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WW/WZ production in electron-neutrino plus dijet final state at CDF APS April Meeting

WW/WZ production in electron-neutrino plus dijet final state at CDF APS April Meeting 14-17 April 2007 Jacksonville, FL Anna Sfyrla (CDF Collaboration) University of Geneva, Switzerland. WW/WZ Production.

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WW/WZ production in electron-neutrino plus dijet final state at CDF APS April Meeting

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  1. WW/WZ production in electron-neutrino plus dijet final state at CDF APS April Meeting 14-17 April 2007 Jacksonville, FL Anna Sfyrla (CDF Collaboration) University of Geneva, Switzerland

  2. WW/WZ Production • WW/WZ observed so far only in the fully leptonic decay channel, in hadron colliders • Aim of this analysis the observation in the semi-leptonic channel! • X-Section Measurement • comparison with SM theoretical predictions • Triple gauge couplings (WWZ/γ) • favorable channel for the triple gauge couplings due to the big branching ratio with respect to the leptonic channel • Significant background for other interesting processes • ex. H  WW • Channel topologically similar to WH  lνbb • techniques developed in this analysis are also applicable there WZ Production WW Production 2

  3. The CDF Detector A general purpose detector at TeV, FNAL Designed with the classic layered structure Central EM Calorimeter Central Hadronic Calorimeter Central Inner Tracker (Silicon) Main objects in this analysis Electrons Reconstructed in the Central EM Calorimeter using tracking information Neutrinos Missing transverse energy Jets Reconstructed in the calorimeter Muon Chambers Forward Calorimeter Central Outer Tracker (Drift Chambers) 3

  4. Event Selection & Backgrounds Signal Definition Exactly 1 Central Electron Missing Transverse Energy > 25 GeV 2 or more Jets (PT>15GeV) Similar Event Topology (Backgrounds) W  eν + jets W  τν+ jets Z  ee + jets QCD t-tbar e ν jet W jet W/Z σWW*BR= 12.4 pb *0.146 = 1.81 pb σWZ *BR= 3.96 pb *0.07 = 0.28 pb σW(e)jj = 320.4 pb Signal/Background initially very poor 4

  5. Analysis methodology – 1. INITIALLY Very Poor S/B Maximum Significance Gain [Significance = S/(S+B)] Dijet Inv. Mass VAR 1 VAR 3 Neural Network VAR 5 VAR 2 VAR 4 0 NN OUT 1 VAR 6 AFTER NN CUT Dijet Inv. Mass 5

  6. Analysis methodology – 2. Overall parameterization fs*ψ(x) + (1-fs)*φ(x) Dijet Inv. Mass Dijet Inv. Mass Dijet Inv. Mass Signal shape fixed using MC Background parameterization motivated by MC Both plugged into a likelihood fitter Background parameters and signal fraction given by likelihood fit to data CLs method A L Read 2002 J. Phys. G: Nucl. Part. Phys.28 2693-2704 used to give the sensitivity of the analysis and the significance of the measurement S+B Hypothesis B-Only Hypothesis -2logQ 6

  7. Dijet invariant mass before NN training Signal Region Overall S/(S+B)=3. Signal region S/(S+B)=3.5 (MC) Signal Region 7

  8. NN training Signal BGR JETNET NN NN Input angles or angle-related variables NN Output as less correlated to the dijet invariant mass as possible Point of Maximum Significance Gain 8

  9. Dijet invariant mass after NN training Overall S/(S+B)=3.4 Signal region S/(S+B)=4.2 Expected significance ~4σ Gain of ~20% in significance!! Signal Region 9

  10. Likelihood fit to data P-value: ~0.0065 2.7σ significance 10

  11. Measured Numbers Systematics Summary Having used 1.29 fb-1 of data Measured Number of WW/WZ Events (mjj[40,160]GeV) 266 ± 173 (stat) ± 40 (sys) Cross section (mjj[40,160]GeV) σBR = (1.45 ± 0.95 (stat) ± 0.29 (sys)) pb Theoretical σBR = 2.1 ± 0.2 pb [BR : (Weν,W/Zjj) ] 95%CL upper limit σBR(Weν,W/Zjj) < 3.4 pb 11

  12. Summary A search for WW/WZ in the semi-leptonic decay channel has been presented, using 1.29 fb-1 of the CDF data So far in the analysis Central electrons have been used in the lepton selection & the event selection is optimized with the use of a Neural Network A 2.7σ significance measurement has been performed The measurement is statistically limited at this stage Next Steps in the analysis There is a lot of potential for improvement! Adding muons and forward electrons in the event selection and adding more data, the event yield can be more than doubled, introducing a large factor in the significance! Search for Anomalous Gauge Couplings will follow 12

  13. Backup

  14. DATA-MC agreement - NN output Point of Maximum Significance Gain 14

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