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Studies of Diboson Production and Triple Gauge Coupling at LHC

Studies of Diboson Production and Triple Gauge Coupling at LHC. Zhengguo Zhao University of Michigan, Ann Arbor, USA On behalf of ATLAS and CMS ICHEP06, 7/26-8/2, Moscow, Russia. Outline. Introduction - Diboson production at LHC - Triple gauge boson couplings

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Studies of Diboson Production and Triple Gauge Coupling at LHC

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  1. Studies of Diboson Production and Triple Gauge Coupling at LHC Zhengguo Zhao University of Michigan, Ann Arbor, USA On behalf of ATLAS and CMS ICHEP06, 7/26-8/2, Moscow, Russia ICHEP06, Zhengguo Zhao

  2. Outline • Introduction - Diboson production at LHC - Triple gauge boson couplings • Studies with full simulation data - WZ, ZZ from CMS - WZ, WW and ZZ from ATLAS • Summary ICHEP06, Zhengguo Zhao

  3. V1 V3 V2 q V1 q V2 V1 q q’ q q’ V2 Diboson Production at Hadron Machine • LO Feynman diagram, V1, V2, V3 = Z, W, gWW, ZW, ZZ, Wg. • Only s channel has three boson vertex • Diboson final states have predictable productionandmanifest the gauge boson coupling SM: • Pure neutral vertexes ZZZ, ZZgare forbidden (Z/gcarry no charge and weak isospin that needed for gauge bosons couple) • Only charged couplings WWg, WWZ are allowed ICHEP06, Zhengguo Zhao

  4. l n  l W q W q’ l+ l- Z  l l’+ l’- l+ l- q q’ qbar Study of WZ, WW and ZZ at LHC • s-channel dominates, (SM) = 57.7 pb • Sensitive only to WWZ coupling • Clean signal eee, eem, mme, mmm • 3 isolated high pT leptons with large ET(miss) s-channel • (SM) = 127.5 pb • Sensitive to WWZ and WWg • Clean signal ee, mm,em • 2 isolated high pT leptons with opposite charge and large missing ET s-channel • s channel suppressed by O(10-4) • Only t-channel at tree level, (SM) = 16.8 pb • 4 isolated high pT leptons from the Z pair decays • Clean signal eeee, eemm, mmmm, almost bkg free t-channel ICHEP06, Zhengguo Zhao

  5. Triple Gauge Boson Couplings • Characterized by an effective Lagrangian, parameterized in terms of coupling parameters for new physics • C, P and CP symmetry conservation, 5 free parameters: - lg ,lZ: grow with s, big advantage for LHC -kg = kg-1, g1Z = g1Z-1, kZ = kZ-1:grow with√s • Tree level SM: lg =lZ =kg = g1Z = kZ = 0 ICHEP06, Zhengguo Zhao

  6. Anomalous Coupling and Form Factor • Cross section increase for coupling with non-SM values, yielding large cross section at high energies that violating tree level unitarity  form factor scale s: subprocess CM energy. L: formfactor scale • TGCs manifest in - cross section enhancement - high pT(V=Z,W,) - production angle ICHEP06, Zhengguo Zhao

  7. LHC Expectations for the TGCs LHC • High CM energy  larger s • High luminosity  high statistics • High sensitivity  Expected to be ~×10 improvement on LEP/Tevatron Predictions for TGCs at 95% C.L. for L=30 fb-1 (inc syst) ICHEP06, Zhengguo Zhao

  8. Motivations •Measure dibson production  and TGCs • Explore none-Abelian SU(2)U(1) gauge structure of SM and test the central part of the SM •Probe new physics if production cross section, or TGCs deviate from SM prediction  complementary to direct search for new physics • Understand the backgroundsof many important physics analyses Search for Higgs, SUSY, graviton and study of ttbar ICHEP06, Zhengguo Zhao

  9. H ZZ Diboson as Background ICHEP06, Zhengguo Zhao

  10. Signal Main bkg Signal and Background Samples (CMS) tt(2l) generated with TopReX, Zbb with CompHEP, all others with Pythia ICHEP06, Zhengguo Zhao

  11. Expected signal and background yields for 1 fb-1 WZ→3l Expected Signal & Background • M(l+l-) after all cuts 4 channels combined (3e,2e1m,2m1e,3m) • Presence of peaking backgrounds - Zbb - ZZ (irreducible) • High significance in the first 1 fb-1 L = 1 fb-1 ICHEP06, Zhengguo Zhao

