Charged bottomonium-like states $Z_b(10610)$ and $Z_b(10650)$ and the $Υ(5S)\to Υ(2S)π^+π^-$ decay

Abstract

Inspired by the newly observed two charged bottomonium-like states, we consider the possible contribution from the intermediate $Z_b(10610)$ and $Z_b(10650)$ states to the $Υ(5S)\to Υ(2S)π^+π^-$ decay process, which naturally explains Belle's previous observation of the anomalous $Υ(2S)π^+π^-$ production near the peak of $Υ(5S)$ at $\sqrt s=10.87$ GeV [K.F. Chen {\it et al}. (Belle Collaboration), Phys. Rev. Lett. {\bf 100}, 112001 (2008)]. The resulting $dΓ(Υ(5S)\to Υ(2S)π^+π^-)/dm_{π^+π^-}$ and $dΓ(Υ(5S)\to Υ(2S)π^+π^-)/d\cosθ$ 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 $Υ(2S)π^+$ invariant mass spectrum of $Υ(5S)\to Υ(2S)π^+π^-$ decay.

5 pages, 5 figures, 4 tables. More contents and discussions added