Strong Evidence for ZZ Production in p anti-p Collisions at s**(1/2) = 1.96 TeV

We report the first evidence of Z boson pair production at a hadron collider with a significance exceeding 4 standard deviations. This result is based on a data sample corresponding to 1.9fb-1 of integrated luminosity from pp̄ collisions at s=1.96TeV collected with the Collider Detector at Fermilab II detector. In the ′ ′ channel, we observe three ZZ candidates with an expected background of 0.096-0.063+0.092 events. In the νν channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of ′ ′ and νν channels, we observe an excess of events with a probability of 5.1×10-6 to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is σ(pp̄→ZZ)=1.4-0.6+0.7(stat+syst)pb, consistent with the standard model expectation