Testing CPT invariance by using C-even neutral-meson--antimeson   correlated states
  We consider the decays of a correlated neutral-meson--antimeson state with C-parity +1. We show that there is CPT noninvariance in the mixing of the neutral mesons if, for any two decay modes f and g, the decay rate has a component R_A which is antisymmetric under the interchange of the decay times t_1 and t_2. In particular, one may cleanly extract the CPT-noninvariance parameter with the help of R_A by using opposite-sign dilepton events. 
G.V. Dass, W. Grimus, L. Lavoura