We report the observation of two narrow structures in the mass spectra of the ${\pi }^{\pm }{\rm Y}(nS)$ ($n=1$, 2, 3) and ${\pi }^{\pm }{h}_b(mP)$ ($m=1$, 2) pairs that are produced in association with a single charged pion in ${\rm Y}(5S)$ decays. The measured masses and widths of the two structures averaged over the five final states are $M_1=(10607.2\pm 2.0)\mathrm{MeV}/c^2$, ${\Gamma }_1=(18.4\pm 2.4)\mathrm{MeV}$, and $M_2=(10652.2\pm 1.5)\mathrm{MeV}/c^2$, ${\Gamma }_2=(11.5\pm 2.2)\mathrm{MeV}$. The results are obtained with a $121.4{\mathrm{fb}}^{-1}$ data sample collected with the Belle detector in the vicinity of the ${\rm Y}(5S)$ resonance at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

• Received 12 October 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.122001