Heavy-Quark Diffusion and flow in the Quark-Gluon Plasma
Hendrik van Hees
Texas A&M University
In the investigation of the properties of the hot and dense state of matter (quark-gluon plasma), created in ultrarelativistic heavy-ion collisions, charm and bottom quarks are valuable probes since they are produced during the early stages of the reaction. The theory of heavy-quark interactions within the QGP is challenged by recent experimental results about the transverse-momentum spectra (R_AA) and elliptic flow (v_2) of non-photonic electrons, whose main sources are the decay of open-charm and -bottom mesons, from the STAR and PHENIX collaborations at the BNL Relativistic Heavy Ion Collider (RHIC), indicating a strong interaction of the heavy quarks with the quark-gluon plasma, driving them quickly towards thermal equilibrium. In this talk I will discuss a model, based on the assumption that D- and B-meson like resonance states survive the hadron-QGP phase transition, fascilitating heavy-quark thermalization through elastic rescattering with light quarks and anti-quarks in the medium. The heavy-quark-resonance interactions are described within a model based on chiral and spin symmetry as well as heavy-quark effective theory. The corresponding cross sections are used to evaluate friction and diffusion coefficients for a relativistic Fokker-Planck equation which is solved by an equivalent Langevin simulation to describe heavy-quark diffusion within a quark-gluon plasma including asymmetric (elliptic) flow. The c and b quarks are hadronized through a combined quark-coalescence-fragmentation model, and the single-electron spectra resulting from the pertinent non-photonic decays of D- and B-meson states are confronted with the experimental findings at RHIC.