Measuring Top Quark Polarization in Top Pair plus Missing Energy Events
  The polarization of a top quark can be sensitive to new physics beyond the standard model. Since the charged lepton from top quark decay is maximally correlated with the top quark spin, it is common to measure the polarization from the distribution in the angle between the charged lepton and the top quark directions. We propose a novel method based on the charged lepton energy fraction and illustrate the method with a detailed simulation of top quark pairs produced in supersymmetric top squark pair production. We show that the lepton energy ratio distribution that we define is very sensitive to the top quark polarization but insensitive to the precise measurement of the top quark energy. 
Edmond L. Berger, Qing-Hong Cao, Jiang-Hao Yu, Hao Zhang
hep-ph hep-ex