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W' Search in the single top quark channel

Explore the status of the elusive W' particle in the single top quark channel. Analysis with neural networks and likelihood-based methods presents limits and calculations. Investigate heavy gauge bosons beyond the Standard Model through top quark production. Detailed procedure and outcomes for W' decays to different quarks and leptons. Strategy for setting mass limits and comparing data with background. Anticipated and observed limits for various signal backgrounds and systematic uncertainties. Conclusions and future outlook of the first search for W' boson production in top quark decays. Additional event selection criteria and background modeling using various methods.

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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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