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

TL;DR

This paper reports the first measurement of ZZ boson pair production cross section in proton-antiproton collisions at 1.96 TeV, using data from the Fermilab Tevatron, confirming the standard model prediction with a 4.4 sigma significance.

Contribution

It provides the first experimental measurement of ZZ production cross section at a hadron collider, validating standard model predictions.

Findings

Measured cross section: 1.4^{+0.7}_{-0.6} pb

Observed significance: 4.4 standard deviations

Consistent with standard model expectations

Abstract

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 ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the llll channel, we observe three ZZ candidates with an expected background of 0.096^{+0.092}_{-0.063} events. In the llnunu 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 llll and llnunu channels, we observe an excess of events with a probability of $5.1\times 10^{-6}$ to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is sigma(ppbar -> ZZ) = 1.4^{+0.7}_{-0.6} (stat.+syst.) pb, consistent with the standard model expectation.