Higgs searches at LHC Higgs searches at LHC SM Higgs discovery - - PowerPoint PPT Presentation

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Higgs searches at LHC Higgs searches at LHC SM Higgs discovery - - PowerPoint PPT Presentation

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Higgs searches at LHC Higgs searches at LHC SM Higgs discovery potential SM Higgs parameters MSSM Higgs discovery potential Giovanna Davatz, ETH Zurich On behalf of the ATLAS and CMS collaborations April 5th 2006, LISHEP

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

Higgs searches at LHC Higgs searches at LHC

Giovanna Davatz, ETH Zurich On behalf of the ATLAS and CMS collaborations

April 5th 2006, LISHEP conference, Rio de Janeiro

  • SM Higgs discovery potential
  • SM Higgs parameters
  • MSSM Higgs discovery potential
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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

SM Higgs production processes at LHC

  • M. Spira et al. NLO

Most important for SM Higgs discovery: gluon fusion and vector boson fusion (VBF) VBF ≈ 10% of gluon fusion for mH < 200 GeV, comparable at mH 1TeV

LHC

Gluon fusion Vector boson fusion

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

Higgs decays: Branching ratios

Djouadi, Kalinowski, Spira

mH below 130 GeV: decay to bb dominates, But too large QCD background → no hope to trigger /extract fully hadronic final states → Look for final states with l (l=e,µ), γ Large mH: decay almost entirely through WW and ZZ

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

Discovery Potential of SM Higgs at LHC

Main discovery channels: 100 GeV < mH < 150 GeV: H → γγ, H → ZZ (*) → 4l, ttH → lbb+X, qqH → ττ 150 GeV < mH < 180 GeV: H → WW (*) → 2l2v Above 180 GeV: H → ZZ and H → WW channels LEP and el.mag. fits consistent with SM Higgs mass: 114.4 GeV < mH < 175 GeV @ 95% CL (new top mass

Tevatron)

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

  • Clear resonance: very good mass resolution!
  • background can be fitted from sidebands
  • Experimental challenge: lepton mass

resolution, rejection of non isolated leptons (tt, Zbb backgrounds)

  • golden channel!

H →ZZ(*) →4l

mH 130 GeV mH 150 GeV mH 170 GeV

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

H→γγ

  • Promising signature for Higgs boson mass region mH < 150

GeV

  • Rare decay channel: BR ~ 10-3
  • Large background S/B ≈ 1:20

– Reducible background (fake photons from jets and isolated π0) – Irreducible background (prompt photons)

  • Requires excellent energy resolution and knowledge of primary

vertex

  • Background can be estimated from side bands
  • Very good mass resolution of 1% expected

K-factors for signal and background included

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

H→WW(*) →2l2v

  • BR (H → WW) ≈ 1 for mH ~ 160 GeV (dip in the H → ZZ* sensitivity)
  • signature: 2 leptons plus high missing energy
  • Challenge: no narrow mass peak can be reconstructed

→ need good signal over background ratio, understanding of background

  • Large backgrounds WW, tt, Wtb significantly reduced by cuts on

(i) Lepton angular correlation (ii) Jet veto: no jet activity in central detector region

(Dittmar & Dreiner 1997)

Signature leads to good signal/background ratio →New: For the first time full detector analysis and detailed studies of background uncertainties performed.

Higher order corrections for signal and important background included

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

H→WW(*) →2l2v

Result: signal over background ratio >1 for a large mass range, luminosity needed to detect Higgs in this channel (from 150 to 180 GeV): < 10 fb-1 For mH 165 GeV discovery with already 1fb-1 → discovery possible very soon after LHC starts!

VERY PROMISING! CMS

Very recently study with full systematics and detector simulation performed (CMS Note 2006/047):

pt lep max signal /background discovery potential

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

Higgs Search in Vector Boson Fusion

Motivation: Increase discovery potential Improve measurement of Higgs boson parameters (couplings to bosons, fermions) (proposed by D. Zeppenfeld et al. ) Distinctive Signature of:

  • two high pT forward tag jets
  • little jet activity in the central region

⇒ central jet veto

Forward jets are the “signature” of VBF

Central jet veto effective for QCD background rejections, in particular against the inclusive tt production (common background for all VBF channels) Study should be repeated with full simulation and systematics

Jet Je t Pseudorapidity of jets Difference in pseudorapidity

φ η

Tag jets Higgs

Higgs QCD QCD Higgs

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

Higgs mass > 200 GeV

Most important SM Higgs channels: 200 GeV < mH < 700GeV: Inclusive H→ZZ, H→WW, leptonic decays mH > 700GeV: qqH → ZZ → 2l2v qqH → WW → 2l2j

for high mass: decreasing sigma → good signatures from llqq and llνν final states

