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The $\eta$ production in the $(n,n')$ bottomonium transitions $\Upsilon (n)\to \Upsilon (n') \eta, $ is studied in the method used before for dipion heavyquarkonia transitions. The widths $\Gamma_\eta(n,n')$ are calculated withoutfitting parameters for $n=2,3,4,5, n'=1$.Resulting $\Gamma_\eta(4,1)$ is foundto be large in agreement with recent data.

Single eta production in heavy quarkonia transitions