Search for New Physics in $D^\pm \to K_S X^{\pm} $ and $D^\pm \to K_S   K_S K^{\pm}$
  Direct CP violation beyond the standard model can be produced in charged D decays to final states with a $K_S$ by small new physics contributions to the transitions $D^+ \to K^o X^+$, where $X^+$ denotes any positively charged hadronic state or transitions $D^+ \to K^o \bar K^o K^{(*)+}$, where $K^{(*)+}$ denotes any positive strange state. These transitions are doubly-Cabibbo suppressed and color suppresed in the standard model and branching ratios are experimentally observed to be suppressed by two orders of magnitude relative to the allowed $D^+ \to \bar K^o X^+$ or $D^+ \to \bar K^o \bar K^o K^{(*)+}$, branching ratio. An even smaller new physics contribution might produce an observable CP asymmetry in $D^\pm \to K_S X^\pm$ or $D^{\pm} \to K_S K_S K^{(*)\pm}$ decays. Since such asymmetries are easily checked in the early stages of any charm production experiment, it seems worth while to check them before the opportunity is lost in later stages of the analysis, even if no theoretical model predicts such an asymmetry. 
Harry J. Lipkin (Weizmann Institute of Science, Tel Aviv University   and Argonne National Laboratory)