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Young-Kee Kim University of California, Berkeley (LBNL / Fermilab) CDF Experiment

Studying EWSB at the Tevatron (Lecture #3). Young-Kee Kim University of California, Berkeley (LBNL / Fermilab) CDF Experiment SLAC Summer Institute SLAC, Aug. 13 – 17, 2001. EW Measurements (last ~10 years). 1991 M top limit. M w (GeV). M H (GeV). 2001. 1991. 1995.

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Young-Kee Kim University of California, Berkeley (LBNL / Fermilab) CDF Experiment

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  1. Studying EWSB at the Tevatron (Lecture #3) Young-Kee Kim University of California, Berkeley (LBNL / Fermilab) CDF Experiment SLAC Summer Institute SLAC, Aug. 13 – 17, 2001

  2. EW Measurements (last ~10 years) 1991 Mtop limit Mw (GeV) MH (GeV) 2001 1991 1995 1s prediction year Mtop (GeV)

  3. Higgs • Standard Model 114 < MHiggs < 222 GeV • Precision Electroweak Measurements  favor light Higgs (MHiggs < ~222 GeV @95% CL) • Direct Searches for SM Higgs  MHiggs > 114 GeV @95% CL • 2s Hint @115 GeV Higgs • MSSM h0 • behaves very similar to SM Higgs • Mh0 < ~130 GeV Most of MSSM models • Possible to observe Higgs at the Tevatron if it is light.

  4. Light Higgs Searches u e- • If the light Higgs exists • Both Tevatron (2000 GeV pp collider) and LEP 2 (200 GeV e+e- collider) produce them. • But hard to observe • The Higgs coupling to stable matter is very small. • a low production rate • H  bb events are swamped by other processes. • a poor signal to background ratio • Strategies • Search for ZH or WH events. • e+e- Z*  Z H • u d  W+*  W+ H • A low production rate, but clean signature H H u e+ e- b ge H e+ b u b gu g u b

  5. Higgs Searches at LEP 2 (e+e- collider) M > 109 GeV 3.0 ZH, 3.6 bgrn, 6 observed e+e- ZH cross section (fb) e+e- cm energy (GeV) ~2s excess observed in agreement with MH ~ 115 GeV or MH > 114 GeV at 95% CL

  6. ZH Candidates at LEP 2 e+e-bb bb e+e-bb nn ALEPH L3

  7. Higgs Searches : LEP 2  Tevatron & girls LEP 2 Tevatron

  8. SM Higgs Decays

  9. Higgs Hunting at the Tevatron s(Higgs + X) vs MHiggs pb top gg  H  WW* WH ZH • gg  H  bb : too difficult • (swampt by QCD bgrnd) • MHiggs < ~135 GeV : • qq  W*  WH, qq  Z*  ZH • MHiggs > ~135 GeV : • gg  H  WW* H bb H  WW Dominant decay mode

  10. Higgs Hunting at the Tevatron (cont.) • T tt-bar + Higgs : Cross section very low (few fb) • but low signal/background s(Higgs + X) vs MHiggs pb H bb H  WW Major background : t t-bar + jets Dominant decay mode Tests top quark Yukawa coupling

  11. SM Higgs Signatures (Run I) b-tagging and Mbb resolution are critical for a light Higgs (see b tagging in Lecture #2)

  12. Mbb Resolution MC H  bb-bar CDF Run I : Z  bb-bar

  13. Run I : WH  ln + bb-bar

  14. Run I : WH, ZH  qq-bar + bb-bar

  15. Run I : ZH  nn-bar + bb-bar

  16. Run I : ZH  l+l- + bb-bar

  17. Run I Higgs Limits

  18. CDF b-tagged events

  19. Tevatron Higgs Potential (Luminosity Limited) Parameterized Simulation Run IIb Run IIa MHiggs (GeV) SM MSSM

  20. MSSM Higgs Searches

  21. MSSM Higgs Production @ Tevatron

  22. MSSM Higgs Branching Ratios

  23. Run I qq  bb-bar f  bb-bar bb-bar

  24. SUSY Higgs limits (b b decay) bb + h/H/A enhanced at large tanb bb + (h/A)  4b s ~ 1 pb for tanb = 30 & Mh = 130 GeV CDF Run I 3 b tags tan  = 35 170 GeV

  25. Run I Charged Higgs Searches

  26. Run I Charged Higgs Results

  27. Run I Bosophilic/Fermiophobic Higgs

  28. Run I Bosophilic Higgs Limits

  29. Searches for New Phenomena e.g. Large Extra Dimensions : search for Graviton exchange in the e+e- and gg Minv vs. cosq* distributions DØ No evidence for Extra Dimensions (ED). Set limits on the energy scale of extra dimensions: 1.0 TeV for ED=2 1.3 TeV for ED=7. signal region

  30. Direct Searches for SM & MSSM Higgs Particles

  31. Tevatron Run II Higgs Discovery Potential • Run IIa ~2fb-1 by 2003 • potential increase ~50 • we are at limit set by LEP 2 and should have a small number of WH or ZH candidates if MH ~ 115 GeV. • Run IIb ~15 fb-1 by ~2007 • We should have 3s coverage over most of mass range, MH < 180 GeV. ** MSSM predict Mh < 130 GeV

  32. spin ½ fermions spin 1 bosons

  33. Higgs : spin 0 boson

  34. Conclusions • The origin of mass  the Higgs boson • Indirect probe from precision Electroweak Measurements such as Mw, sin2qw, Mz, Mtop. • The Higgs boson is around the corner ! • Possible senarios in this decade • Discover Higgs bosons with MH < 130 GeV • Is this the Standard Model Higgs ? • If not, implies new physics • Discover Higgs bosons with MH > 130 GeV • Rules out some extensions of the Standard Model • Does it agree with Electroweak measurements ? • No discovery upto LHC • Detectable effects appear in the production rate and properties of W boson pairs at ~1 TeV. • Discover SUSY particles • Other new Phenomena • Whatever the outcome, • It will be extremely interesting. • At present, it is essentially an experimental question.

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