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 MeV and 180 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 √ s N N = 200 GeV and Pb+Pb collisions at √ s N N = 2.76 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 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 .

Abstract. We calculate the heavy quark evolution in heavy ion collisions and show results for the elliptic flow v2 as well as the nuclear modification factor RAA at RHIC and LHC energies. For the calculation we implement a Langevin approach for the transport of heavy quarks in the UrQMD (hydrodynamics + Boltzmann) hybrid model. As drag and diffusion coefficients we use a Resonance approach for elastic heavy-quark scattering and assume a decoupling temperature of the charm quarks from the hot medium of 130 MeV. At RHIC energies we use a coalescence approach at the decoupling temperature for the hadronization of the heavy quarks to D-mesons and B-mesons and a sub-following decay to heavy flavor electrons using PYTHIA. At LHC we use an additional fragmentation mechanism to account for the higher transverse momenta reached at higher collision energies. IntroductionHeavy quarks are an ideal probe for the QGP. They are produced in the primordial hard collisions of the nuclear reaction and therefore probe the created medium during its entire evolution process. When the system cools down they hadronize, and their decay products can finally be detected. Therefore, heavy-quark observables provide new insights into the interaction processes within the hot and dense medium. Two of the most interesting observables are the elliptic flow, v 2 , and the nuclear modification factor, R AA , of open-heavy-flavor mesons and their decay products like "non-photonic" single electrons. The measured large elliptic flow, v 2 , of open-heavy-flavor mesons and the "non-photonic single electrons or muons" from their decay underline that heavy quarks take part in the collective motion of the bulk medium, consisting of light quarks and gluons. The nuclear modification factor shows a large suppression of the open-heavy flavor particles' spectra at high transverse momenta (p T ) compared to the findings in pp collisions. This also supports a high degree of thermalization of the heavy quarks with the bulk medium.In this letter we explore the medium modification of heavy-flavor p T spectra, using a hybrid model, consisting of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model [1,2] and a full (3+1)-dimensional ideal hydrodynamical model [3,4] to simulate the bulk medium. The heavy-quark propagation in the medium is described by a relativistic Langevin approach

We study J/Ψ absorption in high multiplicity proton-proton (pp) collisions at √ sNN = 7 TeV.We predict a modification of the J/Ψ-yield within the UrQMD transport approach, where explicit interactions of the J/Ψ with the surrounding comovers and a prehadronic phase with adjusted cross sections and J/Ψ melting is included. We present the analog of the nuclear modification factor in pp collisions at various charged particle multiplicities. It turns out that J/Ψ-Mesons may be suppressed towards higher particle multiplicities in pp collisions at LHC energies.

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