Higgs Searches at the Tevatron (Run I)

1
Higgs Searches at the Tevatron (Run I)
Lorenzo Moneta University of Geneva on behalf of
CDF and D? collaboration

• Introduction
• SM Higgs
• ZH WH with H ? bb (CDF D?)
• MSSM Higgs
• bbf with fH0,h0,A0 (CDF)
• H (CDF D?)
• Fermiophobic Higgs
• H ? gg (CDF D?)
• Conclusions

2
Introduction

• Electroweak Symmetry breaking in the SM predicts
  existence of an Higgs boson but with unspecified
  mass
• Higgs mass constraints scale ? where SM might
  break down
• if ? MPlank then 130 lt M(H) lt 180
• Current Status of Higgs searches
• SM fit to Electroweak data indicates a light
  Higgs
• M(H) lt 200 GeV _at_ 95 CL
• Direct searches from LEP2
• 95 CL limit is 113 GeV
• Indication of Higgs-like events
• in the last year data
• excess 3? at M(H) ?115 GeV

3
Tevatron (Run I)

• Tevatron
• proton-antiproton collision _at_ ?s 1.8 TeV

CDF
DØ

• Run I (Oct. 92 ? Feb. 96)
• total integrated luminosity
• 120-1 pb / detector

Expected 2 fb-1 in Run IIa !
4
SM H0 production _at_ Tevatron

• Gluon Fusion
• too difficult (QCD background)
• Higgsstrahlung
• SM cross section is very small
• 1/20 s(t-tbar)
• 1/500 s(Z/W ? 2 jets)
• possible with Run II luminosity !
• larger s with new physics ??

s 0.70 pb
for M(H) 120 Gev/c2 with QCD NLO correction
WH s 0.16 pb
ZH s 0.10 pb

• Vector Boson fusion
• radiation off heavy quark
• very small s in the SM

5
SM Higgs decays

• M(H) lt 130 GeV
• dominant decay is
• final states are for W/ZH
• need lepton ID/MET b-tags
• M(H) gt 130 GeV
• dominant decay is
• final state with ? 2 leptons
• but smaller cross-section
• interesting at RunII !

For M(H) 120 GeV/c2
6
SM H signatures (W /Z H)

• Tevatron Run I channels (W/Z H with M(H) lt
  130 GeV)
• BG QCD multijets
• BG
• BG QCD,
• BG

( 50 of W/Z H )
( 9 )
( 5.4)
( 1.8)

• Essential for these analyses
• b tagging
• good di-jet mass resolution

7
b tagging at the Tevatron

• Techniques developed for top analyses. Two
  algorithms
• Soft Lepton Tagging (SLT) (CDF DØ)
• semileptonic b decays
• DØ m ( pT gt 4 GeV) CDF m e (pT gt 2 GeV)
• Secondary Vertex Tagging (SVX) (CDF)
• reconstruct a displaced vertex in the jet
• b lifetime 1.5 ps ? decay length few mm
• use capability of Silicon vertex detectors

e(b-tag) 7/b-jet e(mistag) 0.5/jet
s(decay-length) 100 mm
b jet
e(b-tag) 20/b-jet e(mistag) 0.2/jet
secondary vertex
primary vertex
8
Search for

• Final states are lepton (e/m) MET bs
• Event selection
• high pTlepton pT(lep) gt 20 GeV hlt1
• METgt20
• 2 jets with ET(j)gt15, hlt2
• b-tags (single OR double jet tag)
• Backgrounds
• Results (CDF D?) 106 pb-1

CDF
1 b-tag
2 b-tags
mbb
from fit to di-jets mass
95 CL Limit on s?BR 26-28 pb for 90ltMHlt130
(CDF) 40-19 pb for 90ltMHlt120 (D?)
9
Search for

• Final states is MET bs
• Event selection (CDF)
• METgt40 (trigger gt35) lepton veto
• 2 or 3 jets with ET(j)gt15, ? lt2
• DF(MET,j) gt 60 for all jets (ETgt8)
• DF(j1,j2) lt 150
• b-tags (single OR double)
• Backgrounds
• QCD and
• Results (88 pb-1)

95 CL Limit on s?BR 8 pb for 90ltMHlt130
10
Search for

• Final states is di-leptons bs
• Event selection (CDF)
• pT(lep)gt20,10 GeV
• 76ltM(l,l)lt106 GeV
• 2 or 3 jets with ET(j)gt15, hlt2
• MET lt 50 GeV (against top di-lepton evts)
• 1 b-tag
• Backgrounds
• Results (106 pb-1)

mbb
95 CL Limit on s?BR 56-24 pb for 90ltMHlt130
11
Search for

• Multi-jet final state with bs
• Event selection (CDF)
• Multi-jets trigger
• ? 4 jets with SETgt125 GeV ETgt15
• double b-tag
• pT(bb)gt50 GeV
• Backgrounds
• mainly QCD (bs fakes)
• also top and Z jets
• Results (91 pb-1)

mbb
95 CL Limit on s?BR 30-16 pb for 90ltMHlt130
? Need good Mbb resolution against background
12
Combined limit for SM Higgs

