Nuclear Modification of Electron Spectra and Implications for Heavy Quark Energy Loss in Au+Au Collisions at sqrt(s_NN)=200 GeV

TL;DR

A significant suppression of electrons at high pT is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.

Abstract

The PHENIX experiment has measured mid-rapidity transverse momentum spectra (0.4 < p_T < 5.0 GeV/c) of electrons as a function of centrality in Au+Au collisions at sqrt(s_NN)=200 GeV. Contributions from photon conversions and from light hadron decays, mainly Dalitz decays of pi^0 and eta mesons, were removed. The resulting non-photonic electron spectra are primarily due to the semi-leptonic decays of hadrons carrying heavy quarks. Nuclear modification factors were determined by comparison to non-photonic electrons in p+p collisions. A significant suppression of electrons at high p_T is observed in central Au+Au collisions, indicating substantial energy loss of heavy quarks.

Figures (3)

• Figure 1: (Color online) Inclusive and non-photonic electron invariant yields in minimum bias Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, compared with contributions from all background electron sources included in the cocktail (a). Invariant yields of electrons from heavy flavor decays for different Au+Au centrality classes, scaled by powers of ten for clarity. Curves are the best fit to the p+p reference scaled with the appropriate nuclear overlap integrals $\langle T_{AA} \rangle$ (b). The error bars (brackets) correspond to statistical (systematic) uncertainties in both panels.
• Figure 2: Nuclear modification factor $R_{AA}$ for electrons from heavy flavor decays as function of $p_T$ in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV for the different centrality classes. The error bars are statistical only. Error brackets (boxes) indicate the systematic errors related to the uncertainties in the Au+Au (p+p) measurements. The bands around one show the relative systematic uncertainties in $T_{AA}$. For the most central collisions the $\pi^0$$R_{AA}$ is shown for comparison ppg014. For these data, a 13 % $p_T$ independent systematic uncertainty (not plotted) represents the uncertainty in $\langle T_{AA} \rangle$ and in the $\pi^0$ yield normalization.
• Figure 3: Nuclear modification factor $R_{AA}$ for electrons from heavy quark decays as function of $p_T$ for the 10 % most central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in comparison with predictions from models incorporating charm quark energy loss. The curves (1a-c) and (2a-b) are taken from armesto and magdalena, respectively, where contributions from $B$ meson decays are included in (2a-b) only. Experimental uncertainties are shown as described in Fig. \ref{['fig2']}.