Higgs Physics at LHC

1
Higgs Physics at LHC
Andrey Korytov (for ATLAS and CMS
Collaborations)
ATLAS
CMS
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Introductory remarks

• Focus of the talk on the discovery reach
• Discovery statistical significance Sgt5
• Channels for which discovery is possible at
  Lintlt30 fb-1
• (2 yrs at low luminosity L21033 cm-2 s-1)
• Cross sections
• CMS NLO K-factors (dynamic K-factors for some
  analyses)
• ATLAS mostly LO (LO is often more conservative
  than NLO)
• CMS Physics Technical Design Report, v.II, is
  out in June
• First public presentation
• Full detector simulation and offline
  reconstruction
• Rigorous study of systematic errors for many
  analyses
• ATLAS relatively recent updates, where available

new
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SM Higgs discovery signatures at L30 fb-1

• Colored cells detailed studies available
• YES sure discovery in the appropriate range
  of masses at L30 fb-1

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Standard Model Higgs H?gg
new

• Backgrounds
• prompt gg
• prompt g jet(brem g, p0?g)
• dijet
• Analysis
• Cut-based
• PT, isolation, Mgg
• events sorted by em shower profile quality
• Optimized
• loose cuts and sorting
• event-by-event kinematical Likelihood Ratio
• bkgd pdf from sidebands, signal pdf from MC
• Systematic errors folded in

CMS
CMS dMgg lt 1
5
Standard Model Higgs H?WW?2l2n
Signal Region Control
Sample

• Backgrounds
• WW, tt, Wt(b), WZ, ZZ
• gg?WW (box)
• Analysis
• KNLO(pTWW)
• cuts
• e/m kinematics, isolation, jet veto, MET
• counting experiment, no peak
• background from a control sample
• signal 12ltmlllt40 GeV
• control sample memgt60 GeV
• reduce syst. errors pay stat. penalty
• systematic errors are folded in

new
CMS
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Standard Model Higgs H?ZZ?4l
new

• Backgrounds
• tt, Zbb, ZZ
• Analysis
• KNLO(m4l)
• cuts
• e/m kinematics, isolation
• cuts can be flat or m4l-dependent
• distinct m4l peak
• control samples
• sidebands (low statistics, shape is not trivial)
• Z-peak (Z and ZZ production are similar)
• muon reconstruction and isolation cut
  efficiencies derived from data
• full treatment of systematic errors

CMS H?4m
new
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Standard Model Higgs qqH, H?WW?2l2n
Signal Region Control
Sample
ATLAS MH160 GeV H?WW?e?

• Backgrounds
• tt, WWjj, Wt
• Analysis
• 2 high pT leptons MET
• 2 forward jets (b-jet veto)
• central jet veto
• counting experiment, no peak
• background from data
• Signal all cuts
• Control sample no lepton cuts
• Result
• better than inclusive WW (!!!)

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Standard Model Higgs qqH, H?tt

• Backgrounds
• Zjj, tt
• Analysis
• two forward jets, central jet veto
• two leptons (e, m, t-jet)MET
• tt ?lnn lnn
• tt ?lnn t-jet
• mass(l l or t-jet pTmis)
• despite 3 or 4 ns present, works quite well in
  collinear approximation

H?tt?em
ATLAS 30 fb-1
ATLAS
t
pTmis
H
t
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Difficult (impossible) channel ttH, H?bb
SM Higgs ttH, H?bb
ATLAS
30 fb-1

• CMS
• careful study of systematic errors in the Physics
  TDR
• syst error control at sub-percent level is needed
• does not appear feasible...

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Standard Model Higgs Summary
new
NLO cross sections Systematic errors included

• Benchmark luminosities
• 0.2 fb-1 exclusion limits will start carving
  into SM Higgs x-section
• 1 fb-1 discoveries become possible if MH170 GeV
• 10 fb-1 SM Higgs is discovered (or excluded) in
  full range

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MSSM Higgs bosons h, H, A, H

• SUSY stabilizes Higgs mass
• 2 Higgs field doublets needed
• Physical scalar particles h, H, A, H
• Properties at tree level
• fully defined by 2 free parameters MA, tanb
• CP-even h and H are almost SM-like in vicinity
  of their mass limits vs MA hmax and Hmin
• large tanb
• enhances coupling to down fermions
  b and t are very important!
• suppresses coupling to Z and W
• CP-odd A never couples to Z and W
• decays bb, tt (and tt for small tanb)
• H strongly couples to tb and tn
• all Higgs bosons are narrow (Glt10 GeV)
• Loop corrections
• gives sensitivity to other SUSY parameters
• mhmax scenario most conservative LEP limits

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MSSM Higgs boson h, H, A production
h H
A
tanb3
h H
A
tanb30

• x-sections are large, often much larger than SM
  (dotted line)
• bb(h/H/A) production is very important

