| Lattice QCD calculations predicted a phase transition from hadronic phase to a de-confined state of partonic matter phase,called the Quark-Gluon Plasma(QGP),at very high temperature and energy densities.Indication exists that such a state of matter is expected to be found at the very beginning of the Big Bang of the universe and could be found at the center of neutron stars,where the density of matter could be high enough for deconfinement.Heavy-Ion Collisions has been a unique experimental tool to create the QGP.The Relativistic Heavy Ion Collider,located at Brookhaven National Labora-tory,is a dedicated machine to study the QCD phase diagram and the properties of the deconfined matter in laboratory.Unlike light quarks,heavy quarks are expected to be created from initial hard scat-terings at the very early stages of the heavy-ion collisions and almost conserved through-out the expansion and their interactions with the medium.Their large masses are not easily affected by the strong interaction with QCD medium,hence are sensitive to the collision dynamics of the partonic matter at early stages.The interaction between heavy quarks and the medium is sensitive to the medium dynamics,therefore heavy quarks are suggested as an ideal probe to quantify the properties of the strongly interacting QCD matter.So far,there are two main questions concerning heavy-flavor interactions with the QGP medium.Firstly,the thermalization and hadronization of heavy quarks in the medium,which can be studied by measuring the baryon/meson ratio(?c/D for charm quark and Ab/B for beauty quark),the azimuthal anisotropy v2 for charm mesons and baryons,and the possible in-medium thermal production of charm quarks.Secondly,the heavy-quark in-medium energy loss and its mass dependence,which can be addressed by measuring the nuclear modification factors RAA for D and B mesons separately in a wide momentum range.In particular the Ds meson,the constituent quarks are cs/cs,production in heavy-ion collisions is expected to be sensitive to the enhanced strangeness production and to the hadronization mechanism of charm quarks.If the dominant mechanism for D-meson formation at low and intermediate momenta is in-medium hadronization of char-m quarks via recombination with light quarks.The relative yield of Ds+ mesons with respect to non-strange charmed mesons at low ?? is predicted to be enhanced in nucle-us-nucleus collisions as compared to pp interactions.Thus the modification of the Ds meson spectrum in heavy-ion collisions provides a new probe to study the charm-quark hadronization mechanism in the hot nuclear medium.Like multi-strange hadrons,the Ds meson will kinetically decouple close to the hadronization transition,while the non-strange D meson will pick up additional v2 from hadronic phases.Comparison of v2 between Ds meson and non-strange D meson can disentangle the contributions from the QGP and hadronic phases,and would allow a better quantification of the temperature dependence of viscosity-to-entropy ratio(?/s).In this thesis,we analyze the data collected with the STAR detector from(?)?200 GeV Au+Au collisions during the 14th RHIC run in 2014 using the new installed Heavy Flavor Tracker(HFT).The HFT detector is designed to extend STAR's capabili-ty of measuring heavy flavor production via the topological reconstruction of displaced decay vertices.It provides a unique opportunity for precise measurements of the Ds meson production in heavy-ion collisions at RHIC.This thesis report the first measure-ment Ds meson via the decay channel Ds??(1020)+ ??K-K+?-at mid-rapidity in Au+Au collisions at(?)=200 GeV,including the transverse momentum spec-tra,production ratio of Ds over non-strange D meson and elliptic flow(v2)as well as optimization of Ds reconstruction cuts by using TMVA package.Besides thesis mea-surements we also reported on the D+ transverse momentum spectra via the same decay channel as Ds+ and verified the efficiency calculation using data-driven method.The measured Ds+/D0 ratio is higher than that in p+p collisions predicted by PYTHIA at the intermediate ?? range,indicating an enhancement of Ds+ production in Au+Au col-lisions.The TAMU model seems to underestimate the observed enhancement below 4 GeV/c,while the enhancement seen in data at higher ?? remains a challenge for the model.Comparison to strange and light hadrons,the;Ds+/D0 is smaller than that of light and strange hadron yield ratios at low ?? range,while shows very similar amplitude in??>4 GeV/c.This indicates the charm quarks have very similar behavior as light and strange quarks,and provides a possible hint of that charm quark was equilibrated at QGP and consistent with the physics implemented from the measured D0 elliptic flow(v2).Besides,in this thesis,we developed two methods(direct and ?2 test)to estimate the bottom decay electron v2 for the first time at heavy-ion collisions.The estimation is based on STAR recent measured D0 transverse momentum spectra and v2 to estimate charm decay electron v2,then combining with the non-photonic electron(NPE)v2 and also the bottom decay electron over NPE ratio from PHENIX experiment to determine bottom decay electron v2.The obtained B meson decay electron v2 from direct method is systematically smaller than D decay electron v2 and consistent with zero within un-certainties.The ?2 method base on several assumption,and defined the parameter ? to qualify the amplitude of B decay electron v2.The ?2 test shows that the ? is trending towards to zero,that indicates the B decay electron v2 is zero.Both two methods sug-gest that the B meson decay electron v2 should be very small and consistent with zero,which probably because of that bottom is too heavy to be thermalized and is hard to participate in the collectivity in the medium.The D0 elliptic flow measured by STAR experiment suggests significant charm quark flow.Recent ALICE measurement also shows sizable charm flow at LHC energy.Both non-zero D0 v2 and zero B meson v2 will give a constraint to the degree of thermalization of the medium. |
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