Measurement of Diboson Production at the Tevatron Ivor Fleck Universität Freiburg for the CDF and DØ collaborations Diboson production - WW - WZ/ZZ - W- Zanomalous couplings - all measurements in RunII, i.e. √s = 1.96 TeV - (nearly) all measurements use only leptonic final states of W and Z bosons
Measurement of Diboson Production at the Tevatron. Ivor Fleck Universität Freiburg for the CDF and D Ø collaborations. Diboson production - WW - WZ/ZZ - W g - Z g anomalous couplings. - all measurements in RunII, i.e. √s = 1.96 TeV - PowerPoint PPT Presentation
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Measurement of Diboson Production at
the TevatronIvor Fleck
Universität Freiburg
for the CDF and DØ collaborations
Diboson production- WW- WZ/ZZ- W- Z
anomalous couplings
- all measurements in RunII, i.e. √s = 1.96 TeV- (nearly) all measurements use only leptonic final states of W and Z bosons
Diboson Productiontest of non-ablelian component
of SM SU(2)L x U(1)Y
sensitive for anomalous couplingsbackground for searches, especially Higgs understanding important
t-channel
)cot( we couplings: WW, WWZ, forbidden: ZZ, Z
u-channel
s-channel
t-channel: cross section violatesunitarity for s ∞
(for massless quarks and large s)s-channel cancels unitarity violation in t- and u-channelfor WW, WZ and W production
3)(
2 sGWW F
)cot( we e
WW Coupling WWZ Coupling
W
WW
W
Z
WW and WWZ anomalous couplings
SM: 5 CP conserving parameters:
( g
gg
in W production, only WW couplings
in WZ production, only WWZ couplings
in WW production, both couplings
nss
)/ˆ1()ˆ(
2
n 2 for WW ,WWZ
PT(W) (GeV/c)
# E
vent
s/20
GeV
/c
/\ : form factor to avoid unitarity violation at large s
anomalous couplings lead to excess of events
for large ET of gauge bosons
VWW VWW
)WVWVWW(/L
†2
V†V
††1VWWVWWV
WM
gg
V = Z or
W
W
Z/
WW Productiontwo triple gauge couplings present: WWZ and WW (same final state also in Higgs production)observed final states: dilepton events (ee, e,) + missing ET
event selection:- two leptons (e or ) with pT > 20 (15) GeV
two analyses: dilepton and lepton plus track, i.e. second lepton identified by track anddoes not have to meet lepton ID criteria dilepton has better sensitivityobserve 17 events with 5.0 background events
pb (lum)9.0)syst()stat(8.13 2.19.0
3.48.3
pb (lum)9.0)syst()stat(6,14 8.10.3
8.51.5
PhysRevLett 94, 041803
PhysRevLett 94, 151801
WW in jets plus lepton final states
first analysis with W/Z decaying in jets
final state from Wℓ and W/Zqq
advantage: much larger branching ratiodisadvantage: much lager backgrounds
main background: W + 2jets productionfit background in sideband
fit in signal region yields:
observed 66 78 34 eventswith 91 events signal expectation < 40 pb at 95% CL
anomalous couplings limits from WW
most sensitive variable for anomalous couplings: pT of W
formed using lepton and ET,miss ()
anomalous couplings most visible at largepT of W
figure shows signal with anomalous couplings = = 0.5
limits at 95% CL:
-0.42 < < 0.58-0.32 < < 0.35
WZ Production
NLO cross section: 3.7 ± 0.1 pb
trilepton final states: eee, ee,e,very low background, very low BR~1,5%
lepton pair mass consistent with Z massobserve: 3 events with 0.71 ± 0.08 background eventsand 2.04 signal expectation main backgrounds:- Z+jets: 0.35±0.02, Z+: 0.15±0.02, ZZ: 0.20±0.07
< 13.3 pb at 95%CL probability of fluctuation 0.71 3 is 3.5 %, less than 3 hep-ex/0504019, submitted to PRL
pb )syststat(5,4 8,36,2
-only single triple gauge coupling WWZ-LEP did not measure this vertex independently of WW vertex-Final state not observed elsewhere
WZ Anomalous Couplings Limits
- inner limit from analysis at 95%CLfor = 1.5 TeV
- outer limit from S-matrix unitarity
= 1 TeV = 1.5 TeVg1
Z = Z = 0 -0.53<Z <0.56 -0.48<Z <0.48
Z = Z = 0 -0.57< g1Z <0.76 -0.49< g1
Z <0.66
Z = 0 -0.49< g1Z = Z < 0.66 -0.43< g1
Z = Z < 0.57
Z = g1Z = 0 -2.0< Z < 2.4 -
As no deviation from the SM expectation observed:set limit on anomalous couplings
WZ/ZZ ProductionCDF: search for ZW and ZZ combined with Lint = 194 pb-1
final states: ℓℓ , ℓℓ ℓℓ, ℓℓ ℓobserve 3 events withbackground expectation of 1.0 ± 0.2 events and signal expectation of 2.3 ± 0.3 eventslimit < 15.2 pb at 95%CL (PhysRev D71,091105)(SM: = 5.0 ± 0.4 pb, (ZZ) = 1.39 ± 0.10pb, (ZW) = 3.65 ± 0.26 pb)sensitive to neutral triple-gauge-couplings and WWZ couplings
W ProduktionFinal State RadiationInitial State Radiation
WW Vertex
main background source: W+jet events: 87.1 of 114 background eventsjet fake rate: 0.4% at 7 GeV, 0.1% at 18 GeV, 0.04% >40 GeV
jet fake rate
0.4% at 7 GeV
CDF: Lint = 200 pb-1, W e,
ET( > 7 GeV, |R(ℓ,) > 0,7
observe 323 events with 114 events background expectation
Theory (NLO): • BR (W ℓ) = 19,3 ± 1,4 pbσ • BR (W ℓ) = 18,1 ± 3,1 pbPhysRevLett 94, 211801
0.1% at 18 GeV
anomalous couplings limits from W
D0: limits for anomalous couplings:1D limits at 95% CL