Study of <i>e</i><SUP>+</SUP><i>e</i><SUP>-</SUP> → Υ(1S, 2S)η and <i>e</i><SUP>+</SUP><i>e</i><SUP>-</SUP> → Υ(1<i>S</i>)η′ at √<i>s</i>=10.866 GeV with the Belle detector

Abstract

We report the first observation of the processes e(+)e(-) -> Upsilon(1S, 2S)eta at root s = 10.866 GeV, with significance exceeding 10 sigma for both processes. The measured Born cross sections are sigma(e(+)e(-) -> Upsilon(2S)eta) = 2.07 +/- 0.21 +/- 0.19 pb, and sigma(e(+)e(-) -> Upsilon(1S)eta) = 0.42 +/- 0.08 +/- 0.04 pb. We also set the upper limit on the cross section of the process e(+)e(-) -> Upsilon(1S)eta to be sigma(e(+)e(-) -> Upsilon(1S)eta') < 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 e(+)e(-) collider in the energy range from 10.63 to 11.02 GeV.