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Higgs hunting: the basics Run I Higgs searches MSM prospects for Run II Conclusions

Higgses at the Tevatron: Status and Prospects Peter Ratoff Lancaster University representing the CDF and DØ Collaborations. Higgs hunting: the basics Run I Higgs searches MSM prospects for Run II Conclusions. MSM Higgs mass constraint: experiment. Direct Searches -combined LEP data

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Higgs hunting: the basics Run I Higgs searches MSM prospects for Run II Conclusions

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  1. Higgses at the Tevatron: Status and ProspectsPeter RatoffLancaster Universityrepresenting the CDF and DØ Collaborations Higgs hunting: the basics Run I Higgs searches MSM prospects for Run II Conclusions

  2. MSM Higgs mass constraint: experiment • Direct Searches -combined LEP data • MH > 107.7 GeV (95%CL) • Fits to precise EW data (LEP EWWG) • MH = 76-38+68 GeV • MH < 188 GeV (95%CL) Moriond Electroweak 2000

  3. Higgs mass constraints: theory • MSSM requires • MH 125 - 130 GeV • Any weakly coupled SUSY theory requires MH200 GeV • The MSM requires • 130  MH  180 GeV • Vacuum stability  lower bound • Landau pole  upper bound • Probing the MSM Higgs up to ~ 180 GeV has profound implications for the scale of any new physics,  Riesselmann, hep-ph/9711456

  4. MSM Higgs production cross-sections Gluon fusion dominates but WH/ZH production more accessible ... Gluon fusion Associated production WH or ZH

  5. MSM Higgs decay branching ratios • For MH 135 GeV • H0  dominates … but rate falling rapidly • QCD background precludes gg  • For MH  135 GeV • Gauge boson decays dominate ( H0  WW )

  6. Tevatron: low mass Higgs searches For MH 135 GeV: use the same basic strategy as LEP … … study associated production of ZH and WH To the standard leptonic HZ channels add W  l  with H bb ... … the qqbb channel is very difficult as the QCD backgrounds are severe • Low mass Higgs sensitivity depends on • the integrated luminosity collected • b-quark jet tagging performance • mass resolution of reconstructed bb jets

  7. MSM Higgs searches in Run I CDF MSM Higgs searches (1998) ... … similar results from DØ for lbb

  8. MSSM Higgs searches in Run I Large bb cross-section at the Tevatron can be used to exploit enhanced Yukawa couplings ... e.g. Abb coupling  tan  cross-section  tan2  search for bb production where  = h, H, A • CDF searches for bbbb final states: • Trigger: 4 level-2 jets (>15 GeV) +  ET > 125 GeV • Offline: Mass-dependent jet ET selection

  9. Run I MSSM:  production limits Convert .BR limits into tan vs. Higgs mass exclusion region ...

  10. LEP vs. Tevatron MSSM limits For the most optimistic LEP performance scenario (Priorities for LEP in 2000 - P.Janot) … … the Tevatron beautifully complements LEP!

  11. Fermilab SUSY/Higgs Run II Workshop • Run II Physics Workshops throughout 1999 • Draft report from Higgs Working Group (67 authors) • http://fnth37.fnal.gov/higgs.html • Workshop goals • perform comprehensive survey of final states • study effect of improved b-tagging and bb mass resolution • determine integrated luminosity (as function of MH ) for • 95% CL exclusion (1.96) • 3 observation; Prob(bgnd) < 0.00135 • 5 discovery; Prob(bgnd) < 2.7 x 10-7 • Workshop conclusions included a few surprises: • effect of combining all search limits (like LEP) • effect of new channels not previously considered • The Tevatron Higgs reach had been underestimated !

  12. Run II : Coming March 2001 s 2.0 TeV Luminosity 21032 Ldt 2-30fb-1

  13. Working Group Studies • Simulation and analysis methods: • CDF fast detector simulation QFL’ • Generic ‘Tevatron detector’ simulation SHW with CDF Run I b-tag efficiencies • Neural network analysis (NN) in some cases • jet mass resolution • b-jet tagging

  14. jet mass resolution • Higgs discovery critically dependent on bb di-jet mass resolution • jet corrections depend on missing ET, muon momentum, jet charged fraction ... • other important effects: jet algorithm, ISR/FSR, pileup due to multiple ints … • can use Zbb jets for calibration ... CDF (Run I) Z before/after b-quark specific jet corrections

  15. b-jet tagging • Many algorithms possible … • illustrative example (DØ) :- • jet pT > 15 GeV •  3 tracks with large I.P.’s • 3D constrained vertex fit • in x-y plane require L/ > 3 • c-jet tags / b-jet tags  1/3 • udsg jet tags <1% (pT<70 GeV) • Much work still to do!

