Systematic study of the singularity mechanism in heavy quarkonium decays
Abstract
We investigate in detail the role of heavy meson loops in the transition from JPC=1-- sources to candidates for QCD "exotics", such as Zc(3900), Zb(10610) and Zb'(10650). We demonstrate that, if a vector state strongly couples to a heavy meson pair in an S--wave and this system decays to another heavy meson pair (e.g. via pion emission), again in an S-wave, the pertinent diagrams get enhanced significantly, if the intermediate states are (near) on--shell and have small relative momenta. In a limited kinematic range this mechanism generates "singularity regions" that lead to the creation of a large number of low energy heavy meson pairs, providing an ideal environment for the formation of hadron-hadron bound states or resonances. For instance, we predict that the signals for Zb and Zb' should be a lot stronger in (6S) decays due to this mechanism, if these states are indeed hadron-hadron resonances. The findings of this work should be valuable for deepening our understanding of the nature of the mentioned states.