Testing the Wigner - Weisskopf approximation by using neutral-meson - antimeson correlated states

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We phenomenologically decompose the Weisskopf--Wigner approximation, as applied to the neutral flavoured meson complexes, into three pieces and propose tests for these pieces. Our tests hold for general decay amplitudes and M⁰-- M⁰ mixing parameters. We concentrate on C-odd M⁰ M⁰ states and stress the importance of such tests in view of the variety of physics extracted from measurements on such complexes. Studying the feasibility of the tests confines one to the K⁰ K⁰ system at present. In particular, we show that the time dependence of the correlated decay ϕ→ K⁰ K⁰ → 2 (π+ π-) is determined solely by the WWA and provides thus a clean test of it.