Search for the Higgs Boson at the LHC

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Search for the Higgs Boson at the LHC

• W. Adam
• Institut für Hochenergiephysik der ÖAW
• Micro-summary of the Higgs discovery potential at
  LHC on the occasion of

FAKT-Tagung, Weyer, 26./27. Sep. 2004
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SM Higgs experimental status

• The situation after LEP
• Indirect (full EW fit)
• Preferred valuemH 114 69 -45 GeV(exp.
  errors only)
• LimitmH lt 260 GeV _at_ 95CL
• Precise values might still change,
• but message is clear a light Higgs
• is favoured by the measurements.
• Direct (LEP searches)
• Observed (expected) limitmH gt 114.4 GeV
  (115.3GeV)
• preferred value from -2lnQ 115GeV

114GeV
129GeV
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SM Higgs experimental status

• News from the Tevatron
• Signatures HW?Wbb?(en)/(mn)bb,
  HW?Zbb?(ee/mm/nn)bb (mHlt130)
• gg?H?WW ?(en/mn)(en/mn) (mHgt130)
• s(WH) x B(H?bb) for mH115GeV lt 12.4 pb (D0,
  e-channel)
• lt 5 pb (CDF)

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SM Higgs experimental status

• sxB(H-WW) for mH160GeV lt 5.7pb (D0), lt 5.6pb
  (CDF)

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The SM Higgs _at_ LHC

• Production

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SM Higgs low mass

• Decay
• bb dominates, but high multi-jet backgrounds
  and low mass resolution
• gg BR low (10-3 to 10-4) - use small Higgs
  width and high resolution EM calorimetry

Material in front of calorimetry(e.g. CMS
full-Si tracker) will need to complement
withreconstruction of convertedphotons (under
study)
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SM Higgs low mass

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SM Higgs production via VBF

• Contributes 10 at low masses, dominates at very
  high masses
• Special topology allows for easy tagging
• Forward jets
• Central Higgs decay products
• Low mass analysis decay channels
• WW, tt and gg

Taus need trigger (leptons and narrow jets) and
offline enhancement (t-lifetime ? tracking)
Contribution of VBFanalysis to total significance
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SM Higgs intermediate mass

• Decay modes to WW and ZZ become important

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SM Higgs intermediate mass

• H?WW ? llX
• strong background from top decays
• need to use WW spin correlation
• veto on central jets

pT
For mH17010GeV 10 fb-1 are sufficient for
discovery
?
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SM Higgs intermediate to high mass

• The easy region high probabilityfor decays
  to ZZ()

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SM Higgs intermediate to high mass

• Golden channel H?ZZ ? 4m
• high energy muons
• Z mass constraint(s)
• irreducible background ZZ production

for high mass decreasing sigma - need more BR
use llqq or llnn
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SM Higgs summary

• Full range of Higgs boson masses can be covered -
  most of it already at low luminosity

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MSSM Higgs Boson

• 5 Higgs bosons (h,H,A,H)
• Usually parametrised using mA and tanb (tree
  level). Stop-mixing at loop level!
• Important difference to searches at previous
  experiments cascades via SUSY particles are
  possible!

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MSSM Higgs H, A

• Decoupling regime
• High mA, high tanb
• decays to tt high BR, analyse leptonicand
  hadronic channels!
• decays to mm lower BR, but 1 mass resolution
• Intermediate regime
• mAlt500GeV, tanblt5-10
• transition region between couplings to u- and
  d-type
• use A?ZH, H ? Wh, H/A ? tt for very low tanb
• Intense coupling regime
• Low mA, high tanb
• Higgses are almost degenerate

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MSSM Higgses h

• Decoupling regime
• High mA, high tanb
• h is SM-like (mhlt150GeV!)
• Intermediate regime
• mAlt500GeV, tanblt5-10
• h-couplings to VB and u-typesuppressed ? bb, tt
  decays
• Large parts of the plane covered
• VBF modes are important

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MSSM Higgses H

• Production
• for low mass t?bH
• for high mass gb ? tH qq ? H gg ?
  HH gg ? WH
• Decay
• for mHgt130GeV H ? t()b dominates
• interesting for analyses H ? tn

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MSSM Higgses cascade decays

• In the MSSM Higgs bosons can decay to SUSY
  particles and/or be producedin SUSY decay
  cascades.
• One scenario
• M2 2M1 350GeV, m 1TeV
• m(gluino) 1200GeV
• ms(squark) 800GeV
• long cascades via ?03,4 and ?01,2? mHlt200GeV
  accessible

N.Marinelli_at_PHLHC04
SUSY signal
SUSY bkg
SM bkg
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More exotic scenarios

• Still more Higgs bosons
• CP-violationCan add phases to MSSM parameters -
  major changes to all signatures
• Invisible decays, e.g. to LSPsexcess would be
  visible, but interpretation?
• Extra dimensionse.g. Radion decays to Higgs
  bosons
• Fermiophobic, gluophobic scenariosSpecific
  points in SUSY parameter space orin more general
  2HDM models
• Other scenarios
• Technicolorstill alive .. LHC could look for
  decays of rT to vector bosons.
• Strong VL-VL-couplingthe no-Higgs scenario
  look for resonant WZ and non-resonant WW
  scattering

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Radion decays

• Randall-Sundrum model
• warped extra dimensions two branes (Planck TeV
  plane)
• Radion scalar representation of the 5d
  gravitational field
• Most promising channel
• F?hh?ggbb look for mass peaks in the gg
  (narrow) and jj (broader) system
• Other channels studied ttbb, 4b

S.Gennai_at_PHLHC04
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Conclusions

• In the Standard Model
• LHC covers the full mass range
• If discovered need to measure parameters (mass,
  spin, CP, couplings, ..) major field of activity
• In the MSSM
• The light Higgs is detectable in the full range
• Some regions of parameter space are tricky
• Analyses looking for SUSY decay chains are being
  developped
• Whats about extensions? CP-violation?
• Substantial progress also on the theoretical
  side, e.g.
• KNNLO for the SM Higgs production
• full one-loop 2-loop RCs for large couplings in
  the MSSM
• Still quite some work to be done before LHC
  startup!