central arms of the PHENIX detector, each covering 90 degrees in azimuth and $|\eta|<0.35$ in pseudorapidity. The EMCal comprises two technologically different subsystems: lead-scintillator sampling calorimeter (PbSc) and lead-glass Čerenkov calorimeter (PbGl), which cover $3/8$ and $1/8$ of the full azimuth, respectively. The PbSc and PbGl subsystems have different linearity, energy resolution ($\delta E/E=2.1\%\oplus8.1\%/\sqrt{E}$ for PbSc and $0.8\%\oplus5.9\%/\sqrt{E}$ for PbGl) and segmentation ($\delta\phi\times\delta\eta \approx 0.01\times0.01 $ for PbSc and $ 
0.008\times0.008 $ for PbGl).

The raw yields of $\pi^0$ and $\eta$ mesons are determined from the $\gamma\gamma$ invariant mass ($m_{\rm inv}$) distribution, in bins of and centrality. The analysis is carried out independently for the PbSc and PbGl subsystems. Photon candidates have to satisfy a shower shape cut [@Aphecetche:2003zr] and are required to have energy ($E_{\gamma}$) larger than 0.4GeV, which helps to further reduce the contribution from other particles, mostly minimum ionizing hadrons. Each $\gamma\gamma$ pair is required to satisfy an asymmetry cut $|\alpha|<0.8$, where $\alpha=|E_{\gamma1}-E_{\gamma2}|/(E_{\gamma1}+E_{\gamma2})$. The asymmetry cut helps to reduce the background from combinatorial $\gamma\gamma$ pairs in the $m_{\rm inv}$ distributions, improving the $S/B$ ratio. A typical invariant mass distribution is shown in Fig. \[fig:FIG0\_InvMass\_Example\].

The $m_{\rm inv}$ distributions contain two peaks in the selected mass region, which 