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

TL;DR

This study measures electrons from heavy-flavor decays at midrapidity in $p+p$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV to probe heavy-quark interactions with the quark–gluon plasma. The analysis combines converter and cocktail background subtraction, leverages detector simulations for acceptance and efficiency corrections, and extracts $R_{AA}$ and $v_2$ for heavy flavor over a broad $p_T$ range. The results show strong suppression at high $p_T$ and a sizeable, rising $v_2$ at low $p_T$, indicating substantial heavy-quark energy loss and significant coupling to the medium, which are interpreted within Langevin, coalescence, and resonance-based transport frameworks. The findings constrain the heavy-quark diffusion coefficient and imply a low viscosity-to-entropy ratio near the conjectured bound, reinforcing the picture of a strongly interacting, near-perfect fluid created in RHIC collisions. Future measurements separating charm and bottom will sharpen the understanding of heavy-quark dynamics in the QGP.

Abstract

Transverse momentum (p^e_T) spectra of electrons from semileptonic weak decays of heavy flavor mesons in the range of 0.3 < p^e_T < 9.0 GeV/c have been measured at mid-rapidity (|eta| < 0.35) by the PHENIX experiment at the Relativistic Heavy Ion Collider in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The nuclear modification factor R_AA with respect to p+p collisions indicates substantial energy loss of heavy quarks in the produced medium. In addition, the azimuthal anisotropy parameter v_2 has been measured for 0.3 < p^e_T < 5.0 GeV/c in Au+Au collisions. Comparisons of R_AA and v_2 are made to various model calculations.

Figures (46)

• Figure 1: (Color online) Beam view (at $z=0$) of the PHENIX central arm detector in 2004 (Au+Au) and 2005 ($p$+$p$). The detectors used in the present analysis are the drift chamber (DC) and the multiwire proportional pad chambers (PC1, PC2, PC3) for charged particle tracking, the ring-imaging Čerenkov detector (RICH) for electron identification, and the electromagnetic calorimeters, which are Lead Glass (PbGl) and Lead Scintillator (PbSc), for energy measurement.
• Figure 2: (Color online) Top view (at $y=0$) of the ring-imaging Čerenkov detector (RICH) in the PHENIX East arm.
• Figure 3: (Color online) The correlation between fractional BBC charge Q/Q$_{\rm max}$ and fractional of ZDC energy E/E$_{\rm max}$. The sections from right to left correspond to centrality classes 0--10 %, 10--20 %, 20--40 %, 40--60 %, and 60--92 %.
• Figure 4: (Color online) A charged particle trajectory and the kinematic parameters are shown in (a) beam view, (b) side view, and (c) top view of PHENIX central region.
• Figure 5: (Color online) E/p distributions for various $p_T\xspace$ ranges. (a) and (b) are for Au+Au collisions. (c) is for $p+p$ collisions, where the black stars are the data points and the solid circles show the GEANT GEANT01:W5013 simulation. The triangles and squares show the contributions from simulation of $\pi^0$ and $K_{e3}$, respectively. See text for more details.