Contribution of $Z_b$ resonances to $\mathrm{{\rm Y}}(5S)\to \pi \pi \pi {\chi }_b$

We discuss the recently presented Belle results on the decays $\Upsilon(5S) \to \pi \pi \pi \chi_{bJ}(1P)$\mathrm{.}Thedataindicatethatinadditiontothe$\omega$emission,$\Upsilon(5S) \to \omega \chi_{bJ}$, there is a significant non resonant background in the three pion spectrum. We suggest that a sizable fraction of this background may be associated with the cascade process $\mathrm{{\rm Y}}(5S)\to \pi Z_b\to \pi \rho {\chi }_b$ involving the $Z_b(10610)$ and $Z_b(10650)$ resonances. If confirmed by the data, this would be the first observation of transition from the $Z_b$ resonances to lower bottomonium with emission of a light meson state different from a single pion, which may provide a new input in understanding of the internal dynamics of these resonances.