means the production mechanism are similar for them.The first measurement of ?c in heavy-ion collisions was presented in this disser-tation.The enhancement of ?c/D0 ratio was compared to light hadrons and several dif-ferent models predictions.And the coalescence model with thermalized charm quarks are consistent with our data.From all the observed measurements from this dissertation together with our re-cently results on DOv2 charm quarks strongly coupled with the QGP and significantly loss energy.Evidence of charm quark flowing and possibly thermalized in the QGP.Which make charm quarks no big difference compare with light and strangeness quarks.Then a native question will be does charm quark heavy enough as a clean probe to de-terminate the QGP properties?Should we turn to even heavy quark such as bottom in the future?...