As we’ve talked about, there’s a strange effect in the soft electron eta distribution, with edges at about +/- 0.5 that make it look like a muon distribution:

I’ve found out what the problem is: the CES response is different at different points in CesZ.  Pasha’s 2D CES calibrations normalized the E_CES / P response to real electrons with respect to position, but the fakes have a different profile:

I neglected this correlation between E_CES and Z_CES in the likelihood, so we end up with more mistags (because more pions have a high E_CES) at low eta and fewer mistags at high eta, which is consistent with the distribution that we saw.  I could retrain the likelihood to take this correlation into account, or just modify my MC parameterizations to try to make them agree with the data.  The latter would take less time, so I’ll work on that now, but we really should actually fix it (and retrain the likelihood again) someday.

Edit: (7/7/10)

There’s another effect which also contributes:  the fakes have a larger spread of their CES Delta Z when the tracks are at a higher eta:

Again, the CES calibrations normalized this for real electrons, not for fakes.  This is another effect that gives fewer mistags at high eta.

-Scott