Contribution of $Z_b$ resonances to $\Upsilon(5S) \to \pi \pi \pi \chi_b$

Abstract

We discuss the recently presented Belle results on the decays $\Upsilon(5S) \to \pi \pi \pi \chi_{bJ}(1P)$. The data indicate that in addition to the $\omega$ 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 $\Upsilon(5S) \to \pi Z_b \to \pi \rho \chi_b$ 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.