Observation of γ production in hadronic Z0 decays

Evindence for the production of Y mesons in hadronic Z0 decays is presented. Using a sample of 3.7 million hadronic events, eight Y candidates are identified from their decays into e+e− and μ+μ− pairs. The estimated background in the signal region is 1.6 ± 0.3 events. Based on existing theoretical models for inclusive Y production, the following branching ratio, summed over the three lightest Y states, is obtained: Br(Z0 → Y + X) = (1.0 ± 0.4 ± 0.1 ± 0.2) × 10−4 where the first error is statistical, the second systematic and the third error accounts for uncertainties in the production mechanism.