Mixing model for bottomoniumlike Zb resonances

The isovector bottomoniumlike exotic resonances Zb(10610) and Zb(10650) are very close to the thresholds of heavy meson pairs BB∗(BB∗) and B∗B∗, and are naturally understood as "molecular" states made of the corresponding meson-antimeson pairs. The picture with a full separation of the two channels cannot be exact and a cross-feed between the states necessarily takes place. A simple model is considered here describing the mixing between the channels in terms of one parameter. The model reasonably describes the current data on the decays of the Zb resonances to bottomonium plus a pion and predicts the rate and a distinctive interference pattern for the decay Zb(10650)→BB∗(BB∗) as well as excess of the mass splitting between the resonances over the mass difference between B∗ and B mesons.