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MSSM Higgs SM-like signatures

• CMS
• better detector simulation
• systematics included
• contours recessed

• ATLAS
• no systematics included

CMS 2003 CMS 2006
new
ATLAS
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MSSM Higgs heavy neutral H, A

• production in association with bb (especially
  good at large tanb)
• bb-decay mode (80) is overwhelmed with QCD
  background
• tt-decay mode (20) is the next best
• mm-decays (0.1) allow for direct measurement
  of G
• better detector simulation (i.e. more realistic)
  
• systematics included
• contours recessed (low MA band, qqH, moved to
  SM-like Higgs plot)

CMS 2003 CMS 2006
new
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MSSM Higgs H

• Heavy H (Mgtmt)
• production via gg ? tbH ? bjjbtn
• and gb ? tH ?
  bjjtn
• H ?tn (H ?tb overwhelmed by bkgd)
• t?Wb?jjb
• backgrounds tt, Wt, Wjets
• Light H (Mltmt)
• production via gg/qq ? tt ? btnbln
• t? Hb, H ?tn
• t?Wb?lnb
• backgrounds tt, Wt, Wjjj

new
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Difficult (impossible) channels
MSSM Higgs H?tb
MSSM Higgs bb(H/A), (H/A)?bb
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MSSM Higgs bosons h, H, A, H

• Special benchmark points
• max stop mixing (mhmax)
• mh lt 133 GeV
• MSUSY1 TeV
• most conservative LEP limits
• no mixing
• mh lt 119 GeV
• MSUSY1 TeV
• gluophobic h
• gg?h is suppressed (topstop loop cancellation)
• mh lt 119 GeV
• MSUSY350 GeV
• small aeff (mix h/H)
• tt and bb-decays suppressed
• even for large tanb
• mh lt 123 GeV
• MSUSY800 GeV

• Loop corrections give sensitivity to the rest of
  SUSY sector, more specifically to
• stop quark mixing Xt
• squark masses MSUSY
• gluino mass Mg
• SU(2) gaugino mass M2
• higgsino mass parameter m

Suggested by Carena et al. , Eur.Phys.J.C26,601(2
003)
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MSSM Higgs other benchmark points?

• ATLAS studies
• preliminary (no syst)
• vector boson fusion
• qq(h/H)
• h/H?tt, WW, gg
• caveat for small aeff decoupling from tt is
  compensated by WW enhancement
• all four special points are well covered at L30
  fb-1

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MSSM Higgs or SM Higgs?

• SM-like h only
• considerable area
• even at L300 fb-1
• Any handles?
• decays to SUSY particles?
• SUSY particle decays?
• measure branching ratios?

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MSSM Higgs or SM Higgs?

• Decays to SUSY
• h?c20c20?(2lc10)(2lc10)
• Signature
• Four leptons
• Large MET

• BR for different channels
• R BR(h?WW) / BR(h?tt)
• DRMSSM-RSM/sexpimental

Msleptons250 GeV
ATLAS 300 fb-1
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MSSM Higgs yet another twist

• ATLAS preliminary
• qqH, H?WW, tt
• bbH, H?tt, mm
• tbH and tH, H?tn

• CP-violation in Higgs sector
• complex couplings
• mass eigenstates H1, H2, H3 are mixtures of h, H,
  A
• production/decay modes change
• new benchmark point CPX (maximum effect)
  suggested by Carena et al., Phys.Lett B495 (2000)
  155
• new parameterization MH tanb

ATLAS L30 fb-1

• uncovered holes remain
• more studies needed

not excluded at LEP
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Summary

• Standard Model Higgs
• expect to start excluding SM Higgs at L0.1 fb-1
• discoveries may be expected already at L1 fb-1
• SM Higgs, if thats all we have, is expected to
  be discovered by the time we reach L10 fb-1
• MSSM Higgs
• nearly full (M, tanb) plane is expected to be
  covered at L30 fb-1
• there is a serious chance to see only a SM-like
  Higgs

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P.S. Lessons from Tevatron

• Life may not be as rosy as our projections are
• in 2003, the exclusion of the SM Higgs with mass
  MH115 GeV was expected to happen at L1.5 fb-1
• in 2005 and at L300 pb-1, one might expect to be
  just x2.5 away from the SM Higgs x-section
• in 2005, the limits were x50 above the SM Higgs
  x-section
• Lots of work go into Tevatron Higgs searches to
  meet the goals
• There are no reasons to believe that LHC will be
  easier

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Summary Slides
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SM Higgs
CMS 2003 CMS 2006
new
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MSSM SM-like Higgs
new
CMS 2003 CMS 2006
ATLAS
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MSSM H and A
new
CMS 2003 CMS 2006
ATLAS
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MSSM H- (old/new plots)

new
CMS 2003 CMS 2006
ATLAS