Projections of $R_2^{\rm (CD)}$ correlation functions, measured in \PbPb\ collision at $\sqrt{s_{NN}} = 2.76$ TeV, for selected ranges of collisioncentrality. The $\Delta\eta$ and $\Delta\varphi$ projections are calculated as averages of the two-dimensional correlations in the ranges $|\Delta \varphi| \le \pi$ and $|\Delta \eta| \le 1.8$, respectively. Vertical bars and shaded areas represent statistical and systematic uncertainties, respectively. | |