Study of η and dipion transitions in Υ(4 S) decays to lower bottomonia

Abstract

We study hadronic transitions between bottomonium states using 496 fb−1 data collected at the Υ(4S)resonance with the Belle detector at the KEKB asymmetric energy e+e− collider. We measure B(Υ(4S)→π+π−Υ(1S))=(8.2±0.5(stat)±0.4(syst))×10−5, B(Υ(4S)→π+π−Υ(2S))=(7.9±1.0(stat)±0.4(syst))×10−5, and B(Υ(4S)→ηΥ(1S))=(1.70±0.23(stat)±0.08(syst))×10−4. We measure the ratio of branching fractions R=B(Υ(4S)→ηΥ(1S))/B(Υ(4S)→π+π−Υ(1S))=2.07±0.30(stat)±0.11(syst). We search for the decay Υ(13D1,2)→ηΥ(1S), but do not find significant evidence for such a transition. We also measure the initial-state radiation production cross sections of the Υ(2S,3S) resonances and we find values compatible with the expected ones. Finally, the analysis of the Υ(4S)→π+π−Υ(1S)events shows indications for a resonant contribution due to the f0(980) meson

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