Spin Correlations in Top Quark Production and the Top Quark Mass
  Top-antitop quark pairs produced at the Tevatron have a sizeable spin correlation. That correlation feeds into the angular distribution of the decay products, particularly in the dilepton channel. Including the expected correlation in an overall analysis of a handful of actual dilepton events continues to favor a lower top mass (centered on 155 GeV) than the single lepton events. 
Gary R. Goldstein (Tufts University)