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We analyze the Belle data [K. F. Chen {\it et al.} (Belle Collaboration),Phys.\ Rev.\ Lett.\ {\bf 100}, 112001 (2008); I. Adachi {\it et al.} (BelleCollaboration), arXiv:0808.2445] on the processes $e^+ e^- \to \Upsilon(1S)\;\pi^+\pi^-, \Upsilon(2S)\; \pi^+\pi^-$ near the peak of the $\Upsilon(5S)$resonance, which are found to be anomalously large in rates compared to similardipion transitions between the lower $\Upsilon$ resonances. Assuming thesefinal states arise from the production and decays of the $J^{PC}=1^{--}$ state$Y_b(10890)$, which we interpret as a bound (diquark-antidiquark) tetraquarkstate $[bq][\bar{b}\bar{q}]$, a dynamical model for the decays $Y_b \to\Upsilon(1S)\; \pi^+\pi^-, \Upsilon(2S)\; \pi^+\pi^-$ is presented. Dependingon the phase space, these decays receive significant contributions from thescalar $0^{++}$ states, $f_0(600)$ and $f_0(980)$, and from the $2^{++}$$q\bar{q}$-meson $f_2(1270)$. Our model provides excellent fits for the decaydistributions, supporting $Y_b$ as a tetraquark state.

Tetraquark interpretation of the BELLE data on the anomalous  $\Upsilon(1S) \pi^+\pi^-$ and $\Upsilon(2S) \pi^+\pi^-$ production near the  $\Upsilon(5S)$ resonance