First observation of exclusive $\mathrm{{\rm Y}}(1S)$ and $\mathrm{{\rm Y}}(2S)$ decays into light hadrons

Using samples of 102 million $\mathrm{{\rm Y}}(1S)$ and 158 million $\mathrm{{\rm Y}}(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to the three-body final states $\varphi K^{+}{K}^{-}$, $\omega {\pi }^{+}{\pi }^{-}$ and $K^{\ast 0}(892)K^{-}{\pi }^{+}$, and to the two-body Vector-Tensor ($\varphi f_2^{\mathrm{\prime }}(1525)$, $\omega f_2(1270)$, $\rho a_2(1320)$ and $K^{\ast 0}(892){\bar{K}}_2^{\ast 0}(1430)$) and Axial-vector-Pseudoscalar ($K_1(1270{)}^{+}{K}^{-}$, $K_1(1400{)}^{+}{K}^{-}$ and $b_1(1235{)}^{+}{\pi }^{-}$) pairs. Signals are observed for the first time in the $\mathrm{{\rm Y}}(1S)\to \varphi K^{+}{K}^{-}$, $\omega \pi^+ \pi^-$,$K^{\ast 0} K^- \pi^+$,$K^{\ast0} K_2^{\ast 0}$and$\Upsilon(2S) \to \phi K^+ K^-$,$K^{\ast 0} K^- \pi^+$ decay modes. Branching fractions are determined for all the processes, while 90% confidence level upper limits are established on the branching fractions for the modes with a statistical significance less than $3\sigma$. The ratios of the branching fractions of $\mathrm{{\rm Y}}(2S)$ and $\mathrm{{\rm Y}}(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI suppressed bottomonium decays.