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Di-Boson Production at Hadron Colliders

This seminar discusses the production of two gauge bosons at hadron colliders, including the Standard Model and beyond, the Tevatron and the LHC. Topics covered include gg, Wg, Zg, WW, WZ, ZZ, and Wh production, as well as the Higgs boson and its decay.

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Di-Boson Production at Hadron Colliders

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  1. Di-Boson Production at Hadron Colliders • The Standard Model and Beyond • Tevatron and the LHC • gg • Wg and Zg • WW, WZ, ZZ • Wh • Summary and Outlook Beate Heinemann, University of Liverpool Northwestern University - Seminar Oct. 4th 2004

  2. Di-Boson Production: What’s that? Associated production of ≥ 2 gauge bosons of electroweak interaction pp->gg, Wg, Zg, WW, WZ, ZZ + X ? Something happens Beate Heinemann - Northwestern University

  3. The Standard Model of Particle Physics • 3 generations of quarks and leptons interact via exchange of gauge bosons: • Electroweak SU(2)xU(1): W, Z, g • Strong SU(3): g • Symmetry breaking caused by Higgs field • Generates Goldstone bosons • Longitudinal degrees of freedom for W and Z • 3 massive and one massless gauge bosons Gauge Bosons Higgs Boson • Vacuum quantum numbers (0++) • Couples to mass Beate Heinemann - Northwestern University

  4. The Higgs boson: what do we know? mW depends on mt and mh • Precision measurements of • MW =80.412 ± 0.042 GeV/c2 • Mtop=178.0 +- 4.3 GeV/c2 • Prediction of higgs boson mass within SM due to loop corrections • Most likely value: 114 GeV • Direct limit (LEP): mh>114.4 GeV Beate Heinemann - Northwestern University

  5. The Higgs boson: what do we know? • Precision measurements of • MW =80.412 ± 0.042 GeV/c2 • Mtop=178.0 +- 4.3 GeV/c2 • Prediction of higgs boson mass within SM due to loop corrections • Most likely value: 114 GeV • Direct limit (LEP): mh>114.4 GeV Better prediction with expected improvements on W and top mass precision Beate Heinemann - Northwestern University

  6. Higgs Production: Tevatron and LHC Tevatron LHC Dominant Production: gg-> H, subdominant: HW, Hqq Beate Heinemann - Northwestern University

  7. Higgs boson decay • Depends on Mass • M<130 GeV: • bb dominant • tt subdominant • gg used at LHC • M>130 GeV • WW dominant • ZZ cleanest => di-boson decays most promising! Beate Heinemann - Northwestern University

  8. What if there is no Higgs? • WLWL cross section would violate unitarity since amplitude perturbative expansion in energy (s): s~s2/v2 + s4/v4… • Need either a Higgs boson with mh<1 TeV or some new physics (e.g. SUSY, Technicolor) • Tevatron and LHC probe relevant scale of 100 GeV - 1 TeV! => We will find something (higgs or more extraodinary) in the next 10 years! Beate Heinemann - Northwestern University

  9. Why not the Standard Model? Hierarchy problem: mh<<mPl  new physics at TeV scale Most Dark Matter in our universe unaccounted for No unification of forces …+ many more What is beyond the Standard Model? Supersymmetry (SUSY): rather complex (>100 parameters) Extra Dimensions Techni- and Topcolor Little Higgs Extended Gauge Groups or Compositeness: Z’, excited fermions, leptoquarks, … Beyond the Standard Model • New particles heavy  • At high energy colliders • Direct production • Indirect contributions Beate Heinemann - Northwestern University

  10. Tevatron Run II • Upgrade completed in 2001 • Accelerator: • Experiments CDF and D0: • New tracking systems • New RO electronics+trigger • Many other substantial new components and upgrades • Data taking efficiency>85% • Will mostly focus on CDF but show also some D0 results Beate Heinemann - Northwestern University

  11. Tevatron Performance ∫ Ldt= 680 pb-1 Max. L=1.03x1032 cm-2 s-1 Beate Heinemann - Northwestern University

  12. Tevatron Performance ∫ Ldt= 680 pb-1 Max. L=1.03x1032 cm-2 s-1 Beate Heinemann - Northwestern University

  13. Tevatron: Expected Performance Beate Heinemann - Northwestern University

  14. Beyond the Tevatron: LHC • pp-collider at CERN • Center-of-mass energy: 14 TeV • Starts operation in 2008 • 3 years “low” luminosity: 10 fb-1 /yr • High luminosity: 100 fb-1 /yr Beate Heinemann - Northwestern University

