First observation of exclusive $Υ(1S)$ and $Υ(2S)$ decays into light hadrons

Using samples of 102 million $Υ(1S)$ and 158 million $Υ(2S)$ events collected with the Belle detector, we study exclusive hadronic decays of these two bottomonium resonances to the three-body final states $ϕK^+ K^-$, $ωπ^+ π^-$ and $K^{\ast 0}(892) K^- π^+$, and to the two-body Vector-Tensor ($ϕf_2'(1525)$, $ωf_2(1270)$, $ρa_2(1320)$ and $K^{\ast 0}(892) \bar{K}_2^{\ast 0}(1430)$) and Axial-vector-Pseudoscalar ($K_1(1270)^+ K^-$, $K_1(1400)^+ K^-$ and $b_1(1235)^+ π^-$) pairs. Signals are observed for the first time in the $Υ(1S) \to ϕK^+ K^-$, $ωπ^+ π^-$, $K^{\ast 0} K^- π^+$, $K^{\ast0} K_2^{\ast 0}$ and $Υ(2S) \to ϕK^+ K^-$, $K^{\ast 0} K^- π^+$ 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 $3σ$. The ratios of the branching fractions of $Υ(2S)$ and $Υ(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI suppressed bottomonium decays.

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