  The three body decays $B \to D^{(*)} \bar{D}^{(*)} K_s$ may be used to
measure both $\sin{2\beta}$ and $\cos{2\beta}$. Crucial to the $\cos{2\beta}$
measurement is the resonant contribution to the three body decay from p-wave
excited $D_s$ states. If these p-wave states are the newly discovered
$D_s(2317)$ and $D_s(2460)$ then they are below the $D^{(*)} K$ threshold and
hence do not contribute to $B \to D^{(*)} \bar{D}^{(*)} K_s$. The three body
decays can then be used to measure $\sin{2\beta}$ without resonant dilution and
to look for new physics in $ b \to c \bar{c} s $ transition.
