A fresh look at neutral meson mixing

In this work we show that the existence of a complete biorthonormal set of eigenvectors of the effective Hamiltonian governing the time evolution of neutral meson system is a necessary condition for diagonalizability of such a Hamiltonian. We also study the possibility of probing the CPT invariance by observing the time dependence of cascade decays of type P○(P¯○)→{Ma,Mb}X→fX by employing such basis and exactly determine the CPT violation parameter by comparing the time dependence of the cascade decays of tagged P○ and tagged P¯○.