Single electrons from heavy-flavor mesons in relativistic heavy-ion collisions

Abstract

We study the single electron spectra from $D\ensuremath{-}$ and $B\ensuremath{-}$meson semileptonic decays in $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=200$, 62.4, and 19.2 GeV by employing the parton-hadron-string dynamics (PHSD) transport approach that has been shown to reasonably describe the charm dynamics at Relativistic Heavy Ion Collider and Large Hadron Collider energies on a microscopic level. In this approach the initial charm and bottom quarks are produced by using the PYTHIA event generator which is tuned to reproduce the fixed-order next-to-leading logarithm calculations for charm and bottom production. The produced charm and bottom quarks interact with off-shell (massive) partons in the quark-gluon plasma with scattering cross sections which are calculated in the dynamical quasiparticle model that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature ${T}_{c}$. At energy densities close to the critical energy density ($\ensuremath{\approx}0.5\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}/{\mathrm{fm}}^{3}$) the charm and bottom quarks are hadronized into $D$ and $B$ mesons through either coalescence or fragmentation. After hadronization the $D$ and $B$ mesons interact with the light hadrons by employing the scattering cross sections from an effective Lagrangian. The final $D$ and $B$ mesons then produce single electrons through semileptonic decay. We find that the PHSD approach well describes the nuclear modification factor ${R}_{\mathrm{AA}}$ and elliptic flow ${v}_{2}$ of single electrons in $d+\text{Au}$ and $\text{Au}+\text{Au}$ collisions at $\sqrt{{s}_{\mathrm{NN}}}=200\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}$ and the elliptic flow in $\text{Au}+\text{Au}$ reactions at $\sqrt{{s}_{\mathrm{NN}}}=62.4\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}$ from the PHENIX Collaboration, however, the large ${R}_{\mathrm{AA}}$ at $\sqrt{{s}_{\mathrm{NN}}}=62.4\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}$ is not described at all. Furthermore, we make predictions for the ${R}_{\mathrm{AA}}$ of $D$ mesons and of single electrons at the lower energy of $\sqrt{{s}_{\mathrm{NN}}}=19.2\phantom{\rule{0.28em}{0ex}}\mathrm{GeV}$. Additionally, the medium modification of the azimuthal angle $\ensuremath{\phi}$ between a heavy quark and a heavy antiquark is studied. We find that the transverse flow enhances the azimuthal angular distributions close to $\ensuremath{\phi}=0$ because the heavy flavors strongly interact with nuclear medium in relativistic heavy-ion collisions and almost flow with the bulk matter.