  15. Di-Boson Production: Why? • SM precision tests • SUSY • Large Extra Dimensions • Higgs • Run I anomalies ? Something happens Precision of Run I measurements limited Beate Heinemann - Northwestern University

  16. Di-Photon Production • SM couplings small • Ideal for New Physics Searches: • Large Extra Dimensions: • Graviton exchange? • Present sensitivity about 900 GeV • Run II: sensitivity about 2 TeV • Higgs ->gg: • BR small in SM 9but discovery channel at LHC) • Enhancements predicted in some BSM theories (“bosophilic Higgs”) • Extraodinary events with 2 photons and transverse momentum imbalance(?) G, h G Example LHC signal (CMS: 3 yrs) Beate Heinemann - Northwestern University

  17. Di-Photon Cross Section • Select 2 photons with Et>13 (14) GeV • Statistical subtraction of BG (mostly p0) • Data agree well with NLO • PYTHIA describes shape (normalisatio off by factor 2) Mgg (GeV) DFgg Beate Heinemann - Northwestern University

  18. Randall-Sundrum Graviton • Analysis: • D0: combined ee and gg • CDF: separate ee, mm and gg • Data consistent with background • Relevant parameters: • Coupling: k/MPl • Mass of 1st KK-mode • World’s best limit: • M>785 GeV for k/MPl=0.1 345 pb-1 Beate Heinemann - Northwestern University

  19. Some extensions of SM contain Higgs w/ large B(H) Fermiophobic Higgs : does not couple to fermions Topcolor Higgs : couples to only to top (i.e. no other fermions) Important discovery channel at LHC Event selection 2 Isolated ’s with pT > 25 GeV ||<1.05 (CC) or 1.5<||<2.4 (EC) pT () > 35 GeV (optimised) BG: mostly jets faking photons Syst. error about 30% per photon! Estimated from Data D0: Non-SM Light H ∫Ldt=191 pb-1 Central-Central Central-Forward Beate Heinemann - Northwestern University

  20. Non-SM Light Higgs H Perform counting experiments on optimized sliding mass window to set limit on B(H) as function of M(H) Beate Heinemann - Northwestern University

  21. gg+X: more exclusive channels • Run I: • found 1 event with 2 photons, 2 electrons and large missing Et • SM expectation 10-6 (!!!) • Inspired SUSY model where SUSY is broken at low energies: “Gauge Mediated Symmetry Breaking” • Run II: • Any new such event would be exciting! Beate Heinemann - Northwestern University

  22. GMSB: gg+Et • Assume c01 is NLSP: • Decay to G+g • G light M~O(1 keV) • Inspired by CDF eegg+Et event • D0 (CDF) Inclusive search: • 2 photons: Et > 20 (13) GeV • Et > 40 (45) GeV ~ ~ Beate Heinemann - Northwestern University

  23. NOT in SM SM Theory of W/Z+g Production Tree-level diagram of Tree-level diagram of These diagrams interfere and decay products are detected in the detector Beate Heinemann - Northwestern University

  24. Anomalous Couplings Existence of WWg vertex indirectly seen at LEP • LEP results hard to beat but complementary: • higher energy • WWg vs WWZ Beate Heinemann - Northwestern University

  25. Wg, Zg: beyond the Standard Model • Any anomalous couplings: • Increase in cross-section • Excess of events in high Etg region • Physics beyond SM (e.g. excited W/Z,excited e): • Increase in cross-section • Excess of events in high Etg region • Excess of events in high 3 body Mass region Beate Heinemann - Northwestern University

  26. W+ Results Combined: s*BR=18.1  1.6(stat)  2.4(sys)  1.2(lumi) pb SM: 19.3±1.4 pb Beate Heinemann - Northwestern University

  27. Z Results Combined: s*BR=4.6 ± 0.5(stat) ± 0.2(sys) ± 0.3(lumi) pb SM: 4.5±0.3 pb Beate Heinemann - Northwestern University

