CDF

Search for high-mass ZZ Resonances

CDF
We search for high-mass resonances decaying into Z boson pairs using data corresponding to 6 fb-1 collected by the CDF experiment in pp collisions at 1.96 TeV. Eight pp → ZZ → llll events are observed, of which four have invariant masses MZZ consistent with 327 GeV/c2, and also have unexpectedly high values of PT(ZZ). However, analysis of the pp → ZZ → ll+MET and pp → ZZ → lljj final states does not confirm a heavy resonance decaying into a pair of Z bosons. 95% CL upper limits are set on the production cross section times branching ratio sigma(pp → X → ZZ) at 0.26 pb and 0.28 pb for two signal models.

ArXiv entry 1111.3432

Public analysis note

Plots: ZZ → llll channel:


M(ZZ) for eight ZZ → l+l-l+l- candidates (PYTHIA normalised to standard model prediction of 5.8 events). (.pdf file)

Invariant masses of dilepton pairs in eight ZZ candidate events: (a) Mll(1) versus Mll(2), with selected mass region outlined; and (b) Mll for all Z boson candidates. (.pdf file)

PT(Z) for Z boson candidates in (a) low-mass four-lepton candidates and (b) high-mass events (PYTHIA prediction normalised to four events in each plot) (.pdf file)

PT(ZZ) for (a) low-mass four-lepton candidates and (b) high-mass events (PYTHIA prediction normalised to four events in each plot) (.pdf file)

(a) Number of jets and (inset) ET of leading jet; and (b) MET for four-epton candidate events. MET distribution for G*+jet process is normalized to 4 events. (.pdf file)


ZZ → ll + MET channel:


(a) Δ(φ)min for ee+MET and μμ+MET events as used for Z+jets normalization; and (b) Mll for same-sign dielectron pairs with large MET used to validate the W+jets background estimation. (.pdf file)

MET distribution for events with opposite-sign lepton pairs (ee+μμ). The contribution of Z_jets is normalized in the region 50 GeV < MET < 100 GeV using events with low |Δ(φ)min|. (.pdf file)

MvisZZ for (a) electron and (b) muon channels. The expected contribution from a graviton of M(G*)=325 GeV/c2 and cross section times branching ratio to ZZ of 1 pb is shown together with the expected contribution of boosted G*, produced in association with a jet. (.pdf file)


ZZ → ll + 2 jets channel:


Number of jets in (a) Z→ee+≥2jets and (b) Z→μμ+≥2jets events in the control region Mlljj<300 GeV/c2. (.pdf file)

M(lljj) for the (a) electron and (b) muon channels, showing the expected contribution from a G* of M(G*)=325 GeV/c2 and cross section times branching ratio to ZZ of 1 pb. (.pdf file)

M(lljj) for the (a) electron and (b) muon channels for PT(ZZ) > 40 GeV/c, showing the expected contribution from a boosted G* of M(G*)=325 GeV/c2 and cross section times branching ratio to ZZ of 1 pb. (.pdf file)

Limits:


Expected and observed 95% CL limits on sigma(pp → X → ZZ) from the Z → l+l-l+l- channel; the four events with MZZ=327 GeV/c2 result in a deviation from the expected limit. (.pdf file)

Expected and observed 95% CL limits on sigma(pp → X → ZZ) from the Z → ll + MET channel. (.pdf file)

Expected and observed 95% CL limits on sigma(pp → X → ZZ) from the Z → ll + 2 jets channel. (.pdf file)

Expected and observed 95% CL limits on sigma(pp → X → ZZ) from all channels combined. (.pdf file)


Supplemental approved material