Large width

Background: ZZ (/ WW) Z (W) + jets (neutrinos in jets or cracks in detector) (tt → WbWb) Better understanding of background when data available

qqH → WW → 2l2j

ATLAS

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Discovery Potential for SM Higgs CMS and ATLAS

Full mass range can already be covered a few years after start of LHC

Combined Atlas and CMS: full mass range with already 10fb-1

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

Determination of Higgs boson parameters

1.Mass

Higgs boson mass can be measured with a precision of <1% over entire SM mass range → in H→γγ and H → ZZ → 4l resonances (ultimately 0.1%)

  • 2. Coupling to bosons and fermions

coupling measurements from various channels: gg → H, qq → qqH and others.

Relative couplings can be measured with a precision of 10-20% (for 300 fb-1)

  • 3. Higgs self-coupling

Possible channel: gg → HH → WW WW → lv jj lv jj Small signal cross sections, large backgrounds from tt, WW, WZ, WWW, tttt, Wtt,... ⇒ so far, no significant measurement known at the LHC, sensitivity possible at SLHC

  • 4. Spin

Angular distributions in the decay channel H → ZZ(*) → 4l are sensitive to spin and CP eigenvalue. Needs large statistics

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

MSSM Higgs search

Two Higgs doublets model: 5 physical states 2 free parameters → common choice:

  • tanβ - ratio of vacuum expectation values of the two

doublets

  • mA- mass of pseudo-scalar Higgs boson

MSSM neutral Higgs bosons (LEP) –Mh, MA>92.9, 93.3 GeV @95% CL –MH± >89.6 GeV @95% CL for BR(MH± → τv) =1 –MH± >78.6 GeV @95% CL for any BR

  • 2 CP-even neutral Higgs bosons

h0, H0

  • 1 CP-odd neutral Higgs boson

A0

  • 2 charged Higgs bosons

H±

At high MA the heavy bosons degenerate in mass while the h does not go above a limit value of around 130 GeV

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MSSM Higgses: H,A

Production: mainly through gg → H/A, gg/qq → bbH/A Decay: Decoupling regime: High mA

  • decays to ττ:

analyse leptonic and hadronic channels!

  • decays to µµ: lower BR,

but better mass resolution Low tanβ regime: tanβ<5-10

  • transition region between

couplings to u- and d-type

  • use A→ZH, H → Wh,

H/A → tt for very low tanβ Intense coupling regime: Low mA, high tanβ

  • Higgses are almost degenerated

5σ discovery reach

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MSSM Higgses: H ±

Production:

  • for low mass: tt→tbH±
  • for high mass:

gg → t(b)H± qq’ → H± gg → H±H± gg → W±H± Decay:

  • for mH>~130GeV:

H± → t(*)b, dominates, but large background (tt+jets)

  • interesting for analyses:

H± → τν Reconstruction of the top decay and of the hadronic tau. tt and Wt backgrounds suppressed exploiting spin correlations

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Higgs at LHC, LISHEP 2006 Giovanna Davatz, ETH Zurich

MSSM Higgses: h

Decoupling regime High mA Decay:

  • h is SM-like (mh<135GeV!)

Low tanβ regime tanβ<5-10 Decay:

  • h-couplings to WW/ZZ and u-type

suppressed → bb, ττ ,γγ decays Large parts of the plane covered VBF modes are important In decoupling limit (high MA), the h behaves like a SM Higgs boson

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MSSM Higgs boson discovery

mh < 135 GeV/c2 mA ≈ mH ≈mH± at large mA Here only SM-like h

  • bservable if SUSY

particles neglected.

Plane fully covered (2x30 fb-1) 1 or more Higgs bosons can be observed → chance to disentangle SM / MSSM Main channels: h → γγ, tth → ttbb A/H → ττ, µµ H± → τν, tb

Assuming Susy particles are heavy

5σ contours

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Conclusion

agradecimentos aos organizadores pelo evento muito legal!

  • Standard Model Higgs detectable with O(10 fb-1) over entire mass range
  • In some channels discovery possible already with less than 5 fb-1!
  • If discovered need to study Higgs parameters (mass, spin, CP, couplings, ..)
  • MSSM plane coverage requires few tens of fb-1 in a maximal mixing scenario
  • VBF important for the SM and MSSM Higgs discovery