  16. Low mass MSM Higgs: 90-130 GeV • Working group studies concentrated on • WH  lbb 2 b-jets + isol l± + miss ET • ZH  bb 2 b-jets + large miss ET • ZH  l+l-bb 2 b-jets + 2 isol l± + MZ • WH/ZH  qqbb 2 b-jets + 2 non-b-jets • pp  ppH 2 b-jets + fwd pp • All channels combined for discovery potential

  17. WH  l • the single most powerful channel for Higgs discovery • main backgrounds: W , tt, single top (W*tb, gWtb), WZ • efficiency x BR(H )  2% MH = 110 GeV Effect of bb mass resolution QFL’ , 1 fb-1,30K PYTHIA WH / bin SHW, 10 fb-1, Significance = S/B

  18. ZH   / l+l- • main backgrounds: Zbb, tt, single top, ZZ, (Wbb, WZ), bb-dijets, ... • more difficult to separate bb backgrounds from signal ... • … very conservative treatment of QCD background (bb-dijets) ZH   / l+l- combined SHW, Neural network SHW

  19. High mass MSM Higgs: 130-200 GeV • Assoc. production with H  runs out at 130 GeV • how can the Tevatron Higgs reach be extended ? • … make use of the rising H  W W* branching ratio ! • exploit the large gg  H cross-section • identify final state topologies with small SM contribution • focus on leptonic Gauge Boson decays ... Excellent trigger topologies Less difficult QCD backgrounds Han, Turcot, Zhang

  20. MSM Higgs search: Tri-lepton channel • Cleanest signature ... • Associated production VHWWW(*) / ZWW(*) • Inclusive di-lepton trigger: • pt1 > 10 GeV, pt2 > 5 GeV • OR • inclusive high pt single lepton • Golden modes (like-sign, like-flavour leptons) • OR • tight kinematic cuts to deal with WZ/ZZ • Small rate: • limited sensitivity to MSM Higgs, but … • New Physics could  observable enhancements Baer + Wells (hep-ph/9710368)

  21. MSM Higgs search: Di-lepton + missing ET • inclusive production • HX WW(*)X ll ’’ X • leading contribution from gluon fusion channel ... • (ggH) x BR(HWW(*)) x BR(We,)2 •  7 - 14 fb in MH interval 140 - 190 GeV • SM backgrounds: • WW  ll ’’ 1090 fb • +-  l l ’’’ 23 pb • tt  bl bl ’’ 722 fb • WZ, ZZ, tW ~220 fb •  Background  25 pb  S/B ~ 4 x 10-4 Han, Turcot, Zhang

  22. MSM Higgs search: Di-lepton + missing ET • Event selection:- • step 1: basic cuts (maintain high efficiency whilst reducing  and tt backgrounds •  bgnd  165 fb (mainly WW) • step 2: apply 6-variable Likelihood discriminant • step 3: background normalisation •  bgnd  106 fb (dominated by WW and W + fake (je) ) • step 4: final selection • exploit different kinematics of WW production • continuum vs. at threshold via a spin 0 resonance • utilise angular correlations between leptons and missing ET … the best chance to discover high mass MSM Higgs in RunII!

  23. MSM Higgs search: Di-lepton + missing ET Step 3: bgnd norml’n Step 4: final selection 10 fb-1 => 3.1% stat error on bgnd Higgs contamination : S/B ~ (3-5)% WW bgnd reduced by factor 40! ... clear excess from Higgs prod’n

  24. MSM Higgs search: like-sign di-lepton + jets • Distinct signature: l l jet jet X • standard New Physics search topology • Five contributions to consider • WH  WWW  l  l  j j • ZH  ZWW  l’l’l  j j • WH  WZZ  l  l’ l’ j j • WH  WZZ  l ll’ l’ j j • ZH  ZZZ  ll l’ l’ j j • Large number of SM backgrounds … • di-boson, tt, tri-boson, ttV, fakes, … • S/B larger than di-lepton + missing ET channel but smaller signal (x 3) • Bgnd systematic error larger ? Schmitt + Turcot Marciano, Stange, Willenbrock (PRD49, 1354 (1994))

  25. MSM Higgs: all channels • Bayesian combination: all channels and both expts (CDF/DØ): • assume 10% mass resolution • neural network analysis for H  channels • conservative treatment of QCD bgnd. for HZ   • systematic error: Min of 10% or 1/( L dt x B) • bands represent 30% effect from varying Mbb resol, b, bgnds 95% CL exclusion to ~ 185 GeV for 10 fb-1  3 observation to ~ 185 GeV for ~ 20 fb-1 5 discovery up to ~ 125 GeV for ~ 30 fb-1

  26. Run II Luminosity Prospects • Annual expectations:- • 2001-2 1 fb-1 per year (per expt) • 2003-5 2-3 fb-1 per year • 2005+ 5 fb-1 per year (until LHC overtakes) • Integrated luminosity by ~ • 2002 2 fb-1 • 2005 10 fb-1 • 2007 20 fb-1

  27. Conclusions • Strong experimental and theoretical motivation that the Higgs boson is within the reach of current accelerators • Run I Legacy: • MSM Higgs searches were luminosity limited • MSSM Higgs: interesting CDF limits for bb searches ... • … probed parameter space inaccessible to LEP • provided valuable experience for Run II • Run II Prospects: • the potential to cover most of the mass range preferred by the electroweak fits • use of H  WW(*) channels will significantly extend the Higgs mass reach • can test the validity of MSM up to Mplanck scale ! • MSSM Higgs opportunities (no time to discuss today!!)

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