Measurement of $D^0$-meson $+$ hadron two-dimensional angular correlations in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200$ GeV

Open heavy-flavor hadrons provide unique probes of the medium produced in ultrarelativistic heavy-ion collisions. Due to their increased mass relative to light-flavor hadrons, long lifetime, and early production in hard-scattering interactions, they provide access to the full evolution of the partonic medium formed in heavy-ion collisions. This paper reports two-dimensional (2D) angular correlations between neutral $D$ mesons and unidentified charged particles produced in minimum-bias $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$. $D^0$ and ${\overline{D}}^0$ mesons are reconstructed via their weak decay to $K^{\mp }{\pi }^{\pm }$ using the Heavy Flavor Tracker in the Solenoidal Tracker at RHIC experiment. Correlations on relative pseudorapidity and azimuth $(\mathrm{\Delta }\eta ,\mathrm{\Delta }\varphi )$ are presented for peripheral, midcentral, and central collisions with $D^0$ transverse momentum from $2–10\mathrm{GeV}/c$. Attention is focused on the 2D peaked correlation structure near the triggered $D^0$ meson, the near-side (NS) peak, which serves as a proxy for a charm-quark-containing jet. The correlated NS yield of charged particles per $D^0$ meson and the 2D widths of the NS peak increase significantly from peripheral to central collisions. These results are compared with similar correlations using unidentified charged particles, consisting primarily of light-flavor hadrons, at similar trigger particle momenta. Similar per-trigger yields and widths of the NS correlation peak are observed. The present results provide additional evidence that $D^0$ mesons undergo significant interactions with the medium formed in heavy-ion collision and show, for the first time, significant centrality evolution of the NS 2D peak in the correlations of particles associated with a heavy-flavor hadron produced in these collisions.

Figure 1

$D^0$ decay diagram depicting the five topological reconstruction cuts [6]: (i) decay length, (ii) DCA between decay daughters (${\mathrm{DCA}}_{12}$), (iii) DCA of reconstructed $D^0$ to PV, where $\theta$ (the angle between the $D^0$ momentum vector and the straight line between the primary and $D^0$ decay vertices) and the decay length are used in the calculation, (iv) DCA of daughter pion to PV, and (v) DCA of daughter kaon to PV.

Figure 2

Invariant mass distributions for the three centrality classes used in this analysis from peripheral to central in the upper to lower rows of panels, respectively. The US (dots) and normalized LS (triangles) distributions are shown in the left-hand column, and the LS $+$ linear background subtracted distributions are shown in the right-hand column. The linear background fit functions for the residual background after subtraction of the normalized LS distributions are shown by the straight lines in the left-hand panels.

Figure 3

$D^0+h^{\pm }$ correlation data (left column), model fits (middle column), and residuals in units of $\left|n\sigma \right|$ per bin (right column). Centrality fractions are 50–80 %, 20–50 %, and 0–20 % from top to bottom rows, respectively.

Figure 4

Extracted fit values for the quadrupole amplitude ($A_Q$) and the 2D widths of the NS jetlike peak (${\sigma }_{\mathrm{\Delta }\varphi ,NS}, {\sigma }_{\mathrm{\Delta }\eta ,NS}$) from the present analysis (stars). Left: Quadrupole amplitude, Middle: NS peak width on $\mathrm{\Delta }\varphi$, Right: NS peak width on $\mathrm{\Delta }\eta$. Each plot also shows pythia predictions [44, 45] (upright triangles), dihadron results [46] for $\langle p_T\rangle =2.56\mathrm{GeV}/c$ (upside down triangles), and dihadron results for $\langle p_T\rangle =5.7\mathrm{GeV}/c$ (dots). Horizontal bars indicate the differing centrality ranges for the present analysis and those in Ref. [46]; vertical bars show the statistical errors, and cross bars show the systematic uncertainties.

Figure 5

Correlated hadron yield per $D^0$ trigger in the near-side 2D Gaussian peak for the present data (stars), pythia [44, 45] predictions (upright triangle), dihadron results [46] for $\langle p_T\rangle =2.56\mathrm{GeV}/c$ (upside down triangles), and dihadron results for $\langle p_T\rangle =5.7\mathrm{GeV}/c$ (dots). Horizontal bars indicate the centrality ranges; vertical bars show the statistical errors, and cross bars show the systematic uncertainties.

Figure 6

pythia [44, 45] predictions for $D^0 +$ hadron 2D angular correlations in minimum-bias $\mathrm{p}+\mathrm{p}$ collisions at $\sqrt{s}=200$ GeV in which a $D^0\to K+\pi$ decay is produced (left panel), as well as the model fit, residuals, and $n\sigma$'s of the residuals from left to right, respectively.