KS IS A PI-PI-RESONANCE

We present the quantum mechanically honest description of unstable particles. We demonstrate it by taking the short-lived neutral K-meson K(S) as an example. K(s) can be described properly as a pi-pi-resonance. This view will be explicitly shown based upon a toy model which allows exact stationary pi-pi-scattering solutions at any fixed energy. All our results can easily be extended to cases of realistic unstable particles. Notably it will be shown that the weak interactions responsible to particle decays are dominating at resonances (decaying particles), where strong interactions play minor roles (and are regarded as small perturbation terms there). In other words, weak interactions exhibit non-perturbative effects at resonance regions.