Single eta production in heavy quarkonia: Breakdown of multipole expansion

The η production in the (n,n') bottomonium transitions Y(n)→Y(n')η, is studied in the method used before for dipion heavy quarkonia transitions. The widths Γη(n,n') are calculated without fitting parameters for n=2,3,4,5, n'=1. Resulting Γη(4,1) is found to be large in agreement with recent data. Multipole expansion method is shown to be inadequate for large size systems considered