I've been looking at Z events in the W sample.  

The following cuts are applied:

  ZMk->setNearEtFrac(0.25); -- At least 25% of the total nearside ET (defined as in the W analysis) must be in the 2x2 cluster.  This cut is wide open.

  ZMk->setClusterMinEt(25); -- The 2x2 cluster ET must be at least 25GeV.

  ZMk->set4x4fmax(0.90); -- At least 90% of the total 4x4 ET must be in the 2x2 cluster.

  ZMk->setMinZMass(60); -- The invariant mass of the ee pair must be at least 60GeV

  ZMk->setMaxZMass(150); -- The invariant mass of the ee pair must be less than 150GeV

These cuts result in 16 Z events in the sample (though some fraction of the runs failed during processing and I never went back to catch them).  Unfortunately, afs is not cooperating, so I can't attach the pdf that shows the event displays for each Z candidate, but I will add it as soon as I can.  In the meantime:

The invariant mass peak with these simple cuts is already (pretty much) where it should be.

It's not perfect, but the majority of the events have one electron and one positron.  The outlying events may have track pts that are very large (and hence hard to differentiate between + and -), but that will have to wait for a future update.