$\sigma_{\phi_\Delta}$ and $\sigma_{\eta_\Delta}$ are the r.m.s. widths of the 2D exponential peak when projected onto the respective difference variables.

Best-fit values for varied parameters and $\chi^2/$DoF for the four centralities are listed in Table \[TableI\]. The width of the 1D gaussian, most evident near $|\phi_\Delta| \sim \pi$ in Fig. 2(d), was best determined by those peripheral data to be $1.5\pm0.25$ and was held fixed at that value for the other centralities to obtain the amplitude estimates. The observed peripheral Au-Au $\phi_\Delta$ width is definitely larger than the corresponding width for p-p collisions. Also included is tracking efficiency-correction factor ${\tilde S}$ [@extrap]. Total systematic error for efficiency-corrected amplitudes in Table \[TableI\] was 11% (errors added in quadrature). The model fits indicate that with increasing centrality the 2D exponential peak exhibits 1) strong amplitude increase, 2) significant width reduction and 3) approach to approximately equal widths on $\phi_{\Delta}$ and $\eta_{\Delta}$ for central collisions ([*cf.*]{} Fig. \[Figure3\]; [*e.g.,*]{} at mid-rapidity $\sigma_{\eta_\Delta} = 0.6$ corresponds to polar angle difference $0.57$, which is directly comparable to $\sigma_{\phi_\Delta}$).

          centrality                 (d)                 (c)                 (b)                 (a)           error[^1](%)
  -------------------------- ------------------- ------------------- ------------------- ------------------- ----------------
    ${\tilde S}$ [@extrap]          1.19                1.22                1.25                1.27            8 (syst.)
          $\bar{N}$                 115.5               424.9               789.3               983.0        
                                                                                                             
   ${\tilde S} 