First Measurement of ZZ Production in ppbar Collisions at sqrt(s)=1.96 TeV

We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb-1 of integrated luminosity from p(bar p) collisions at √s = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the (ell)(ell)(ell)(prime)(ell)(prime) channel, we observe three ZZ candidates with an expected background of 0.096-0.063+0.092 events. In the (ell)(ell)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 (ell)(ell)(ell)(prime)(ell)(prime) and (ell)(ell)νν channels, we observe an excess of events with a probability of 5.1 x 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(p(bar p) →ZZ) = 1.4-0.6+0.7 (stat.+syst.) pb, consistent with the standard model expectation