Inspired by the newly observed two charged bottomoniumlike states, we consider the possible contribution from the intermediate $Z_b(10610)$ and $Z_b(10650)$ states to the ${\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-}$ decay process, which naturally explains Belle’s previous observation of the anomalous ${\rm Y}(2S){\pi }^{+}{\pi }^{-}$ production near the peak of ${\rm Y}(5S)$ at $\sqrt{s}=10.87\mathrm{GeV}$ [K. F. Chen et al. (Belle Collaboration), Phys. Rev. Lett. 100, 112001 (2008)]. The resulting $d\Gamma ({\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-})/d{m}_{{\pi }^{+}{\pi }^{-}}$ and $d\Gamma ({\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-})/d\cos \theta$ distributions agree with Belle’s measurement after inclusion of these $Z_b$ states. This formalism also reproduces the Belle observation of the double-peak structure and its reflection in the ${\rm Y}(2S){\pi }^{+}$ invariant mass spectrum of the ${\rm Y}(5S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-}$ decay.

• Received 26 May 2011

DOI:https://doi.org/10.1103/PhysRevD.84.074016