Observation of $D^0$ Meson Nuclear Modifications in $\mathrm{Au}+\mathrm{Au}$ Collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$

We report the first measurement of charmed-hadron ($D^0$) production via the hadronic decay channel ($D^0\to K^{-}+{\pi }^{+}$) in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ with the STAR experiment. The charm production cross section per nucleon-nucleon collision at midrapidity scales with the number of binary collisions, $N_{\mathrm{bin}}$, from $p+p$ to central $\mathrm{Au}+\mathrm{Au}$ collisions. The $D^0$ meson yields in central $\mathrm{Au}+\mathrm{Au}$ collisions are strongly suppressed compared to those in $p+p$ scaled by $N_{\mathrm{bin}}$, for transverse momenta $p_T>3\mathrm{GeV}/c$, demonstrating significant energy loss of charm quarks in the hot and dense medium. An enhancement at intermediate $p_{\mathrm{T}}$ is also observed. Model calculations including strong charm-medium interactions and coalescence hadronization describe our measurements.

Figure 1

Panel (a): Invariant mass distribution for all the combinations of kaon and pion candidates (solid circles). The ME technique reproduces the combinatorial background as shown by the curve. The distribution after ME background subtraction is shown as open circles. Panel (b): $M_{K\pi }$ distribution after ME background subtraction (solid circles) and after further residual background subtraction (open circles). Panels (c), (d), and (e) are $M_{K\pi }$ distributions for the 0%–10% most-central collisions in three $p_{\mathrm{T}}$ regions.

Figure 2

Centrality dependence of the $D^0$ $p_{\mathrm{T}}$ differential invariant yield in $\mathrm{Au}+\mathrm{Au}$ collisions (solid symbols). The curves are number-of-binary-collision-scaled Levy functions from fitting to the $p+p$ result (open circles) [23]. The arrow denotes the upper limit with a 90% confidence level of the last data point for 10%–40% collisions. The systematic uncertainties are shown as square brackets.

Figure 3

Panels (a,b): $D^0$ $R_{\mathrm{AA}}$ for peripheral 40%–80% and semicentral 10%–40% collisions. Panel (c): $D^0$ $R_{\mathrm{AA}}$ for 0%–10% most-central events (blue circles) compared with model calculations from the TAMU (solid curve), SUBATECH (dashed curve), Torino (dot-dashed curve), Duke (long-dashed and long-dot-dashed curves), and LANL groups (filled band). The vertical lines and boxes around the data points denote the statistical and systematic uncertainties. The vertical bars around unity denote the overall normalization uncertainties in the $\mathrm{Au}+\mathrm{Au}$ and $p+p$ data, respectively.

Figure 4

Integrated $D^0$ $R_{\mathrm{AA}}$ as a function of $N_{\text{part}}$ in different $p_{\mathrm{T}}$ regions: $0–8\mathrm{GeV}/c$ (squares), $3–8\mathrm{GeV}/c$ (circles), and $0.7–2.2\mathrm{GeV}/c$ (diamonds). Open symbols are for the 0%–80% MB events.