Higgs Searches at the Tevatron: Run I

1
Higgs Searches at the Tevatron Run I
Jacobo Konigsberg / Univ. of Florida / CDF

• Introduction
• The Higgs
• Run I
• SM Higgs (CDF/D0)
• ZHo WHo
• MSSM Higgs
• bbj jHo,ho,Ao (CDF)
• H (CDF/D0)
• More beyond
• Bosophilic (CDF/D0)
• Conclusions

2
The Hoiggs why? where?

• an EWSB mechanism in SM
• Gives mass to particles through H couplings
• H mass unspecified in SM but couplings are
  specified
• Mtop, MW and MHiggs related via higher order
  loops
• Current data points to light Higgs
• MHiggs lt 170 GeV _at_ 95, Osaka00
• Higgs-like events observed at LEP2 before
  shutdown
• 114 GeV 95 CL exclusion limit
• The Higgs mass constraints the scale where the SM
  might break down (?)
• 130ltMHlt180 GeV/c2 ? ? Mplank
• Possible to discover at Tevatron in the next few
  years weve started

3
Run I

• 4 mile circ. superconducting ring
• 6x6 proton anti-proton bunches
• 3.5 us / crossing
• 1.8 TeV cm energy
• 1030-1031 inst.luminosity

Run I tot. integrated luminosity 120-1
pb/detector
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Physics processes _at_ Tevatron
Looks interesting
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SM Higgs production _at_ Tevatron

• Dominant processes _at_?s2TeV

Gluon fusion
Higgsstrahlung
Vector boson fusion
Larger x-sect with new physics?
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SM Hoiggs decays
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SM Hoiggs signatures
b-tagging and Mbb resolution are critical for a
ligth Higgs
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Tevatron Run I Detectors
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B-tagging in Run I

• Displaced vertices t(b)1.5 ps ? Lxy(b)
  O(mm)

CDF
Silicon Vertex Detector (SVX)
1 vertex lt 2 tracks Lxy/sLxy gt 3.0 sLxy
100µ
e(b-tag) 25/b-jet (4 c-jet)
e(b-tag) 45/event w/ 2bs
e(b-tag) 0.2/jet

• Semileptonic b decays

CDF/D0
e(b-tag) 7/b-jet
e(b-tag) 16/event w/ 2bs
e(b-tag) 0.5/jet
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Run I Mass Resolution
Specific b-jet corrections
Can see
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CDF
Backgrounds Wbb, tt, WZ, tb

• Event selection
• High Pt central
• Pt(lep)gt20 GeV, Metgt20, Pt(j)gt15, etalt2
• b-tags

D0
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Backgrounds QCD, tt, Zjj, W/Zbb

• Event selection
• Multi-jet trigger sum(Et)gt125 GeV 4-jets
• 2 b-tags
• Pt(b,b)gt 50 GeV
• Need good M(bb) mass resolution

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Backgrounds QCD, Zbb, ZZ, tt, tb

• Event selection
• Met gt 40 GeV
• Veto isolated leptons/tracks
• Et(j) gt 15 GeV (2 or 3)
• Df(Met,j) gt 1.0
• Df (j1,j2) lt 150o
• b-tags

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Backgrounds Zbb, ZZ, tt, tb

• Event selection
• Pt(lep) gt 420 GeV
• 76ltM(l,l)lt106 GeV
• Pt(j) gt 15 GeV, etalt2
• Met lt 50 GeV (veto top)
• 1 b-tag

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Run I Higgs Limits
D0
cdf

• SM Higgs limits
• Production x Branching Ratio
• 95 CL about 30 times higher than SM prediction
  (for MH115 GeV)
• Sets the scale for needed Luminosity, si?
• Best limit from HZ?bbnn channel but due to
  observed data
• Expected best channels are HZ?bbnn and HW?bbln

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CDF tagged events
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MSSM Higgs Searches

• In the MSSM scenario
• Two Higgs doublets lead to 5 Higgs particles
• Two neutral CP-even ho,Ho
• One neutral CP-odd Ao
• Two charged H ,H-
• Masses governed by two parameters, for ex
• Tree level mass relations
• M(ho)ltM(Zo)ltM(Ho)
• M(Ao) ltM(Ho)
• M(H)ltM(W)
• But M(ho)lt130 GeV after radiative corrections
  (top,stop etc.)

130 GeV
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MSSM Higgs production _at_ Tevatron

• H/h/A can have SM-like x-sections at small tan b
• For processes such as HW and HZ

• Some production processes such as
• Hbb/Hbb/Abb
• can have
• large x-sections at large tan b !!!

g 1/cos(b) tan(b)
? h,H,A
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MSSM Higgs Branching Ratios
A
H
h
?
tan b 5
For all practical purposes ??bb 90 ??tt
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tan b 50
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? h,H,A

• Event selection
• 4- jets ?ETgt125 GeV trigger
• ET cuts on jets m? dependent
• ? 3 b-tag (secvtx)
• ??bb gt 1.9

mh
Backgrounds QCD, Z/Wjets,tt
mA
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Charged Higgs Searches

• If then competes with
  
• Depending on tanb

Search directly via
Using hadronic tau identification
trackingcalorimeter Look in e,mu tau and in
taujetsMet channels

• Search indirectly via lepton disappearance in
  t-tbar events
• Dilepton leptonjet top events suppressed
• Given t-tbar x-sect mH,tanb how likely is it
  to have observed N events?
• ? exclusion regions in mH,tanb

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Charged Higgs Results
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Bosophilic/Fermiophobic Higgs

• Some models with two (or more) Higgs doublets
  predict Ho couplings only to vector bosons, with
  H?gg to be dominant for low mass Higgs.

Backgrounds Mostly QCD
D0

• Event selection
• Isolated, high-Pt, central, photons
• High-Pt jets/leptons/MET

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Bosophilic Higgs Limits
D0
CDF
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Conclusions

• Run I
• Searches in all channels for MH lt 130 GeV/c2
• No sensitivity to SM Higgs, but we looked anyway
• No sign of new physics
• Combine results to set limits on ?xBR
• Detectors, backgrounds, taggers understood !
• Good experience and baseline for Run II
• Sensitivity to neutral MSSM Higgs sector for
  large tan?
• Excluded MSSM regions
• Run II
• Many, many, improvements
• We have a chance! (see next talk)