Improving the mass plots

When checking the performance of the precuts we found that the jet mass cut was cutting very little of the ZZ background out; there should be similar numbers of ZH and ZZ going into the likelihood cut but we had about 4 times as much ZZ. The mass plot (here, for cheated electron identification) is quite wide and has a long high tail on the ZZ.
We had a look at several things, like trying ycut jet finding in case it was initial state radiation photons being lumped in as well when forcing to 2 jets. Nothing conclusive came up so I looked directly at a few events with the di-jet mass over 200 GeV. They all seemed to have highly energetic photons from the Z (the one that goes to electrons) or from the electrons themselves lumped into the jets. I had a go at cutting out any photons (as identified by Pandora) that are within 4 degrees of the primary electrons and came up with this. Here's a plot of the energy and number of these photons.
After checking that I thought I'd try and find out if there was anything else being thrown in that shouldn't. From the Monte Carlo to reconstructed particle relations I listed all the reconstructed particles that come from each Z (for ZZ; or Z and H for ZH) separately and plotted the invariant mass for these. That's basically the best you could ever get without improving the particle flow/tracking/etcetera. Here's a plot of the 3 methods over laid for the ZZ sample - original cheated electron ID; bremsstrahlung removed and completely cheated jet association. Removing the bremsstrahlung photons does a pretty good job, but there's still something going into the jets that shouldn't. Here's some details about the particles that are left over when assigning to the Z or the H (or the Zs for the ZZ sample) from Monte Carlo.

Next steps:

• Find out what these left over particles are.
• See how the mass plots look using realistic electron finding and removing the bremsstrahlung.
• See how many ZZ and ZH get through the precuts now.