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

Abstract

We study hadronic transitions between bottomonium states using 496 fb-1 data collected at the ?(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e-collider. We measure B(?(4S)→π+π(1S))=(8.2±0.5(stat)±0.4(syst))×10-5, B(?(4S)→π+π(2S))=(7.9±1.0(stat)±0.4(syst))×10-5, and B(?(4S)→η?(1S))=(1.70±0.23(stat)±0.08(syst))×10-4. We measure the ratio of branching fractions R=B(?(4S)→η?(1S))/B(?(4S)→π+π(1S))=2.07±0.30(stat)±0.11(syst). We search for the decay ?(1D31,2)→η?(1S), but do not find significant evidence for such a transition. We also measure the initial-state radiation production cross sections of the ?(2S,3S) resonances and we find values compatible with the expected ones. Finally, the analysis of the ?(4S)→π+π(1S) events shows indications for a resonant contribution due to the f0(980) meson.