Systematic study of the singularity mechanism in heavy quarkonium decays

We investigate in detail the role of heavy meson loops in the transition from J(PC) = 1(--) sources to candidates for QCD exotics, such as Z(c)(3900), Z(b) (10610) and 4(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 Z(b) and Z(b)' should be a lot stronger in Y(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. (C) 2013 Elsevier B.V. All rights reserved.