Two-Particle Correlations and Meson-Antimeson Mixing Effects

We discuss 2-particle correlations which arise in the time evolution of C-odd and C-even meson--antimeson states of flavoured neutral mesons. In order to keep our discussion general, we do not use the Weisskopf -- Wigner approximation. Possible deviations from quantum-mechanical coherence effects are parameterized by a so-called decoherence parameter $\zeta$. In particular, we study the $\zeta$-dependence of the asymmetry of unlike and like-flavoured events which was recently observed experimentally in the $K^0 \bar{K}^0$ system. In this $\zeta$-dependence, we point out some important general features which do not rely on the Weisskopf -- Wigner approximation. Some other related results are derived more generally than in the literature.