Measurement of the Mass Difference Between Top and Anti-top Quarks at   CDF
  We present a measurement of the mass difference between top ($t$) and anti-top ($\bar{t}$) quarks using $t\bar{t}$ candidate events reconstructed in the final state with one lepton and multiple jets. We use the full data set of Tevatron $\sqrt{s} = 1.96$ TeV proton-antiproton collisions recorded by the CDF II detector, corresponding to an integrated luminosity of 8.7 fb$^{-1}$. We estimate event-by-event the mass difference to construct templates for top-quark signal events and background events. The resulting mass difference distribution of data compared to signal and background templates using a likelihood fit yields $\Delta M_{top} = {M}_{t} - {M}_{\bar{t}} = -1.95 $pm$ 1.11 (stat) $pm$ 0.59 (syst)$ and is in agreement with the standard model prediction of no mass difference. 
T. Aaltonen, B. Alvarez Gonzalez, S. Amerio, D. Amidei, A. Anastassov,   A. Annovi, J. Antos, G. Apollinari, J. A. Appel, A....
hep-ex