Measurement of the ZZ Cross Section via the ZZ →4l Channel
Measuring heavy diboson characteristics in pp collisions is a way of probing the structure of the electroweak sector, and provides milestones on the way to sensitivity to rare processes such as Higgs boson production. The ZZ is the last diboson channel without a precision cross-section measurement.
We measure the ZZ cross-section in the four-lepton channel. We base our analysis heavily on the work done by a previous group at CDF. In addition to the increased statistics from a later iteration of the analysis, we also optimize our signal acceptance to reduce our cross-section error. The ZZ is a rare process and the highest sensitivity channel, in ZZ→llll, has a branching fraction of only 0.46%. In increasing our yield as much as possible while still controlling our background we attempt to bring the ZZ into the realm of precision Standard Model physics.
Using 6.1 fb-1 of data collected by the CDF experiment in pp collisions at 1.96 TeV we expected 10.4 signal events and 0.26 background events; we observed 14 ZZ → 4l candidate events (where l is a charged lepton). Which gives us a cross-section measurement of:
This agrees with the Standard Model prediction NLO cross-section of 1.4 pb at just over one sigma.