Measurement of the production rates of η and η′ in hadronic Z decays

The decays η → γγ and η′ → ηπ + π − have been observed in hadronic decays of the Z produced at LEP. The fragmentation functions of both the η and η′ have been measured. The measured multiplicities for x > 0.1 are 0.298±0.023±0.021 and 0.068±0.016 for η and η′ respectively. While the fragmentation function for the η is fairly well described by the JETSET Monte Carlo, it is found that the production rate of the η′ is a factor of four less than the corresponding prediction.