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 Select Z + 2 jet events  Make VBF like cuts

Fitting for a Z VBF signal Christian Gutschow , Kiran Joshi, Emily Nurse, Andy Pilkington SM EWK meeting, 10 th August 2012.  Select Z + 2 jet events  Make VBF like cuts  Fit to one discriminating variable for the number of signal and background events.

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 Select Z + 2 jet events  Make VBF like cuts

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  1. Fitting for a Z VBF signalChristian Gutschow, Kiran Joshi, Emily Nurse, Andy PilkingtonSM EWK meeting, 10th August 2012  Select Z + 2 jet events  Make VBF like cuts  Fit to one discriminating variable for the number of signal and background events

  2. Datasets and cuts • 5.6 fb-1 of 8 TeVZμμ and Zee candidates • Background: Sherpa QCD Z + jets samples • Blah • Blah • Signal: Currently using 7 TeV Sherpa EWK samples • Z candidate • Two jets, pT1 > 45 GeV, pT2 > 35 GeV • Jet veto: No jets in between the two leading jets with pT > 25 GeV • ΔΦ(j,j) > π/2 • ΔΦ(Z,jj) > 2.9 • Fit the mjj distribution

  3. Fits to 8 TeV electron + muon Use signal template from 7 TeV Background Background+Signal Signal events: Input = 71 events (assuming 30% larger cross-section at 8 TeV) Fit for 79 +59 -55 We should have 3 times this dataset for HCP More events for W production

  4. 1000 MC toys with 3 times the data (16.8 fb-1) 213 input events ~2σ significance

  5. mjj background shape • Can we define control regions to test the Sherpa model of the background shape? • Z candidate Keep these cuts • Two jets, pT1 > 45 GeV, pT2 > 35 GeV • Jet veto: No jets in between the two leading jets Remove, relax or reverse • ΔΦ(j,j) > π/2 • ΔΦ(Z,jj) > 2.9 signal region

  6. mjj in control regions Remove all, reverse Φ(Z,jj) Remove all cuts In events where the Z and di-jet system do not balance: MC overestimates mjjtails • These events generally either: • have additional jets, or • the di-jet system comes from DPI or pileup

  7. Look at events with Φ(Z,jj) < 2.5 and mjj > 750 GeV

  8. mjj in control regions Remove all, reverse Φ(Z,jj) Remove all cuts No Z pT cut Z pT > 20 GeV

  9. mjj in control regions, with Z pT > 20 GeV Remove jet veto, relax Φ(Z,jj) > 2.7, reverse Φ(j,j) Signal region Remove Φ(j,j), relax Φ(Z,jj) > 2.7, require extra jet Relax Φ(Z,jj) > 2.7, require extra jet OR reverse Φ(j,j)

  10. Conclusion on control regions • Within the current limited stats the control regions are well described • We will have three (six) times the data and much more MC • We could use the W+jets events to check mjj in control regions

  11. JES systematic • Within the current limited stats the JES systematic is small • We will have much more MC • We could use the W+jets events to check the JES effect on mjj Make mjj background templates with JES scaled up one sigma Fit to a pol1

  12. JER systematic • Within the current limited stats the JER systematic is small • We will have much more MC • We could use the W+jets events to check the JER effect on mjj Make mjj background templates with JER scaled up one sigma Fit to a pol1

  13. How systematics effect mjj fits 1 – (0.1/3000)×mjj 1 – (0.2/3000)×mjj 1 – (0.3/3000)×mjj • So far not much sign of systematic shift within stats • Try weighting background mjj spectrum by a 1st order polynomial • Do 1000 toy MC fits to shifted template 213 input events 213 input events 213 input events ± ~60 events ± ~90 events ± ~140 events Recall statistical uncertainty ~100 events ~2σ significance

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