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Register a new userCentrality and transverse momentum dependence of $D^0$-meson production at mid-rapidity in Au+Au collisions at ${sqrt{s_{rm NN}} = rm{200,GeV}}$
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We report a new measurement of $D^0$-meson production at mid-rapidity ($|y|$,$<$,1) in Au+Au collisions at ${sqrt{s_{rm NN}} = rm{200,GeV}}$ utilizing the Heavy Flavor Tracker, a high resolution silicon detector at the STAR experiment. Invariant yields of $D^0$-mesons with transverse momentum $p_{T}$ $lesssim 9$,GeV/$c$ are reported in various centrality bins (0--10%, 10--20%, 20--40%, 40--60% and 60--80%). Blast-Wave thermal models are used to fit the $D^0$-meson $p_{T}$ spectra to study $D^0$ hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons ($pi,K$ and $p$), but comparable to that of hadrons containing multiple strange quarks ($phi,Xi^-$), indicating that $D^0$ mesons kinetically decouple from the system earlier than light hadrons. The calculated $D^0$ nuclear modification factors re-affirm that charm quarks suffer large amount of energy loss in the medium, similar to those of light quarks for $p_{T}$,$>$,4,GeV/$c$ in central 0--10% Au+Au collisions. At low $p_{T}$, the nuclear modification factors show a characteristic structure qualitatively consistent with the expectation from model predictions that charm quarks gain sizable collective motion during the medium evolution. The improved measurements are expected to offer new constraints to model calculations and help gain further insights into the hot and dense medium created in these collisions.
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We report on the first measurement of the charmed baryon $Lambda_c^{pm}$ production at midrapidity ($|y|$ $<$ 1) in Au+Au collisions at $sqrt{s_{NN}}$ = 200 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider. The $Lambda_c$/$D^0$ (denoting ($Lambda_c^++Lambda_c^-$)/($D^0+bar{D^0}$)) yield ratio is measured to be 1.08 $pm$ 0.16 (stat.) $pm$ 0.26 (sys.) in the 0--20% most central Au+Au collisions for the transverse momentum ($p_T$) range 3 $<$ $p_T$ $<$ 6 GeV/$c$. This is significantly larger than the PYTHIA model calculations for $p+p$ collisions. The measured $Lambda_c$/$D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au+Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured $Lambda_c$/$D^0$ ratio.
Due to the large masses, heavy-flavor quarks are dominantly produced in initial hard scattering processes and experience the whole evolution of the medium produced in heavy-ion collisions at RHIC energies. They are also expected to thermalize slower than light-flavor quarks. Thus the measurement of heavy quark production and azimuthal anisotropy can provide important insights into the medium properties through their interactions with the medium. In these proceedings, we report measurements of $D^0$ production and elliptic flow ($v_2$) via topological reconstruction using STARs recently installed Heavy Flavor Tracker (HFT). The new measurement of the nuclear modification factor ($R_{AA}$) of $D^0$ mesons in central Au+Au collisions at $sqrt{s_{NN}}$ = 200 GeV confirms the strong suppression at high transverse momenta ($p_{T}$) reported in the previous publication with much improved precision. We also report the measurement of elliptic flow for $D^0$ mesons in a wide transverse momentum range in 0-80% minimum-bias Au+Au collisions. The $D^0$ elliptic flow is finite for $p_{T}$ $>$ 2 GeV/c and is systematically below that of light hadrons in the same centrality interval. Furthermore, several theoretical calculations are compared to both $R_{AA}$ and $v_2$ measurements, and the charm quark diffusion coefficient is inferred to be between 2 and $sim$12.
We have measured the distributions of protons and deuterons produced in high energy heavy ion Au+Au collisions at RHIC over a very wide range of transverse and longitudinal momentum. Near mid-rapidity we have also measured the distribution of anti-protons and anti-deuterons. We present our results in the context of coalescence models. In particular we extract the volume of homogeneity and the average phase-space density for protons and anti-protons. Near central rapidity the coalescence parameter $B_2(p_T)$ and the space averaged phase-space density $<f> (p_T)$ are very similar for both protons and anti-protons. For protons we see little variation of either $B_2(p_T)$ or the space averaged phase-space density as the rapidity increases from 0 to 3. However both these quantities depend strongly on $p_T$ at all rapidities. These results are in contrast to lower energy data where the proton and anti-proton phase-space densities are different at $y$=0 and both $B_2$ and $f$ depend strongly on rapidity.
We report on the measurements of production of various charmed hadrons in Au+Au collisions at $sqrt{s_{rm{NN}}}$ = 200 GeV (including $D^{0}(overline{D^{0}})$ and $Lambda_{c}^{pm}$) obtained via topological reconstruction, utilizing the Heavy Flavor Tracker at STAR. Precise results on the $D^{0}$ yields from the 2014 data are reported for a wide transverse momentum range down to 0 in various centrality bins. With the high-statistics data collected in 2014 and 2016, and the usage of a supervised machine learning algorithm for signal-to-background separation, the first measurement of the centrality and transverse momentum dependences of $Lambda_{c}^{pm}$ production is shown. Finally, the total charm quark cross section extracted from these measurements in Au+Au collisions at $sqrt{s_{rm{NN}}}$ = 200 GeV is presented.
Heavy-flavor quarks are dominantly produced in initial hard scattering processes and experience the whole evolution of the system in heavy-ion collisions at RHIC energies. Thus they are suggested to be an excellent probe to the medium properties through their interaction with the medium. In this proceedings, we report our first measurement of $D^0$ production via topological reconstruction using STARs recently installed Heavy Flavor Tracker (HFT). We also report our new measurement of Nuclear Modification Factor ($R_{AA}$) of $D^0$ mesons in central Au+Au collisions at $sqrt{s_{NN}}$ = 200 GeV as a function of transverse momentum ($p_{T}$). New results confirm the strong suppression at high $p_{T}$ with a much improved precision, and show that the $R_{AA}$ at high $p_{T}$ are comparable with light hadrons ($pi$) and with D meson measurements at the LHC. Furthermore, several theoretical calculations are compared to our data, and with charm diffusion coefficient 2${pi}TD_{S}$ $sim$ 2-12 can reproduce both the $D^0$ $R_{AA}$ and $v_2$ data in Au+Au collisions at RHIC.
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