projection technique is a [*nearly lossless*]{} (distortion free) projection from the initial 4D angular subspace onto a 2D autocorrelation space.

In this analysis, sibling and mixed pair-number densities $\rho(\vec{p}_1,\vec{p}_2)$ for four charge-pair combinations $(++,+-,-+,--)$ were projected onto $(\eta_1,\eta_2)$, $(\phi_1,\phi_2)$ and $(\eta_\Delta,\phi_\Delta)$. The projection was done by filling histograms of pair numbers $n_{ab} \simeq  \epsilon_x \, \epsilon_y \,\rho(x_a,y_b)$, where subscripts $ab$ denote the 2D bin indices and $\epsilon_x, \epsilon_y$ are histogram bin widths on variables $x,y \in \{\eta_1, \eta_2, \phi_1, \phi_2, \eta_\Delta, \phi_\Delta\}$. Sibling and mixed pair-number histograms for each charge-pair combination were separately normalized to the total number of detected pairs in each centrality class: $\hat n_{ab,sib} = n_{ab,sib} / \sum_{ab} n_{ab,sib}$ and $\hat n_{ab,mix} = n_{ab,mix} / \sum_{ab} n_{ab,mix}$. Normalized pair-number ratios $\hat{r}_{ab} = \hat{n}_{ab,sib}/\hat{n}_{ab,mix}$ are the basis for this analysis.

To reduce systematic error, ratio histograms were obtained for subsets of events within a given centrality class which have similar multiplicities (differences $\leq 50$) and primary collision vertex locations within the detector (within 7.5 cm along the beam axis). Ratios $\hat r_{ab}$ for each centrality class were defined as weighted (by total number of sibling pairs) averages over all subsets in that centrality class. Ratios were further combined 