Observation Of Y Production In Hadronic Z(0) Decays

Evidence for the production of Upsilon mesons in hadronic Z(0) decays is presented. Using a sample of 3.7 million hadronic events, eight Upsilon candidates are identified from their decays into e(+)e(-) and mu(+)mu(-) pairs. The estimated background in the signal region is 1.6 +/- 0.3 events. Based on existing theoretical models for inclusive Upsilon production, the following branching ratio, summed over the three lightest Upsilon states, is obtained:Br(Z(0) --> Upsilon + X) = (1.0 +/- 0.4 +/- 0.1 +/- 0.2) x 10(-4),where the first error is statistical, the second systematic and the third error accounts for uncertainties in the production mechanism.