Energy Loss and Flow of Heavy Quarks in Au+Au Collisions at sqrt(s_NN) = 200 GeV

Abstract

The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured electrons from heavy flavor (charm and bottom) decays for 0.3 < p_T < 9 GeV/c at midrapidity (|y| < 0.35) in Au+Au collisions at sqrt(s_NN) = 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. A large azimuthal anisotropy, v_2, with respect to the reaction plane is observed for 0.5 < p_T < 5 GeV/c indicating non-zero 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.

Figures (3)

• Figure 1: Invariant yields of electrons from heavy-flavor decays for different Au+Au centrality classes and for $p$+$p$ collisions, scaled by powers of ten for clarity. The solid lines are the result of a FONLL calculation normalized to the $p$+$p$ data ppg065 and scaled with $\langle T_{\rm AA} \rangle$ for each Au+Au centrality class. The insert shows the ratio of heavy-flavor to background electrons for minimum bias Au+Au collisions. Error bars (boxes) depict statistical (systematic) uncertainties.
• Figure 2: $R_{\rm AA}$ of heavy-flavor electrons with $p_{\rm T}$ above 0.3 and 3 GeV/$c$ and of $\pi^0$ with $p_{\rm T} > 4$ GeV/$c$ as function of centrality given by $N_{\rm part}$. Error bars (boxes) depict statistical (point-by-point systematic) uncertainties. The right (left) box at $R_{\rm AA} = 1$ shows the relative uncertainty from the $p$+$p$ reference common to all points for $p_{\rm T} > 0.3 (3)$ GeV/$c$.
• Figure 3: (a) $R_{\rm AA}$ of heavy-flavor electrons in 0-10% central collisions compared with $\pi^0$ data ppg014 and model calculations (curves I Armesto:2005mz, II vanHees, and III Moore:2004tg). The box at $R_{\rm AA} = 1$ shows the uncertainty in $T_{AA}$. (b) $v_2^{\rm HF}$ of heavy-flavor electrons in minimum bias collisions compared with $\pi^0$ data ppg046 and the same models. Errors are shown as in Fig. \ref{['fig2']}.