CP Violating Effects in $e^+e^-\rightarrow ZH$ and Their Optimization
  We consider the possibilities of testing CP conservation in the process $e^+e^- \rightarrow ZH$. The easiest is to measure the forward-backward asymmetry of the $Z$ boson, a nonzero value of which signals CP violation. The effects of CP violation are predicted in the two Higgs doublet model. We show here that a choise of optimal observables can improve the possibility of observing CP violation. Although the number of events is not large, useful information about CP violating parameters can be extracted. 
J.P. Ma & B.H.J. McKellar