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Search for the Higgs Boson at the LHC

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Micro-summary of the Higgs discovery potential at LHC on the occasion of ... Randall-Sundrum model: warped extra dimensions; two branes (Planck & TeV plane) ... – PowerPoint PPT presentation

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Title: Search for the Higgs Boson at the LHC


1
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
2
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
3
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)

4
SM Higgs experimental status
  • sxB(H-WW) for mH160GeV lt 5.7pb (D0), lt 5.6pb
    (CDF)

5
The SM Higgs _at_ LHC
  • Production

6
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)
7
SM Higgs low mass

8
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
9
SM Higgs intermediate mass
  • Decay modes to WW and ZZ become important

10
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
?
11
SM Higgs intermediate to high mass
  • The easy region high probabilityfor decays
    to ZZ()

12
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
13
SM Higgs summary
  • Full range of Higgs boson masses can be covered -
    most of it already at low luminosity

14
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!

15
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

16
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

17
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

18
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
19
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

20
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
21
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!
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