Observation of the decay Ds+ → η'π+

Using the ARGUS detector at the e + e - storage ring DORIS II at DESY, we have observed the decay D s + → η'π + in two decay modes of the η'. We measure the ratio of branching ratios BR(D s + → η'π + )/BR(D s + → Oπ + ) to be 2.5±0.5±0.3.