Distributions from ensemble tests conducted on the Pythia ttbar MC
samples generated with (mt,mtb)=(170,165)GeV consisting of 1000 pseudo
experiments with data-like composition (Pythia ttbar with  + Alpgen
W+jets).  The histograms from left to right are: (a) expected
uncertainty of the extracted mass difference, (b) extracted mass
difference (c) pull for the extracted mass difference.  Only the
distributions for the e+jets channel are shown.