Observation of Υ(2S)→ηΥ(1S) and Search for Related Transitions BriereRoy A. FergusonThomas TatishviliG. VogelHelmut WatkinsM. E. CollaborationCLEO 2008 <p>We report the first observation of Υ(2S)→ηΥ(1S), with a branching fraction B=(2.1<sub>-0.6</sub><sup>+0.7</sup>(stat)±0.3(syst))×10<sup>-4</sup> and a statistical significance 5.3σ. Data were acquired with the CLEO III detector at the CESR e<sup>+</sup>e<sup>-</sup> symmetric collider. This is the first process observed involving a b-quark spin flip. For related transitions, 90% confidence limits in units of 10<sup>-4</sup> are B(Υ(2S)→π<sup>0</sup>Υ(1S))0Υ(1S))0Υ(2S))<5.1.</p>