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Study of WZ production at DØ. Keti Kaadze Kansas State University For DØ collaboration. Motivation. Measure cross section, triple gauge couplings Explore physics beyond the SM The sequential heavy gauge bosons Search for Technicolor resonances - PowerPoint PPT Presentation
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Study of WZ production at DØ
Keti KaadzeKansas State University
For DØ collaboration
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 1
MotivationMeasure cross section,
triple gauge couplings
Explore physics beyond the SMThe sequential heavy gauge bosonsSearch for Technicolor resonancesED based Higgsless model, little higgs modelBackground to Higgs searches
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 2
Particles we searched for…
Sequential heave W-like boson, so-called W'
Within low scale TCLight techni-particles have masses < 500 GeVMostly decay with at least one gauge boson
±T/a±
T→W±T; ±T/a±
T→W±Z; T/T→T;
Very distinct signature, narrow resonances
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 3
WW
WWW M
MM '
'' 34)(
D0 detector
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 4
4.1 fb-1 is used in this search
Tracking2T solenoidCalorimetersMuon system
Event selectionFour signatures:
e/ + neutrinoWell identified, isolated,
high energetic leptons − pT >20 GeVInvariant mass constraint on Z boson candidate
80 < Mee < 102 GeV and 70 < M < 110 GeV
R(lZ,lW) = √(2+2) > 1.2Missing transverse energy > 30 GeV
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 5
pW
Z
pl
l
l
BackgroundsProcesses with at least three genuine leptons
WZ and ZZ production − estimated from MC simulation
Instrumental backgrounds due to wrongly identification of a jet, photon from processesZ+jets, Z − estimated using data-driven methodsttbar − estimated from MC simulation and found to
be negligible
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 6
Z+jetsGenuine Z candidate and misidentified jetMeasure the misidentification ratio
in multijet events from data
For each signature Z+”false” lepton sample is selected from datapT spectrum of “false” lepton is folded by fr
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 7
l
jet
l
€
fr =dN dpT (" true")dN dpT (" false")
ZBackground for WZlle
Due to track mismatch or photonconversion
Measure photon to electron misidentification rate in data feUse Z() final state radiation
Photon pT distribution is multiplied by pT dependent e misidentification rate
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 8
FSR
€
NZγ = σ llγ × Ldata × Accep × ε selection × fγ → e
Event yields
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 9
Very good agreement with the SM background prediction
Limits on W'→WZWe exclude sequential W'
188 GeV < M(W') < 520 GeV (obs.)188 GeV < M(W') < 497 GeV (exp.)
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 10
W'WZ coupling
)()()( '2
2'
WMWMSMWWZWZW
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 11
• Variation of coupling affects on (W') and Br(W'→WZ)
W'WZ Obs. (GeV)
Exp. (GeV)
1 (SSM) 520 4974 767 7529 903 88116 988 967
W' width studiesSSM W' is predicted to be a narrow resonance
Stronger W'WZ coupling results in increasing the width of the resonance
We studied and find limits stay within 1s.d. band for for W' resonances with width up to 25% of the mass
WW
WWW M
MM '
'' 34)(
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 12
Width of 500 GeV signal for different coupling strength ()
= 1 (SSM) 2 4 10 20 30Width (GeV)
17 18 22 45 130 271
TechnicolorPrevious searches were done in T/aT→WT→lbq
Allowed only if M(T) < M(T) - M(W)
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 13
Previously excluded region is M(T) < 220 GeV (DØ)
Limits on T→W
We exclude 208 GeV < M(T) < 400 GeV at 95% C.L. (obs.)201 GeV < M(T) < 339 GeV at 95% C.L. (exp.)
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 14
M(T) > M(T) - M(W)
decay to WZ is dominant
ConclusionThe first search for a new resonance in WZ
production is performed at the DØ experimentSSM W' with masses 188-520 GeV is excludedSet limits on W'WZ couplings predicted in
different extensions of the SMExcluded typical TC phase space for heavy
techni-pions
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 15
arXiv:0912.0715v3 [hep-ex]
Published at PRLhttp://prl.aps.org/abstract/PRL/v104/i6/e061801
BACKUP
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 16
W’ Signal cross section & BrSSM(W’->WZ)
February 16, 2010Lake Louise Winter Institute, Keti Kaadze 17