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Studies of Diboson Production and Triple Gauge Boson Couplings

Studies of Diboson Production and Triple Gauge Boson Couplings. Zhengguo Zhao University of Michigan, Ann Arbor, USA 9 th ACFA Physics and Detector Workshop& ILC GDE Meeting Feb. 4-7, 2007, Beijing. Outline. Introduction Recent Tevatron results Effort from ATLAS/CMS Summary.

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Studies of Diboson Production and Triple Gauge Boson Couplings

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  1. Studies of Diboson Production and Triple Gauge Boson Couplings Zhengguo Zhao University of Michigan, Ann Arbor, USA 9th ACFA Physics and Detector Workshop& ILC GDE Meeting Feb. 4-7, 2007, Beijing Beijing, Zhengguo Zhao

  2. Outline • Introduction • Recent Tevatron results • Effort from ATLAS/CMS • Summary Beijing, Zhengguo Zhao

  3. Introduction Beijing, Zhengguo Zhao

  4. V1 V3 V2 q V1 q V2 V1 q q’ q q’ V2 Diboson Production at Hadron Collider • LO Feynman diagram, V1, V2, V3 = Z, W, gWW, ZW, ZZ, Wg. • Production cross section predictable • Only s channel has three boson vertex, which manifest the gauge boson coupling SM: • Pure neutral vertexes ZZZ, ZZg are forbidden (Z/gcarry no charge and weak isospin that needed for gauge bosons couple) • Only charged couplings WWg, WWZ are allowed Beijing, 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 Beijing, Zhengguo Zhao

  6. l n  l W q W q’ l+ l- Z  l Production of WZ, WW • s-channel dominates, • Sensitive only to WWZ coupling • Clean signal eee, eem, mme, mmm • 3 isolated high pT leptons with large ET(miss) s-channel Sensitive to WWZ and WWg • Clean signal ee, mm,em • 2 isolated high pT leptons with opposite charge and large missing ET s-channel t-channel Beijing, Zhengguo Zhao

  7. l+ l- l’+ l’- q q’ qbar Production of Wg, ZZ • Isolated high pT lepton (e, m) large missing ET • Isolated g • Main bkg: W+jet, Z+ g • s channel suppressed by O(10-4) • Only t-channel at tree level, • 4 isolated high pT leptons from the Z pair decays • Clean signal eeee, eemm, mmmm, almost bkg free z z Beijing, Zhengguo Zhao

  8. H ZZ Diboson as background for searches Beijing, Zhengguo Zhao

  9. Motivations •Measure diboson production  and TGCs • Explore none-Abelian SU(2)U(1) gauge structure of 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 Beijing, Zhengguo Zhao

  10. Recent Results from Tevatron Beijing, Zhengguo Zhao

  11. Experiments at Tevatron Beijing, Zhengguo Zhao

  12. CDF & D0 Detectors CDF Run II Upgrades: New Silicon Vertex Detector (SVX) and faster tracking drift chamber (COT) New scinitllating-tile end-plug calorimeters Increased ηφ coverage for muon detectors New Scintillator Time-Of-Flight system D0 Run II Upgrades: New silicon (SMT) and Fiber (CFT) trackers, placed in new 2T Solenoid Calorimeters supplemented with Preshower detectors Significantly improved Muon System Beijing, Zhengguo Zhao

  13. Beijing, Zhengguo Zhao

  14. WW Production at Tevatron Beijing, Zhengguo Zhao

  15. WW+WZlnjj • 1 lepton with pT>25GeV, ET>25 GeV • ≥2 jets with pT > 15 GeV (WW+WZ) < 36 pb @ 95% CL Beijing, Zhengguo Zhao

  16. WW+WZlnjj anomalous coupling from CDF • Select 56 < mjj < 112 peak region • Minimize likelihood for pT of W(l,ET) -0.51 <  < 0.44, -0.28 < l < 0.28 Beijing, Zhengguo Zhao

  17. l n W q W q’ l+ l- Z WZ  lnll • 3 leptons (e, m) - CDF: pT(leading) >20 GeV, pT(others) > 10 GeV - D0: pT(all) > 15 GeV • m(l+l-) within mZ window • ET is used to suppress the bkg of Z+jet/g Beijing, Zhengguo Zhao