  12. L = 10 fb-1 ZZ→4e Expected Signal & Background M(e+e-) after all cuts (2 entries per event) Nearly background free! Expected signal and background yields for 1 and 10 fb-1 ICHEP06, Zhengguo Zhao

  13. Ideal simulation Ideal simulation miscalibration miscalibration Systematic effects Systematic effects 0 WZ and ZZ Discovery Potential (CMS) ZZ→4e signal significance WZ →3l signal significance 5 s discovery at: • ZZ : ~1 fb-1 • WZ : ~150 pb-1 ICHEP06, Zhengguo Zhao

  14. MC Data for Diboson Studies(ATLAS) • Data produced in ATLAS GRID, and Michigan ATLAS computer cluster • Background (pythia 6.2), 106 ~ 107 for Z+jet, W+jet, DY, W+jet and Wlepton • Signal events produced by MC@NLO (v2.3)–Jimmy, W/Z width effect is not included (v3.1 has included width) ICHEP06, Zhengguo Zhao

  15. WZ WW WW MZ(ee) Vector∑Et(jet) to reject jet Vector∑Et(jet) cut tt cut MZ(mm)-MW(en) Pt(l+l-) cut to reject fate events Pt(l+l-) WW Zjet Zg ZZ ICHEP06, Zhengguo Zhao

  16. 2.1% 7.7% 47.4% 42.9% ZW Signal and Backgrounds (ATLAS) (for 1 fb-1 data) ICHEP06, Zhengguo Zhao

  17. 2.6% 3.4% 8.3% 47.3% 38.4% WW Signal and Background (ATLAS) (for 1 fb-1 data) ICHEP06, Zhengguo Zhao

  18. M(e+e-) M(m+m-) Pt(e+e-) Pt(m+m-) Invariant Mass and Pt Distributions for ZZ For 1 fb-1 data at ATLAS 13 events candidates Background free with current statistics ICHEP06, Zhengguo Zhao

  19. ATLAS signal background e-boost ANN Boosted Decision Trees (BDT) and Artificial Neural Network (ANN) ICHEP06, Zhengguo Zhao

  20. ANN Background efficiency BDT Signal efficiency Comparison of the efficiencies of BDT/ANN ICHEP06, Zhengguo Zhao

  21. Summary • ZZ, WZ and WW signals are expected to be established at CMS and ATLAS with 100pb-1~1fb-1 Expected signal and background with 1 fb-1 data at CMS/ATLAS • Anonymous gauge boson coupling can be probed with a few fb-1 data • To improve the TGC’s with LHC data, it’s crucial to build the TGCs into MC@NLO event generator ICHEP06, Zhengguo Zhao

  22. Backup Slides ICHEP06, Zhengguo Zhao

  23. Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Channels: ~ 108 Lcable: ~ 3000 km Muonspectrometer • s/pT ~ 2-7 % • |h| < 2.7, |h|<2.5 ( precision phys.) EM Calorimetry • s/E ~ 10%/√E(GeV)1% • |h|<3.2, |h| < 2.5 (fine granularity) Inner detector • s/pT ~ 0.05% pT(GeV) 0.1%; • |h| < 2.5 Central solenoid • 2 T Hadron Calorimeter • s/E ~ 50%/√E(GeV)3% • ||<3 ATLAS ICHEP06, Zhengguo Zhao

  24. EM calorimeter: • Lead tungstate • s/E = 5% / √E (GeV)  2% Muon spectrometer • DT+CSA+RPC Magnet solenoid 4 T Hadron Calorimeters • Barrel & Endcap: • Cu/Scintillating sheets • s/E = 65% /√E (GeV)5% Inner Detector: • Silicon pixels and strips ICHEP06, Zhengguo Zhao

  25. Triple Gauge Boson Couplings Open window to electroweak symmetry breaking mechanism LHC: orders of magnitude Improvement over LEP/Tevatron Expected 95% C.L. constrains contours (outer-> inside): (14TeV,100fb-1), (28TeV,100fb-1), (14TeV,1000fb-1), (28TeV, 1000fb-1) ICHEP06, Zhengguo Zhao

  26. Quartic Gauge Boson Couplings 100fb-1 6000fb-1 100fb-1 6000fb-1 ICHEP06, Zhengguo Zhao

  27. Systematic uncertainties on cross section Systematic uncertainties on significance Systematic Uncertainties (CMS) WZ ZZ ICHEP06, Zhengguo Zhao

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