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Mark Neubauer University of Illinois at Urbana-Champaign ( for the ATLAS Collaboration )

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 {.

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Mark Neubauer University of Illinois at Urbana-Champaign ( for the ATLAS Collaboration )

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  1. Search for Diboson Production in the Lepton + MET + Jets Final State DPF 2011 Meeting Brown University August, 10th2011 Mark Neubauer University of Illinois atUrbana-Champaign (forthe ATLAS Collaboration)

  2. Dibosons @ Hadron Colliders σ(pb) O(1-10) pb{ • 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 DPF 2011 @ Brown University / Aug 10, 2011

  3. Dibosons in Higgs Search This talk focuses on lepton + MET + 2 or 3 jets • Dibosons play a central role in Higgs searches for mH > 135 GeV • WW is the dominant decay channel • ZZ channels very clean DPF 2011 @ Brown University / Aug 10, 2011

  4. Higgs Boson Production @ LHC Signal ratesandtheoreticaluncertainties (mf, mr, PDF andαs)fromarXiv:1101.0593 [hep-ph] DPF 2011 @ Brown University / Aug 10, 2011

  5. LHC Delivers, ATLAS Collects 2011 to-date: ε≈95% 1.04 pb-1used for results in this talk • 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) DPF 2011 @ Brown University / Aug 10, 2011

  6. ATLAS Diboson Measurements Single boson and diboson cross section measurements in the leptonic decay channels DPF 2011 @ Brown University / Aug 9, 2011

  7. Lepton + MET + Jets Motivation • WWdominant Higgs decay channel for MH>135 GeV • lvlv dominates our Higgs sensitivity for 135 < MH< 200 GeV • lvqqdominates WW sensitivity for 240 < MH< 600 GeVdue to: • Larger W branching fraction • Dominant 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

  8. Analysis Overview • Select events with one high-pTe/μ, 2 or 3 jets, and large MET • M(lvjj) to discriminate signal and background: M(lv) = M(W) • Objection selection • Lepton: pT> 30 GeV, |η| < 2.5 • Jet: ET> 25 GeV, |η| < 4.5 • “Neutrino”: MET > 30 GeV • Event selection / categorization • 71 < M(jj) < 91 GeV • Require real pν,zsolution • Separate categorization for H+0j and H+1j • Data-driven background • Signal modeled by POWHEG + PYTHIA DPF 2011 @ Brown University / Aug 9, 2011

  9. Data-Driven QCD Estimates μ± e± H + 0 j μ± e± H + 1 j DPF 2011 @ Brown University / Aug 9, 2011

  10. Yields after MET Fits • Expected and observed yields after MET fit • Real M(lvjj) solution requirement not applied Good agreement with expectations DPF 2011 @ Brown University / Aug 9, 2011

  11. Some Kinematic Distributions H + 0 j H + 1 j DPF 2011 @ Brown University / Aug 9, 2011

  12. Dijet Invariant Mass Signal selection: [71, 91] GeV Sideband selections: [50, 60]GeV (low sideband) and [100,110] (high sideband) DPF 2011 @ Brown University / Aug 9, 2011

  13. Background Model High mass sideband Low mass sideband Double-exponential model, well-motivated by MC and validated in M(jj) sidebands of the W boson DPF 2011 @ Brown University / Aug 9, 2011

  14. M(lvjj) Distributions No evidence for a resonance in the M(lvjj) spectrum DPF 2011 @ Brown University / Aug 9, 2011

  15. Cross Section Limits 95% C.L. limits @ 400 GeV: σ < 3.1 pb (2.7 × SM) DPF 2011 @ Brown University / Aug 9, 2011

  16. M(lvjj) Distribution DPF 2011 @ Brown University / Aug 9, 2011

  17. Background-Subtracted M(lvjj) DPF 2011 @ Brown University / Aug 9, 2011

  18. Summary • 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! DPF 2011 @ Brown University / Aug 9, 2011

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