Title: CP violation in τ ± → π ± K S v and D ± → π ± K S : the importance of K S − K L interference
Abstract: The B-factories have measured CP asymmetries in the τ → πK S ν and D → K S π modes. The K S state is identified by its decay to two pions at a time that is close to the K S lifetime. Within the Standard Model and many of its extensions, the asymmetries in these modes come from CP violation in $ {K^0} - {\overline K^0} $ mixing. We emphasize that the interference between the amplitudes of intermediate K S and K L is as important as the pure K S amplitude. Consequently, the measured asymmetries depend on the times over which the relevant decay rates are integrated and on features of the experiment.