Keith and I have looked at a few ways to clean up the invarient mass plots for EEmc pi0s.  It'd be good to check the effect of these cuts on the purity and efficiency using MC data.  For this blog, I'll just list the cuts that are used and show the invarient mass distributions.

Cuts

Instead of the cuts used by Weihong, the following plots have been made using the cuts:

• photon energies > 3 GeV,
• pi0 p_T > 4 GeV
• M_gg < 0.6 GeV
• 4 cm < D_gg < 25 cm (D_gg is distance between the two gammas)
• M_gg > 0.005 [GeV] + 0.004 [GeV/cm] D_gg
• Preshower energy for the towers under the two photons each < 40 MeV
• Energy in SMD for each photon / photon energy > 0.012 for each photon

Note, there is no longer a cut on the photons being in the same sector.  [EDIT (06/26/2012): the M_gg vs D_gg cut is based on a bug.  Cuts now need to be re-evaluated.]

Results

The first page of the attached PDFs have the mass distribution for all pT bins, while the later pages show the results for each pT bin.

Conclusions/Observations

All algorithms have significantly cleaner looking pi0 peaks.  MC data will need to be analyzed to determine whether we really have improved the pi0 purity, or whether we have just sculpted the background to look more like the peak.  Suprisingly, after all these cuts to clean things up, the TSP algorithm actually has the highest statistics.