This plot shows the mass peak for the Z' particle from the pythia simulation. As pile up increases there is a widening in the peak. The Z' is, in this simulation, forced to decay into two electrons. The reconstruction computes the invariant mass of the Z' using these two electrons. This makes this Simulation quite similar to the dielectron gun simulation. As was predicted, pile up effects the width of the peak by adding energy to the superclusters which are formed from the two electrons.
This is the histrogram from the pile up two case. There is a small peak close to zero that would suggest a percentage of events that are poorly reconstructed. This could happen when a supercluster from a pile up particle is used instead of one from an electron and thus the initial energy is much lower.
This is a plot of the distance between the two superclusters in phi. Due to the properties of the Z' the electrons should decay in opposite directions in phi. Because the distance fully around the detector in phi is two pi there should be a distance of pi in phi between the two electrons. This is the case here with a high number of electrons that are pi distance in phi apart.