Study of e + e − → Υ ( 1 S , 2 S ) η and e + e − → Υ ( 1 S ) η ′ at √ s = 10.866 GeV with the Belle detector

Abstract

We report the first observation of the processes eþe− → ϒð1S; 2SÞη at ffiffi s p ¼ 10.866 GeV, with significance exceeding 10σ for both processes. The measured Born cross sections are σðeþe− → ϒð2SÞηÞ ¼ 2.07 0.21 0.19 pb, and σðeþe− → ϒð1SÞηÞ ¼ 0.42 0.08 0.04 pb. We also set the upper limit on the cross section of the process eþe− → ϒð1SÞη0 to be σðeþe− → ϒð1SÞη0 Þ < 0.037 pb at 90% C.L. The results are obtained with the data sample collected with the Belle detector at the KEKB asymmetric-energy eþe− collider in the energy range from 10.63 to 11.02 GeV