Here are some diagonostic checks for the FMS simulation. The following is for small cells only.

Fig. 1 Distribution of x_recon - x_sim for photons. Seems that reconstructed x position is normally bigger than the simulated position. It needs further check.

Fig. 2 Distribution of y_recon - y_sim for photons. Looks better than x position.

Fig. 3 Distribution for reconstructed Dgg factor minus simulated Dgg factor.

Fig. 4. Distribution of reconstructed Zgg factor minus simulated Zgg factor.

Fig. 5. Distribution of reconstructed Pi0 energy minus simulated Pi0 energy.

The following figures are from ~15M MB Pythia events.

Fig. 6. Reconstructed two photon energy distribution.

Fig. 7. Reconstructed two photon mass distribution.

Fig. 8. Reconstructed two-photon mass distribution where both photons can be matched to a simulated photon.

Fig. 9. Reconstructed two-photon mass distribution where both photons are matched to a simulated photon and both the simulated photons are decay products of the same parent.