The effect of multi-channel pion-pion scattering in decays of the Υ-family mesons

الأصل · EN

The effect of isoscalar S-wave multi-channel pion-pion scattering (ππ→ππ,KK,ηη) is considered in the analysis of data on decays of the Υ-meson family -- Υ(2S)→Υ(1S)ππ, Υ(3S)→Υ(1S)ππ and Υ(3S)→Υ(2S)ππ. The analysis, which aims at studying the scalar mesons, is performed jointly considering the multi-channel pion-pion scattering, which is described in our model-independent approach based on analyticity and unitarity and using an uniformizing variable method, and the charmonium decay processes J/ψ→ϕ(ππ, KK), ψ(2S)→ J/ψ(ππ). Results of the analysis confirm all our earlier conclusions on the scalar mesons. It is also shown that in the final states of the Υ-meson family decays (except for the ππ scattering) the contribution of the coupled processes, e.g., KK→ππ, is important even if these processes are energetically forbidden. This is in accordance with our previous conclusions on the wide resonances: If a wide resonance cannot decay into a channel which opens above its mass but the resonance is strongly connected with this channel (e.g. the f₀(500) and the K channel), one should consider this resonance as a multi-channel state with allowing for the indicated channel taking into account the Riemann-surface sheets related to the threshold branch-point of this channel and performing the combined analysis of the considered and coupled channels.