  18. WZ  lnll results Beijing, Zhengguo Zhao

  19. WWZ Anomalous Coupling For L = 300 pb-1 data, expect 2 signal and 1 background events. Observed 3 events. TGCs are determined to be Beijing, Zhengguo Zhao

  20. (Wglng) from D0 Beijing, Zhengguo Zhao

  21. Tevatron Results on Dibson Studies Tevatron results consistent with SM prediction Beijing, Zhengguo Zhao

  22. Diboson Studies from ATLAS and CMS Beijing, Zhengguo Zhao

  23. 4.5 km The LHC Experiments Beijing, Zhengguo Zhao

  24. Bunch Proton Parton (quark, gluon) l e + l Higgs e - Particle Z o e + Z o jet jet SUSY..... e - Collisions at the LHC 2804 bunch/beam 7 + 7 TeV separation: 7.5 m (25 ns) 40 MHz crossing rate 1011 proton / bunch 109 pp collision/s (superposition of 23 pp interactions per bunch crossing: pile-up) N = L × (pp) = 109 • Mostly low pt events (soft) events • Interesting high pt events are rare • New physics rate ~ 0.00001 Hz  event selection: 1 in 10,000,000,000,000 Beijing, Zhengguo Zhao

  25. Muon spectrometer • air-core toroids, MDT+RPC+TGC • s/pT ~ 2-7 % • |h| < 2.7, |h|<2.5 ( precision phys.) Length: ~ 46 m Radius : ~ 12 m Weight : ~ 7000 tons Channels: ~ 108 Lcable: ~ 3000 km EM Calorimetry • Pb-LAr • s/E ~ 10%/√E(GeV)1% • |h|<3.2, |h| < 2.5 (fine granularity) Inner detector • Si pixels and strips • Transition Radiation Detector (e/ separation) • s/pT ~ 0.05% pT(GeV)0.1%; • |h| < 2.5, B=2 T(central solenoid) Hadron Calorimeter • Fe/scintillator (central), Cu/W-LAr (fwd) • s/E ~ 50%/√E(GeV)3% • ||<3 Beijing, Zhengguo Zhao

  26. 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 Beijing, Zhengguo Zhao

  27. 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) Beijing, Zhengguo Zhao

  28. 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) Beijing, Zhengguo Zhao

  29. 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 Beijing, Zhengguo Zhao

  30. 2.1% 7.7% 47.4% 42.9% ZW Signal and Backgrounds(ATLAS) (for 1 fb-1 data) Beijing, Zhengguo Zhao

  31. 2.6% 3.4% 8.3% 47.3% 38.4% WW Signal and Background (ATLAS) (for 1 fb-1 data) Beijing, Zhengguo Zhao

  32. 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 Beijing, Zhengguo Zhao

  33. ANN Background efficiency BDT Signal efficiency Comparison of the efficiencies of BDT/ANN Beijing, Zhengguo Zhao

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

  35. 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 Beijing, Zhengguo Zhao

  36. 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 Beijing, Zhengguo Zhao

  37. 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 • ZZ: ~1 fb-1 • WZ: ~150 pb-1 Beijing, Zhengguo Zhao

  38. Summary • D0 and CDF have been actively studies diboson production and the corresponding TGCs. The results so far are consistent with SM predictions. • WZ, WW and ZZ signals are expected to be established at CMS and ATLAS with 100pb-1~1fb-1 • Anomalous gauge boson coupling can be probed with a few fb-1 data • Advanced techniques (BDT, ANN) can significantly improve the S/B. • To improve the TGCs with LHC data, it’s crucial to correctly build the TGCs into MC@NLO event generators Beijing, Zhengguo Zhao

  39. 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 Beijing, Zhengguo Zhao

  40. LHC Tevatron Diboson Production Cross Section Beijing, Zhengguo Zhao

  41. Boosted Decision Trees (BDT) and Artificial Neural Network (ANN) ATLAS e-boost ANN Beijing, Zhengguo Zhao

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