ZZ deals two pairs or four of a kind

Getting four of a kind is rare and exciting when playing poker and when examining events from DZero.

While being dealt four of a kind in poker is much more rare and memorable than getting two pairs, finding either is exciting in an event at DZero. The neutral Z boson, a weak force carrier, can decay into a pair of leptons, such as electrons or muons. This kind of decay is frequent enough that researchers use Z boson events to measure properties of the detector and calibrate it for use in other analyses. However, the simultaneous production of two Z bosons is very rare, only slightly more frequent than Higgs boson production. Sometimes both Z bosons will decay into electron or muon pairs, leading to very rare and striking events that could include four of the same kind of lepton.

The difficulty in finding these events lies in identifying all four leptons in the detector. Some leptons might fall outside the instrumented region of the detector while others may fail to meet the criteria used to select a lepton for the analysis. With four chances to miss a lepton, even small inefficiencies will add up. In a new analysis at DZero, analyzers make a focused effort to improve lepton selection and boost the efficiency for finding events with two Z bosons.

The new analysis finds a total of 13 candidate events in the full Tevatron Run II data set, collected over the course of a decade. This handful of observed events is consistent with the Standard Model expectation for simultaneous Z boson pair production. Since the Higgs boson can also decay into pairs of Z bosons, the analyzers also extended their analysis to search for hints of the Higgs boson. No significant excess of events was observed in the search, as expected considering the sensitivity of this analysis to Higgs boson production. Measurements of rare processes are important probes of the Standard Model, which passes this test with all aces.

Mike Cooke

These analyzers made significant contributions to this analysis.
The DZero algorithms and computing coordinators organize the collaboration’s efforts to develop and maintain the core software packages and computing infrastructure used to perform physics analyses.