We study hadronic transitions between bottomonium states using $496{\mathrm{fb}}^{-1}$ data collected at the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^{+}{e}^{-}$ collider. We measure $\mathcal{B}(\mathrm{\Upsilon }(4S)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(1S))=(8.2\pm 0.5(\text{stat})\pm 0.4(\text{syst}))\times {10}^{-5}$, $\mathcal{B}(\mathrm{\Upsilon }(4S)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(2S))=(7.9\pm 1.0(\text{stat})\pm 0.4(\text{syst}))\times {10}^{-5}$, and $\mathcal{B}(\mathrm{\Upsilon }(4S)\to \eta \mathrm{\Upsilon }(1S))=(1.70\pm 0.23(\text{stat})\pm 0.08(\text{syst}))\times {10}^{-4}$. We measure the ratio of branching fractions $\mathcal{R}=\mathcal{B}(\mathrm{\Upsilon }(4S)\to \eta \mathrm{\Upsilon }(1S))/\mathcal{B}(\mathrm{\Upsilon }(4S)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(1S))=2.07\pm 0.30(\text{stat})\pm 0.11(\text{syst})$. We search for the decay $\mathrm{\Upsilon }(1{{}^{3}D}_{1,2})\to \eta \mathrm{\Upsilon }(1S)$, but do not find significant evidence for such a transition. We also measure the initial-state radiation production cross sections of the $\mathrm{\Upsilon }(2S,3S)$ resonances and we find values compatible with the expected ones. Finally, the analysis of the $\mathrm{\Upsilon }(4S)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(1S)$ events shows indications for a resonant contribution due to the $f_0(980)$ meson.

• Received 16 July 2017

DOI:https://doi.org/10.1103/PhysRevD.96.052005