Measurements Of Open Heavy Flavor Production In P+p And Au+Au Collisions At RHIC Energy

The primary motivation for relativistic heavy-ion collisions is to study the formation of theoretically predicted plasma of deconfined quarks and gluons(QGP)and the properties of the strongly interacting matter at extremely high temprature and energy density.Both the Relativistic Heavy Ion Collider(RHIC)at Brookhaven National Laboratory(BNL)and the Large Hadron Collider(LHC)experimental results suggest that such matter could be created in the relativistic heavy-ion collisions,however,such a medium can not be directly observed in the experiment,since the quarks and gluons with the color charges and can not exist from others,therefore,they can not be directly observed in the experiment,the only observation is the final state chemical freeze-out particles,however,the final states particles are affected by both the initial and final states nuclear matter effects.Heavy flavor quarks are suggested to be an excellent probe of the QGP,because they are produced very early in the heavy-ion collisions,therefore they carry the information about the early stages of the system evolution.They are expected to interact with the QGP differently from light quarks and their production is sensitive to the dynamics of the mediums.Measurements of the charm and bottom quark production are crucial for understanding the nature of interactions of heavy quarks with the surrounding partonic medium,and the partons energy loss mechanism.Precise measurements of cham and bottom quark production separately in heavy-ion collisions is crucial for understanding the flavor dependent parton energy loss mechanism,and improve our understanding of the properties of the QGP.Because heavy quarks masses(cham and bottom quarks,mc≈1.3 GeV/c2 and mb≈4.2 GeV/c2)are much higher than the typical QCD scale 200 MeV,heavy flavor quarks production is expected to be well described by the perturbative QCD.High precision measurements of heavy flavor production in proton-proton collisions are instrumental to test the validity and constrain the parameters of perturbative QCD calculations.The Heavy Flavor rTracker(HFT),installed at the STAR experiment since 2014,pro-vides excellent resolution to measure the Distance of Closest Approach(DCA)between primavry vertices and secondary decay vertex.It enables the separation of non-photonic electron(NPE)produced from D-and B-meson decays.Electrons from semi-leptonic decays of heavy flavor hadrons(non-photonic electrons,NPE)are good proxies for heavy quarks.Although the kinematics information of parent heavy flavor hardrons is incom-plete,NPE is still the most feasible tool so far to study heavy quark production at RHIC energies,especially at high pT。and dedicated triggers for such electrons can be used in the experiment to largely enhance the statistics.Unless specified otherwise,electrons referred here include both electrons and positrons.The latest data analysis results extend the pT coverage to lower and higher values than previous STAR measurements with significantly better precision is consistent with the FONLL calculations,moreover,it provides a baseline for the interpretation of heavy flavor production in nucleus-nucleus collisions.The measured nuclear modification factors RAA indicate an significant suppression at pT>4 GeV/c in the most central Au+Au collisions,and reduces gradually towards more peripheral collisions,enhancement at low prT across all centrality bins but with large systematic uncertainties.Nuclear modification factors RAA for D-and B-decayed electrons are obtained,suggesting less suppression for B-decayed electrons than D-decayed electrons and consistent with the mass hirechy of parton energy loss △Eb<△Ec.