Abstract:
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 1.9 fb-1 of integrated luminosity from $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV collected with the Collider Detector at Fermilab II detector. In the [script-l][script-l][script-l][prime][script-l][prime] channel, we observe three ZZ candidates with an expected background of 0.096-0.063+0.092 events. In the [script-l][script-l]nunu 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 [script-l][script-l][script-l][prime][script-l][prime] and [script-l][script-l]nunu 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 sigma($p\bar{p}$-->ZZ)=1.4-0.6+0.7(stat+syst) pb, consistent with the standard model expectation.
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