Observation of Υ(4S)→η′Υ(1S

Abstract

We report the first observation of the hadronic transition Υ(4S)→η′Υ(1S), using 496 fb−1 data collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We reconstruct the η′ meson through its decays to ρ0γ and to π+π−η, with η→γγ. We measure B(Υ(4S)→η′Υ(1S))=[3.43±0.88(stat)±0.21(syst)]×10−5, with a significance of 5.7σ.