Study of $\eta$ and dipion transitions in ${\rm Y}(4S)$ decays to lower bottomonia

Abstract

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

11 pages, 7 figures, 6 tables. Submitted to PRD

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• Charmonium
• Observation of anomalous Upsilon(1S)pi+pi- and Upsilon(2S)pi+pi- production near the Upsilon(5S) resonance
• Amplitude analysis of e+e- => Y(nS)pi+pi- at sqrt(s)=10.865 GeV
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• Two-pion transitions in quarkonium revisited
• Measurement of the branching fraction for the decay Upsilon(4S) -> Upsilon(1S)pi+pi-
• Single eta production in heavy quarkonia: breakdown of multipole expansion

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• Study of ${\chi }_{bJ}(2P)\to \omega {\rm Y}(1S)$ at Belle
• Hidden-bottom hadronic decays of ${\rm Y}(10753)$ with a ${\eta }^{(\prime )}$ or $\omega$ emission