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W' Search in the single top quark channel

W' Search in the single top quark channel. Reinhard Schwienhorst Michigan State University. Top Group Meeting, 2/24/2005. Outline. Single top status W' introduction Analysis procedure Outlook/Conclusions. Single top status. Neural Network analysis with 230 pb -1 published

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W' Search in the single top quark channel

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  1. W' Searchin the single top quark channel Reinhard Schwienhorst Michigan State University Top Group Meeting, 2/24/2005

  2. Outline Single top status W' introduction Analysis procedure Outlook/Conclusions

  3. Single top status Neural Network analysis with 230 pb-1 published Likelihood-based analysis with 360 pb-1 at conferences t-channel s-channel u q t d W W b t b q' NLO calculation: 0.88pb (±8%) 1.98pb (±11%) 95% CL limits, NN: < 6.4 pb < 5.0 pblikelihood: < 5.0 pb < 4.4 pb

  4. Introduction Many extensions of the SM involve heavy gauge bosons Typically called W' and Z' From larger, extra gauge symmetry groups Could interact differently with leptons and quarks Current limits: M(W'anything) > 786 GeV W' q q'

  5. W' in the single top quark channel Single top quark production is the ideal place to search for hadronic decays of a W' W' searches in the light quark decay channels are swamped by multijet background Current limits: M(W'qq') > 800 GeV W' model used here: W'tb with SM-like couplings Include interference with SM W boson in event generation b W' q t l W n q' b

  6. W' Signal final state invariant mass

  7. Analysis procedure Follow procedure used in DØ single top publication 230 pb-1 dataset Stradivarius top_analyze samples Same background estimation methods, scale factors, efficiencies, smearing, ... Apply s-channel single top selection cuts Lepton pT>15GeV, MET>15GeV, jet pT>15GeV Tighter jet selection: 2  njets 3 Remove top pair background Then form binned likelihood using invariant mass distribution No NN, DT, LH, ...

  8. Analysis Strategy full dataset muon electron =2 b-tags =2 b-tags =1 b-tag =1 b-tag Ŝ distribution binned likelihood W'(800GeV) W'(600GeV) W'(700GeV) result W'(800GeV) W'(600GeV) W'(700GeV)

  9. Final state invariant mass

  10. Data-Background comparison

  11. Limit Setting Procedure Use Ŝ distribution to set limits In window 400GeV  Ŝ 1000GeV Including all systematic uncertainties b-tag modeling 4 – 16% 5 – 20% Jet energy calibration 1 – 2% 15 – 30% Others (trigger, ID, ...) 1 – 5% 1 – 5% Set limits separately for 600 GeV, 700 GeV, 800GeV signal backgrounds s600 GeV < 1.8 pb < 1.7 pb s700 GeV < 1.6 pb < 1.4 pb s800 GeV < 2.1 pb < 2.1 pb Expected limit: Measured limit:

  12. Result

  13. Conclusions/Outlook First search for W' boson production in top quark decay channel No evidence for a W' boson in 230pb-1 of data Mass limit: M(W') > 650 GeV For a W' boson with SM-like coupling to SM fermions

  14. Additional Material

  15. Event Selection • Trigger: • Electron + 1 jets, muon + 1 jets • Lepton: • 1 electron: pT > 15GeV, |hdet|<1.1 • 1 muon: pT > 15GeV, |hdet|<2.0 • Neutrino: ET > 15GeV • Jets: • pT > 15GeV, |hdet|<3.4, • 2  njets 3 •  1 b-tagged jet • Reject mis-reconstructed events lepton neutrino b-quark b-quark pT (jet 1)> 25GeV |hdet(jet1)|<2.5

  16. Background Modeling Based on data as much as possible W/Z+jets production Estimated from MC/data Distributions from MC Normalization from pre-tagged sample Flavor fractions from NLO Multijet events (misidentified lepton) Estimated from data Top pair production Estimated from MC Diboson (WZ, WW) Estimated from MC l W q n q (b) g q' q (b) l n q t b b t q' g q q

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