Abstract
The PHENIX experiment at the BNL Relativistic Heavy Ion Collider (RHIC) has measured electrons with at midrapidity () from heavy-flavor (charm and bottom) decays in collisions at . The nuclear modification factor relative to collisions shows a strong suppression in central collisions, indicating substantial energy loss of heavy quarks in the medium produced at RHIC energies. A large azimuthal anisotropy with respect to the reaction plane is observed for indicating substantial heavy-flavor elliptic flow. Both and show a dependence different from those of neutral pions. A comparison to transport models which simultaneously describe and suggests that the viscosity to entropy density ratio is close to the conjectured quantum lower bound, i.e., near a perfect fluid.
- Received 11 November 2006
DOI:https://doi.org/10.1103/PhysRevLett.98.172301
©2007 American Physical Society