Centrality Dependence of Charm Production from a Measurement of Single Electrons in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$

The PHENIX experiment has measured midrapidity transverse momentum spectra ($0.4<p_T<4.0\mathrm{G}\mathrm{e}\mathrm{V}/c$) of single electrons as a function of centrality in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. Contributions from photon conversions and Dalitz decays of light neutral mesons are measured by introducing a thin (1.7% $X_0$) converter into the PHENIX acceptance and are statistically removed. The subtracted nonphotonic electron spectra are primarily due to the semileptonic decays of hadrons containing heavy quarks, mainly charm at lower $p_T$. For all centralities, the charm production cross section is found to scale with the nuclear overlap function, $T_{AA}$. For minimum-bias collisions the charm cross section per binary collision is $N_{c\overline{c}}/T_{AA}=622\pm 57(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 160(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})\mu \mathrm{b}$.

Figure 1

Shown vs $p_T$ (a) raw $e^{\pm }$ spectra measured with the converter in (open circles) and out (closed circles). (b) Ratio of the converter in/out $e^{\pm }$ yields ($R_{CN}$, points) and ratio of photonic $e^{\pm }$ yield with/without the converter ($R_{\gamma }$, line and shaded band). (c) Ratio of nonphotonic to photonic $e^{\pm }$ yields ($R_{NP}$, points) and contribution from kaon decays (dashed line).

Figure 2

Fully corrected charm electron $p_T$ spectra for different $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ centralities scaled by successive factors of 10 for clarity. Error bars (brackets) correspond to statistical (systematic) uncertainties. Curves are described in the text.

Figure 3

Charm electron yield ($0.8<p_T<4.0\mathrm{G}\mathrm{e}\mathrm{V}/c$) measured in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at 200 GeV scaled by $N_{\mathrm{c}\mathrm{o}\mathrm{l}\mathrm{l}}$ as a function of $N_{\mathrm{c}\mathrm{o}\mathrm{l}\mathrm{l}}$ (left-hand scale). Normalizing instead by the nuclear overlap function we obtain charm electron cross section per $N+N$ collision (right-hand scale).