$\bar N (\hat r-1)$ on $(\eta_{\Delta},\phi_{\Delta})$ for central (a) to peripheral (d) collisions. Center bins at $\phi_{\Delta} = \eta_{\Delta} = 0$, containing photon-conversion electron pairs, were omitted from model fits.](cdfitaya2 "fig:"){width="1.65in"} ![\[Figure2\] Perspective views of two-particle CD joint autocorrelations $\bar N (\hat r-1)$ on $(\eta_{\Delta},\phi_{\Delta})$ for central (a) to peripheral (d) collisions. Center bins at $\phi_{\Delta} = \eta_{\Delta} = 0$, containing photon-conversion electron pairs, were omitted from model fits.](cdfitaya3 "fig:"){width="1.65in"} ![\[Figure2\] Perspective views of two-particle CD joint autocorrelations $\bar N (\hat r-1)$ on $(\eta_{\Delta},\phi_{\Delta})$ for central (a) to peripheral (d) collisions. Center bins at $\phi_{\Delta} = \eta_{\Delta} = 0$, containing photon-conversion electron pairs, were omitted from model fits.](cdfitaya4 "fig:"){width="1.65in"}

Because of the symmetry of these distributions on the angular spaces $(x_1,x_2)$ their description is more natural on [*diagonal*]{} sum and difference variables $x_\Sigma$ and $x_\Delta$ (reserving conventional difference notation $\Delta x$ for displacement on a 1D space $x$). The invariance of correlation structure on sum variables $\eta_\Sigma \equiv \eta_1 + \eta_2$ and $\phi_\Sigma \equiv \phi_1 + \phi_2$ in Fig. \[Figure1\] ([*i.e.,*]{} parallel to the $\eta_1 = \eta_2$ or $\phi_1 = \phi_2$ diagonals) implies that each distribution can be projected onto its difference variable $\phi_{\Delta} \equiv \phi_1 - \phi_2$ and $\eta_{\Delta} 