Energy scan of the $e^{+}{e}^{-}\to h_b(nP){\pi }^{+}{\pi }^{-}$ $(n=1,2)$ cross sections and evidence for $\mathrm{{\rm Y}}(11020)$ decays into charged bottomonium-like states

Using data collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, we measure the energy dependence of the $e^+e^- \to h_b(nP)\pi^+\pi^-$ $(n=1,2)$ cross sections from thresholds up to $11.02$GeV. We find clear $\mathrm{{\rm Y}}(10860)$ and $\mathrm{{\rm Y}}(11020)$ peaks with little or no continuum contribution. We study the resonant substructure of the $\mathrm{{\rm Y}}(11020)\to h_b(nP){\pi }^{+}{\pi }^{-}$ transitions and find evidence that they proceed entirely via the intermediate isovector states $Z_b(10610)$ and $Z_b(10650)$. The relative fraction of these states is loosely constrained by the current data: the hypothesis that only $Z_b(10610)$ is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only $Z_b(10650)$ is produced is not excluded at a significant level.