Consequences of heavy-quark symmetries for hadronic molecules

Abstract

Among the newly observed structures in the heavy-quarkonium mass region, some have been proposed to be hadronic molecules. We investigate the consequences of heavy-quark flavor symmetry on these heavy meson hadronic molecules. The symmetry allows us to predict new hadronic molecules on one hand, and test the hadronic molecular assumption of the observed structures on the other hand. We explore the consequences of the flavor symmetry assuming the $X(3872)$ and ${Z}_{b}(10\text{ }610)$ as an isoscalar $D{\overline{D}}^{*}$ and isovector $B{\overline{B}}^{*}$ hadronic molecule, respectively. A series of hadronic molecules composed of heavy mesons are predicted. In particular, there is an isoscalar ${1}^{++}$ $B{\overline{B}}^{*}$ bound state with a mass about 10 580 MeV which may be searched for in the $\ensuremath{\Upsilon}(1S,2S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ mass distribution; the isovector charmonium partners of the ${Z}_{b}(10\text{ }610)$ and the ${Z}_{b}(10\text{ }650)$ are also predicted, which probably corresponds to the very recently observed ${Z}_{c}(3900)$ and ${Z}_{c}(4025)$ resonances by the BESIII Collaboration.