== W and H+ polarizations in top decays  ==
   1. Generate $e^+e^-  \to t \bar t$ at threshold and force the tops to decay leptonically (to $e$ or $\mu$).
      a. Compare the charged and neutral lepton $p_T$ (or energy) distributions with those shown in the MC lectures.
      a. Explain why the neutrinos tend to have higher $p_T$ than the charged leptons. 
      a. How would things change if the decay went via $t\to b H^+$ with $m_{H^+}=m_W$? Check by using
          the 2HDM (Use the on-line calculator to get a consistent set of parameters for the 2HDM).
   1. As the previous exercise, but in  $pp \to t\bar t$ at the LHC. 


-- Main.FabioMaltoni - 06 Dec 2008