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Introduction
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Analysis Methods
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Summary of Results
Introduction
We report a measurement of Z0Z0 production
in the ppbar collisions at √s=1.96 TeV using the combination
of the four charged (e,μ) lepton and the two charge lepton
two neutrino final states. At tree
level, only the t-channel process, shown in the left diagram below,
contributes to Z0Z0 production. If an
anomalous (not in the Standard Model) triple gauge coupling
(ZZ&gamma and ZZZ)
exists, then an additional contribution would be made by the
s-channel diagram (below right).
t-channel
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s-channel
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Lepton Selection
A summary of the lepton selection categories and acceptances are shown
in the figures below. For more details see
WZ Observation PRL
Electron Identification Categories
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Muon Identification Categories
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Summary of Results
Candidates with 4 leptons are selected which have to Z candidates: one with 76 < mll < 106 GeV
and one with 40 < mll < 140 GeV. The dominant backgrounds are Z+jets and Zγ+jets
where two jets or a γ and a jet are misidentified as leptons. Because the trackless forward
electons have much larger backgrounds we divide the sample into two channels: candidates that involve
trackless electrion and those that do not. The background predictions and yields are found below.
The background prediction methods are described in the
PRL .
ZZ decaying to 4 charged leptons
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TEX or GIF of
Signal and background expectations and observed events in
the signal region for the Z0Z0 to four charge lepton
search analysis.
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Plots for ZZ decaying to 4 charged leptons
Candidates with 2 charge-leptons and large Missing Transverse Energy (MET).
This sample has significant backgrounds from WW, WZ, W+jets, Wγ, ttbar and Drell-Yan
The detailed selection and background prediction methods are described in the
PRL .
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TEX or GIF of
Signal and background expectations and observed events in
the ZZ to llνν fit region.
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TEX or GIF of
Systematic uncertainties on the expected llνν fit region.yield in percent.
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Likelihood Ratio plots for llνν fit
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JPG or
EPS
Likelihood Ratio Distribution
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JPG or
EPS
log (1-Likelihood Ratio Distribution)
(distribution actually fit)
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TEX or EPS or GIF of
Probability of the observing a Z0Z0 with 2, 3, and 5 σ
significance
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The observed signal has a P-value of ± which corresponds to a
4.4 σ one-side Gaussian significance. We find the cross-section to be:
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This is to be compared the on-shell Z0Z0
cross-section 1.4 ± 0.1 pb at NLO.
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We use 4 control regions to validate the data modeling. Each
is particularly sensitive to a different set of uncertainties.
They are:
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The Drell-Yan Control Region is the same lepton
selection, but with a MET < 25 GeV requirement instead of the MET special and MET
signficance cuts and tests the lepton identification, trigger efficiency,
and luminosity/cross-section calculations.
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The Same-Sign Control Region is the
same event selection, but with an same sign instead of opposite sign
requirement on the lepton charges. This region tests
the modeling of jets and photons misidentified as leptons.
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The Low Met Significance Control Region is the
same event selection, but with the MET significance required to be less instead of
greater than 2.5 GeV1/2. This tests the modeling of false MET due
the uncluster energy resolution.
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The Low Met Special Control Region is
the same event selection, but with the Met Special required to be between
15 and 25 GeV instead of above 25 GeV. This tests the effects of lost lepton
or jet energy.
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The two met control regions are shown graphically here:
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EPS or GIF
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TEX or GIF of
Expected and observed events in the Drell-Yan Control Region
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TEX or GIF of
Expected and observed events in the Same-Sign Control Region
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TEX or GIF of
Expected and observed events in the Low Met Significance Control Region
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TEX or GIF of
Expected and observed events in the Low Met Special Control Region
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