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Search for Diboson Production in the Lepton + MET + Jets Final State. DPF 2011 Meeting Brown University August, 10 th 2011. Mark Neubauer University of Illinois at Urbana-Champaign ( for the ATLAS Collaboration ). Dibosons @ Hadron Colliders. σ ( pb ). O(1-10) pb {. - PowerPoint PPT Presentation
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Mark NeubauerUniversity of Illinois at Urbana-Champaign(for the ATLAS Collaboration)
DPF 2011 MeetingBrown University
August, 10th 2011
Search for Diboson Production in the Lepton + MET + Jets Final
State
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• Diboson production: gauge boson self couplings Couplings intimately related to gauge structure
of the SM and electroweak symmetry breaking Sensitive probe of new phenomena
Higgs, SUSY, LED, technicolor, Higgsless, … Important background to many searches
Higgs, SUSY, LED, technicolor, Higgsless, … Demonstrate sensitivity to small cross section
processes in the SM
Dibosons @ Hadron Colliders
Mark Neubauer DPF 2011 @ Brown University / Aug 10, 2011
σ(pb)
O(1-10) pb {
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• Dibosons play a central role in Higgs searches for mH > 135 GeV
WW is the dominant decay channel
ZZ channels very clean
Dibosons in Higgs Search
Mark Neubauer DPF 2011 @ Brown University / Aug 10, 2011
This talk focuses on lepton + MET + 2 or 3 jets
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• Signal rates and theoretical uncertainties (mf, mr, PDF and αs)from arXiv:1101.0593 [hep-ph]
Higgs Boson Production @ LHC
Mark Neubauer DPF 2011 @ Brown University / Aug 10, 2011
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• Data collected in 2011 (pp collisions at √s = 7 TeV) Peak luminosity Linst = 2.11 × 1033 cm-2 s-1
Mean number of interactions per bunch crossing μ=5.7 ΔL / L = ± 3.7% (2011, preliminary)
LHC Delivers, ATLAS Collects
Mark Neubauer DPF 2011 @ Brown University / Aug 10, 2011
2011 to-date: ε≈ 95%
1.04 pb-1 used for results in this talk
DPF 2011 @ Brown University / Aug 9, 2011
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• Single boson and diboson cross section measurements in the leptonic decay channels
ATLAS Diboson Measurements
Mark Neubauer
DPF 2011 @ Brown University / Aug 9, 2011
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Lepton + MET + Jets Motivation
Mark Neubauer
• WW dominant Higgs decay channel for MH>135 GeV lvlv dominates our Higgs sensitivity
for 135 < MH< 200 GeV lvqq dominates WW sensitivity for 240 < MH< 600 GeV due to:
Larger W branching fractionDominant background (W+jets) falls
off rapidly with increasing M(lvjj)Full Higgs mass reconstruction
lvqq complements ZZ channels with comparable sensitivity
Weak Boson Fusion (WBF) in lvqq channel a stepping stone to Weak Boson Scattering (WBS) for deep study of EWSB
DPF 2011 @ Brown University / Aug 9, 2011
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• Select events with one high-pT e/μ, 2 or 3 jets, and large MET
• M(lvjj) to discriminate signal and background: M(lv) = M(W)
Objection selectionLepton: pT > 30 GeV, |η| < 2.5Jet: ET > 25 GeV, |η| < 4.5“Neutrino”: MET > 30 GeV
Event selection / categorization71 < M(jj) < 91 GeVRequire real pν,z solutionSeparate categorization for H+0j and H+1j
Data-driven background Signal modeled by POWHEG + PYTHIA
Analysis Overview
Mark Neubauer
DPF 2011 @ Brown University / Aug 9, 2011
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Data-Driven QCD Estimates
Mark Neubauer
H + 1 j
H + 0 j
e±
e±
μ±
μ±
DPF 2011 @ Brown University / Aug 9, 2011
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• Good agreement with expectations
Yields after MET Fits
Mark Neubauer
Process Events in 1.04 fb-1
W/Z + jets 38080 ± 1170
QCD Multi-jets 2027 ± 43
Top 1330 ± 270
Dibosons 1180 ± 240
Total Expected Background 42600 ± 1200
Observed 41687
Expected Signal (mH=400 GeV)
58 ± 15
• Expected and observed yields after MET fit Real M(lvjj) solution requirement not applied
DPF 2011 @ Brown University / Aug 9, 2011
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Some Kinematic Distributions
Mark Neubauer
H + 1 j
H + 0 j
DPF 2011 @ Brown University / Aug 9, 2011
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Dijet Invariant Mass
Mark Neubauer
Signal selection: [71, 91] GeVSideband selections: [50, 60] GeV (low sideband) and [100,110] (high sideband)
DPF 2011 @ Brown University / Aug 9, 2011
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• Double-exponential model, well-motivated by MC and validated in M(jj) sidebands of the W boson
Background Model
Mark Neubauer
High masssideband
Low masssideband
DPF 2011 @ Brown University / Aug 9, 2011
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• No evidence for a resonance in the M(lvjj) spectrum
M(lvjj) Distributions
Mark Neubauer
DPF 2011 @ Brown University / Aug 9, 2011
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Cross Section Limits
Mark Neubauer
95% C.L. limits @ 400 GeV:
σ < 3.1 pb (2.7 × SM)
DPF 2011 @ Brown University / Aug 9, 2011
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M(lvjj) Distribution
Mark Neubauer
DPF 2011 @ Brown University / Aug 9, 2011
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Background-Subtracted M(lvjj)
Mark Neubauer
DPF 2011 @ Brown University / Aug 9, 2011
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• Diboson production provides a sensitive probe of the Higgs and new physics
• Channels involving a W->qq’ decay play an important role in the searches, especially at large diboson invariant mass
• We searched for Higgs production in the lepton + MET + 2 or 3 jet final state and place limits on the production
• Many improvements anticipated Better pileup suppression Weak boson fusion Charm tagging Multivariate techniques More data!
Summary
Mark Neubauer