Energy Loss and Flow of Heavy Quarks in Au + Au Collisions at (S_(NN))~(1/2) = 200 Ge V

摘要

The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured electrons with 0.3 < p_T < 9 GeV/c at midrapidity (|y| < 0.35) from heavy-flavor (charm and bottom) decays in Au + Au collisions at (S_(NN))~(1/2) = 200 GeV. The nuclear modification factor R_(AA) relative to p + p collisions shows a strong suppression in central Au + Au collisions, indicating substantial energy loss of heavy quarks in the medium produced at RHIC energies. A large azimuthal anisotropy v_2 with respect to the reaction plane is observed for 0.5 < p_T < 5 GeV/c indicating substantial heavy-flavor elliptic flow. Both R_(AA) and v_2 show a p_T dependence different from those of neutral pions. A comparison to transport models which simultaneously describe R_(AA)(p_t) and v_2(p_T) suggests that the viscosity to entropy density ratio is close to the conjectured quantum lower bound, i.e., near a perfect fluid.