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Register a new userMeasurements of $e^+e^-$ pairs from open heavy flavor in $p$+$p$ and $d$+$A$ collisions at $sqrt{s_{NN}}=200$ GeV
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We report a measurement of $e^+e^-$ pairs from semileptonic heavy-flavor decays in $p$+$p$ collisions at $sqrt{s_{NN}}=200$~GeV. The $e^+e^-$ pair yield from $bbar{b}$ and $cbar{c}$ is separated by exploiting a double differential fit done simultaneously in dielectron invariant mass and $p_T$. We used three different event generators, {sc pythia}, {sc mc@nlo}, and {sc powheg}, to simulate the $e^+e^-$ spectra from $cbar{c}$ and $bbar{b}$ production. The data can be well described by all three generators within the detector acceptance. However, when using the generators to extrapolate to $4pi$, significant differences are observed for the total cross section. These difference are less pronounced for $bbar{b}$ than for $cbar{c}$. The same model dependence was observed in already published $d$+$A$ data. The $p$+$p$ data are also directly compared with $d$+$A$ data in mass and $p_T$, and within the statistical accuracy no nuclear modification is seen.
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We report $e^pm-mu^mp$ pair yield from charm decay measured between midrapidity electrons ($|eta|<0.35$ and $p_T>0.5$ GeV/$c$) and forward rapidity muons ($1.4<eta<2.1$ and $p_T>1.0$ GeV/$c$) as a function of $Deltaphi$ in both $p$$+$$p$ and in $d$+Au collisions at $sqrt{s_{_{NN}}}=200$ GeV. Comparing the $p$$+$$p$ results with several different models, we find the results are consistent with a total charm cross section $sigma_{cbar{c}} =$ 538 $pm$ 46 (stat) $pm$ 197 (data syst) $pm$ 174 (model syst) $mu$b. These generators also indicate that the back-to-back peak at $Deltaphi = pi$ is dominantly from the leading order contributions (gluon fusion), while higher order processes (flavor excitation and gluon splitting) contribute to the yield at all $Deltaphi$. We observe a suppression in the pair yield per collision in $d$+Au. We find the pair yield suppression factor for $2.7<Deltaphi<3.2$ rad is $J_{dA}$ = 0.433 $pm$ 0.087 (stat) $pm$ 0.135 (syst), indicating cold nuclear matter modification of $cbar{c}$ pairs.
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The sum of charm and beauty in Au+Au collisions at 200 GeV measured through nonphotonic electrons, show similar suppression at high pT as light hadrons, in contrast to expectations based on the dead cone effect. To understand this observation, it is important to separate the charm and beauty components. Non-photonic electron-D0 and electron-hadron azimuthal angular correlations are used to disentangle the contributions from charm and beauty decays. The beauty contribution in p+p collisions at 200 GeV is found to be comparable to charm at pT 5.5 GeV, indicating that beauty may contribute significantly to the non photonic electrons from heavy flavour decays in Au+Au data at high pT. Furthermore, in Au+Au collisions we present the status of D0 meson reconstruction using microvertexing techniques made possible with the addition of the silicon detectors.
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We report measurements of charmed-hadron ($D^{0}$, $D^{*}$) production cross sections at mid-rapidity in $p$ + $p$ collisions at a center-of-mass energy of 200 GeV by the STAR experiment. Charmed hadrons were reconstructed via the hadronic decays $D^{0}rightarrow K^{-}pi^{+}$, $D^{*+}rightarrow D^{0}pi^{+}rightarrow K^{-}pi^{+}pi^{+}$ and their charge conjugates, covering the $p_T$ range of 0.6$-$2.0 GeV/$c$ and 2.0$-$6.0 GeV/$c$ for $D^{0}$ and $D^{*+}$, respectively. From this analysis, the charm-pair production cross section at mid-rapidity is $dsigma/dy|_{y=0}^{cbar{c}}$ = 170 $pm$ 45 (stat.) $^{+38}_{-59}$ (sys.) $mu$b. The extracted charm-pair cross section is compared to perturbative QCD calculations. The transverse momentum differential cross section is found to be consistent with the upper bound of a Fixed-Order Next-to-Leading Logarithm calculation.
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