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

Abstract

Using samples of 102 million ${\rm Y}(1S)$ and 158 million ${\rm Y}(2S)$ 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 ($\varphi f_2^{\prime }(1525)$, $\omega f_2(1270)$, $\rho a_2(1320)$ 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 ${\rm Y}(1S)\to \varphi K^{+}{K}^{-}$, $\omega {\pi }^{+}{\pi }^{-}$, $K^{\ast 0}{K}^{-}{\pi }^{+}$, $K^{\ast 0}{K}_2^{\ast 0}$ and ${\rm Y}(2S)\to \varphi K^{+}{K}^{-}$, $K^{\ast 0}{K}^{-}{\pi }^{+}$ 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 ${\rm Y}(2S)$ and ${\rm Y}(1S)$ decays into the same final state are used to test a perturbative QCD prediction for OZI suppressed bottomonium decays.

Comments: 7 pages, 5 figures, 1 table, accepted for publication as a Rapid Communication in Physical Review D