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VBF at CDF

VBF at CDF. Laura Gilbert, Sinead Farrington, Chris Hays Oxford 13 th August 2008. Madgraph σ = 3.3 fb VBFNLO σ = 7.7 fb. Madgraph σ = 8.8 fb VBFNLO σ = 38 fb. Cross sections: Madgraph/VBFNLO. We don’t understand why these differences are so large Using cuts: pt(lepton)>15GeV

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VBF at CDF

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  1. VBF at CDF Laura Gilbert, Sinead Farrington, Chris Hays Oxford 13th August 2008

  2. Madgraph σ = 3.3 fb VBFNLO σ = 7.7 fb Madgraph σ = 8.8 fb VBFNLO σ = 38 fb Cross sections: Madgraph/VBFNLO • We don’t understand why these differences are so large • Using cuts: pt(lepton)>15GeV • Could be remaining cuts hidden in madgraph that we couldn’t find… • Depends on many input parameters

  3. Analysis Plan • Use Sherpa to simulate the VBF events • Generated samples with and without WWZ vertex switched on • Ultimate observation (or limit) would relyon comparing data with the sample • with and without VBF processes included • Optimise selection to maximise VBF observation potential • Technical hitches with converting hepevt output into HEPG format to run through • CdfSim – work in progress • Have generated W, Z decaying to muons and electrons in Sherpa – will cover all modes • In the mean time we have validated sherpa on an existing Sherpa Z to mm sample • Surprisingly good comparison (see Laura’s slides) • Why Sherpa? – processes not included in pythia/herwig • VBFNLO cannot generate NLO “events”, so no NLO benefit • VBFNLO doesn’t include the full event as sherpa does

  4. Open Questions • How do we define control regions and keep ourselves “blinded” while optimising • Infrastructure – we are using Duke ntuples

  5. Plots • Blue: sherpa simulation Z->mumu+2+jets • Black: run II data • Two jets pT > 15 GeV required

  6. Muon plots • Muons good for Z selection • Two “tight” muons in fiducial regions • Opposite charge • Delta t0 < 4 ns • Delta z0 < 5 cm

  7. Z plots • Z variables reconstructed • MET reconstructed

  8. Jet plots • Assuming sample contains at least 2 jets pT > 15 GeV • Plotting jets pT > 20 GeV

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