  28. Ratio of Cross Sections • Inclusive W and Z production: • Recent CDF result (hep-ex/0406078) • s(Z)xBR(Z->ll) / s(W)xBR(W->lv) =10.150.21% • Wg and Zg Production for Et>7 GeV: • s(Zg)xBR(Z->ll) / s(Wg)xBR(W->lv) = 4.6/18.1 = 25+-5 % => Expected due to • interference of t-, u-, and s-channel diagrams in Wg • No s-channel diagram in Zg => no interference =>Indirect Evidence for WWg vertex! Beate Heinemann - Northwestern University

  29. Photon Et • Data agree well with SM • Will be used to extract WWg and ZZg couplings Beate Heinemann - Northwestern University

  30. Mass • Data agree well with prediction: no sign of any signal of high mass • Can be used to constrain e.g. W* and Z* Beate Heinemann - Northwestern University

  31. WW: Why? • Never observed at hadron colliders with any significance (run 1: 5 observed / 1.2+-0.3 BG) • SM test • Higgs -> WW Beate Heinemann - Northwestern University

  32. WW Cross Section Beate Heinemann - Northwestern University

  33. WW: Decay Channels Beate Heinemann - Northwestern University

  34. WW: Cross Section Results • 2 independent analysis (high purity vs high acceptance) =>Consistent results • First significant signal: significance>3s • Agree with theor. prediction: sNLO = 12.5+-0.8 pb Beate Heinemann - Northwestern University

  35. WW Candidate Event Beate Heinemann - Northwestern University

  36. WW kinematic distributions • Kinematic properties as expected from SM WW production • => use the data to constrain new physics Beate Heinemann - Northwestern University

  37. H  WW(*)  l+l-nn • Higgs mass reconstruction not possible due to two neutrions: • Dilepton mass lower for h->WW: mass dependent cut • Employ spin correlations to suppress WW background: • leptons from h  WW(*)  l+l-nn tend to be collinear Higgs of 160 GeV Higgs of 160 GeV Beate Heinemann - Northwestern University

  38. H  WW(*)  l+l-nn • Similar analysis by D0 • Neither CDF nor D0 see any evidence for h production => set upper limit on cross section • Expect 0.11 events for 160 GeV SM Higgs with 200/pb Excluded cross section times Branching Ratio at 95% C.L. Beate Heinemann - Northwestern University

  39. WZ and ZZ • Select 2 leptons with M(ll) in Z mass range and • 2 leptons (ZZ->llll) • 1 lepton and Et (WZ->lll) • Significant Et (ZZ->ll) Expect 5.0+-0.6 events Observe 4 events  s<13.9 pb @ 95% C.L. NLO: s=5.2±0.4pb Beate Heinemann - Northwestern University

  40. WZ/ZZ: kinematics • Consistent with expectation • More data needed! Beate Heinemann - Northwestern University

  41. WZ/ZZ and Wh Production • Large backgrounds from QCD processes: W+jets, Z+jets • Use h->bb channel for Higgs search • WZ->Wbb will be observable before seeing the higgs=> excellent calibration channel • Exercises mass resolution: combining calorimeter and tracking => 30% improvement in energy resolution RunI:0.5-1% Beate Heinemann - Northwestern University

  42. Wh Production: Run 2 data • Selection: • W(mn or en) • 2 jets: 1 b-tagged • Search for peak in dijet invariant mass distribution • No evidence yet for WZ or Wh mbb (GeV/c2) Beate Heinemann - Northwestern University

  43. Summary of CDF Higgs Searches Beate Heinemann - Northwestern University

  44. Higgs Discovery at Tevatron? 2009 2006 NOW Beate Heinemann - Northwestern University

  45. Higgs Discovery at the LHC? fb-1 1 year @1034 1 year @1033 time 1 month @1033 LHC: ATLAS Values for single experiment Beate Heinemann - Northwestern University

  46. Summary and Outlook • Diboson Production excellent probe for New Physics • Higgs production • SUSY • Large Extra Dimensions • Precision test of SU(2)xU(1) gauge structure • Many new results from Tevatron • Machine and experiments running great! • Have got 2x more data on tape! • Anticipate 1.5-2 fb-1 by 2007 and 4.4-8.6 fb-1 by 2009 • Crucial for Higgs discovery at both Tevatron and LHC Cross Section (pb) Beate Heinemann - Northwestern University

  47. Backup Slides

  48. CDF: COT Aging Problem Solved! Beate Heinemann - Northwestern University

  49. Silicon Performance See talk by R. Wallny Beate Heinemann - Northwestern University

  50. CDF: B-tagging and tracking Beate Heinemann - Northwestern University

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