• CDF combination of
• 95 CL limit on

slimit 7.4-8.2 pb for mH 90-130 GeV/c2

• x 30 SM cross-section (mH 115)
• Limit is dominated by nnbb
• Expected best limits from
• nnbb and lnbb
• poor lnbb limit due to a small excess in observed
  events
• Need more luminosity
• RUN II

LEP

SM
115
13
MSSM Higgs Search

• Two Higgs doublets in the MSSM
• 5 Higgs particles
• two neutral CP-even h0,H0
• One neutral CP odd A0
• Two charged H,H-
• two free parameters tanb and mA
• Mass relations at tree level
• m(h0) lt m(Z0) lt m(H0) m (A0) lt m(H0) m(H) lt
  m(W)
• but after radiative corrections m(h0) lt ?130 GeV
• Couplings at large tanb
• enhanced to d-type quark and leptons
• suppressed to u-type quark

14
MSSM Higgs production
tanb 3
tanb 30
h
H
h
H
s(pb)
s(pb)

• Small tanb
• SM-like cross-sections

• Large tanb
• enhanced hbb coupling
• hbb/Hbb/Abb can have large cross-sections (?
  tan2b)

In general dominant Higgss Branching Ratio are
to bb (90) and tt- (10)
15
Search for

• Exploit enhanced Yukawa couplings looking for
  bb? production (j h,HA)
• large cross sections (? tanb2)
• 4-bs jets final state
• Event selection (CDF)
• Multi-jets trigger
• 4 jets with S(ET)gt125 GeV ETgt15
• ET(j) cuts depending on m(j)
• ? 3 b-tags
• DF(bb) gt 109 (against g?bb)
• Backgrounds
• QCD (bb/cc), Z/Wjj, top

CDF results (91 pb-1)


16
Limit for
s?BR lt 25.7 pb

• Limit (95CL for Mj 100 GeV)
• convert s?BR limit in tanb vs Higgs mass
  exclusion
• No mixing Maximal Mixing for the stop

tanb vs m(h)
tanb vs m(A)
Tevatron complements LEP !
17
Charged Higgs Searches

• Searches for t? Hb when M(H) lt mt - mb
• decay t? Hb can compete with SM decay t? Wb
• BR(t? Hb) depends on tanb

• Direct Search (CDF)
• look for H ? tn in t-tbar evts
• BR(H ? tn) 1 for large tanb
• WHbb or HHbb channels in addition to WWbb
• look for l t MET jj events (l e,m,t)
• use t identifications via hadronic decays
  (tracking calorimeter)
• backgrounds
• Z ? tt jj, W?3 jets, WW/WZ
• acceptances for single and double H? production

18
Charged Higgs Searches

• Indirect Search (CDF D?)
• look for lepton disappearance in t-tbar events

• suppression of dileptons and lepton jets events
  
• rate of the two depends on BR(t ? Hb)
• t-tbar cross-section independent of m(H), tanb
• given measured x-section (when BR(t ? Hb) 0)
• exclusion regions in the
• m(H)-tanb plane

D0
LEP2 (ADLO)
New Exclusion regions at low and high tanb
19
Fermiophobic Higgs

• In some models Higgs couples only to vector
  bosons
• BR(H ? gg) dominant for light Higgs (m(H) lt 100)
• Searches for W/Z H ? ggjj
• D? search
• di-photons jets
• Backgrounds from QCD
• fakes or real g in jets
• CDF search
• di-photons with e/m MET or jj
• Limit For SM cross-section
• M(H) gt 80 GeV (95 CL)
• LEP limit is 105 GeV

D0
20
Conclusions

• SM Higgs searches are luminosity limited in Run I
  
• no sensitivity to SM cross sections
• no excess seen and set limits at 30 SM
  cross-section
• provided experience for Run II
• developed techniques for low mass Higgs searches
• b tagging and di-jet mass resolution are crucial
  !
• good expectations for Run II
• see next talk on Run II prospects
• Nice exclusion results for MSSM Higgs
• bbj search with sensitivity for high tanb region
• charged Higgs from t ? Hb
• probed regions inaccessible to LEP
• very interesting in Run II

report of the Tevatron Higgs Working Group
(hep-ph/0010338)