Heavy quark transport in heavy ion collisions at RHIC and LHC within the   UrQMD transport model
  We have implemented a Langevin approach for the transport of heavy quarks in the UrQMD hybrid model. The UrQMD hybrid approach provides a realistic description of the background medium for the evolution of relativistic heavy ion collisions. We have used two different sets of drag and diffusion coefficients, one based on a $T$-Matrix approach and one based on a resonance model for the elastic scattering of heavy quarks within the medium. In case of the resonance model we have investigated the effects of different decoupling temperatures of the heavy quarks from the medium, ranging between $130\,\text{MeV}$ and $180\,\text{MeV}$. We present calculations of the nuclear modification factor $R_{AA}$, as well as of the elliptic flow $v_2$ in Au+Au collisions at $\sqrt{s_{NN}}=200\,\text{GeV}$ and Pb+Pb collisions at $\sqrt{s_{NN}}=2.76\,\text{TeV}$. To make our results comparable to experimental data at RHIC and LHC we have implemented a Peterson fragmentation and a quark coalescence approach followed by the semileptonic decay of the D- and B-mesons to electrons. We find that our results strongly depend on the decoupling temperature and the hadronization mechanism. At a decoupling temperature of $130\,\text{MeV}$ we reach a good agreement with the measurements at both, RHIC and LHC energies, simultaneously for the elliptic flow $v_2$ and the nuclear modification factor $R_{AA}$. 
Thomas Lang, Hendrik van Hees, Jan Steinheimer, Marcus Bleicher
hep-ph nucl-th