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 Υ(4S) resonance with the Belle detector at the KEKB asymmetric energy e+e− collider. We measure: (Υ(4S)→π+π−Υ(1S))=(8.2±0.5(stat.)±0.4(syst.))×10−5, (Υ(4S)→π+π−Υ(2S))=(7.9±1.0(stat.)±0.4(syst.))×10−5, and (Υ(4S)→ηΥ(1S))=(1.70±0.23(stat.)±0.08(syst.))×10−4. We measure the ratio of branching fractions =(Υ(4S)→ηΥ(1S))/(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.