Product of acceptance and efficiency for $\Dzero$ mesons in Pb-Pb collisions for 30-50% centrality class (upper panel). The rapidity interval is $|y|< y_{\rm fid}$ (see text for details). The values for prompt (solid lines) and feed-down (dotted lines) $\Dzero$ mesons are shown. Also displayed, for comparison, are the values for prompt $\Dzero$ mesons without PID selection (dashed lines). The lower panel shows the ratio of the efficiencies for prompt $\Dzero$ mesons in the in-plane and out-of-plane regions used for the analysis. This ratio was estimated using simulation samples with a difference in particle multiplicity similar to that observed in data for the two azimuthal regions.