  With the time dependant CP asymmetry in $B_d(t) \to \psi K_S$ well measured,
the most powerful method to search for {\em direct} CP violation in $B_d$
decays is to analyze whether the CP asymmetry of other transitions like $B_d(t)
\to \pi ^+ \pi ^-, \eta ^{\prime}K_S$ etc. can be described by a $sin$ term
taken from $B_d(t) \to \psi K_S$ and without a cos term. The failure of such a
constrained fit would establish direct CP violation (even if no CP asymmetry
were observed in these other modes).
