Post on 30-Jan-2016
description
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 1
Higgs Searches atTevatronStéphanie Beauceron
LPNHE - Paris
on behalf of CDF and DØ Collaborations
CDF
Thanks to everybody for their contribution to this talk
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 2
• Standard Model Higgs• Higgs Beyond the
Standard Model• limits on Wbb/WH
production (Z+b)/(Z+j) ratio• limits on HWW(*)l+l-
production• limits on neutral Higgs at
high tanβ• limits on Non-SM h
production• limits on H++/H--
• Summary
Main Injector & Recycler
Tevatron
Chicago
p source
Booster
p
p
p p
1.96 TeV
CDFDØ
36×36 bunches396 ns bunch crossing
Outline
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 3
36×36 bunches396 ns bunch crossing
design: challengingbase: conservative
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11/23/03 12/21/03 1/18/04 2/15/04 3/14/04
Inte
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-1)
Meas
Design
Base
FY’04 Integrated Luminosity
11/23/03 1/18/04 3/14/04
Measured luminosity
12 pb-1 / week is also above the design projection
Start of Fiscal Year
Inte
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Lu
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fb-1)
Tevatron: current and projected performance
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 4
Standard Model Higgs
• Production cross sections are small 0.1 - 1 pb depending on MH
• MH 135 GeV
gg H bb dominated by QCD background
searches can be performed in W/Z associated production to handle backgrounds
• MH >135 GeV
gg H WW(*)l+l- final states can be explored at higher masses
H bb
H WW(*)
Dominant decay modes
Production Cross section
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 5
New EW constraintConstraint mH in the Standard Model
Direct searches at LEP2: mH>114.4 GeV @95%CL
Old Top mass combination
New Top mass combination using new DØ run I measurement
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Higgs Beyond the Standard Model•MSSM
–5 physical Higgs:•Two CP-even scalars: h (lighter, SM-
like), H (heavier)•CP-odd scalar: A •Charged Higgs pair: H±
–At tree-level, two free parameters•Ratio of vacuum expectation
values:
•One higgs mass
•Other Possibilities–Left-Right Symmetric, Little Higgs,
Higgs Triplet models: Doubly Charged Higgs–SM extensions that suppress fermion
couplings •Fermiophobic Higgs•TopColor Higgs
d
u
v
vtan
222WAHmmm
Large enhancement of rates over HSMbb
MSSM Higgs Main Decay
h/H/Abb ~ 90%h/H/A ~ 10%H+ ~ 100%
(tan>1)
MSSM Higgs Production Cross section
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DØ in Run II is able to b-tag up to |η| < 2.5
Performance being improved
b-jet tagging• Essential for Hbb searches
• Can make use of the track impact parameter (IP) measurements or secondary vertex reconstruction
• CDF: performance of sec. vtx. algorithm (after kinematics cuts)
– ~50% b-tag efficiency for ~0.6% light quark mis-tag rate in |η| < 1
Both experiments are demonstrating good b-tagging capabilities
DØ RunII Preliminary
b-tagging efficiency vs light quark mis-tag rate
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DØ: W(e)bb production (1)• Motivation:
– Background to WH production• Event selection
– Central isolated e, pT > 20 GeV– Missing ET > 25 GeV– ≥ two jets: ET > 20 GeV, |η| < 2.5
• 2587 evts. in Lint=174 pb-1 of data
Good understanding of data
• Simulations with Alpgen plus Pythia through detailed detector response
• Cross sections normalized to MCFM NLO calculations
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DØ: W(e)bb production (2)
• Observe 8, expect 8.3±2.2• Bkgd. dominated by top evts.
Require jets to be tagged, consistent result with different b-tagging algorithms
Good agreement between data and MC in
both cases
One b-tag
At least two b-tags
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DØ: W(e)bb production (3)
• W Transverse mass of 2 Tagged events, keep event with 25 GeV<MT(W)<125 GeV
We observed 5 events, expect 6.9 1.8 eventsSet limits on production of (Wbb) < 20.3 pb at 95% C.L.
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 11
DØ: W(e)bb production (4)
• Optimize Wbb signal by suppressing the top production by requiring exactly two jets
Observe 2 evts., expect 2.5±0.5
Wbb Wc(c) Wjj tt+t Others
1.4±0.4
0.3±0.10.1±0.0
30.6±0.
20.1±0.0
3
• Sample composition
Probability(B)=0.04 ; Probability(S+B)=0.23
Standard Model without Wbb disfavored at 2 level
•Requiring all jets to be b-tag by the 3 b-tagging algorithms of DØ to reduce the background
Observe 2 evts., expect 0.3±0.1 (Bckd) + 0.6±0.2 Wbb (Signal)
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Vertex view of 2nd candidate
3 views of high dijet mass (220 GeV) Wbb (WH) candidate
dijet mass (48 GeV)
ETmiss
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DØ: W(e) H(bb) production
Observe 2 evts., expect 2.5±0.5
In Mass windows [85-135] we observe: 0 events0.54 ± 0.14 expect background0.03 ± 0.01 WH
Systematics studies:
Source Uncertainty(%)
Jet energy scale
14
Jet ID 7
b-tagging 11
Trigger & e ID 5
EM scale 5
MC simulations
15
Total 26Set limits on production of (WH)B(Hbb) < 12.4 pb for MH = 115 GeV at 95%
C.L.
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CDF: W(e/)H(bb) production (1)
•Event selection
–Central isolated e/, pT > 20 GeV
–Missing ET > 20 GeV
–Two jets: ET > 15 GeV, || < 2
–Veto•Di-lepton, extra jet
Observe 2072 events in data in Lint=162 pb-1
•Simulations performed with Alpgen plus Herwig passed through detailed detector response
Good agreement betweendata and MC
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CDF: W(e/)H(bb) production (2)
•Enrich the b-content of events–Require at least one b-tagged jet
Observe 62 events in data Expect 61 ± 5 events
•Main contributions to the bkgd:
•Expect 0.3 evts from Higgs–Signal acceptance of ~ 1.8% for
MH = 110 – 130 GeV
good agreement betweendata and MC
Mistags
Wc(c) Wbb QCD top
14 13 12 10 9
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CDF: W(e/)H(bb) production (3)
Set limits on the Higgs production cross section times branching fraction at 95% C.L. :
×B < 5 pb
Systematics studies
Exceeds CDF’s Run I limit [PRL 79, 3819(1997)]
×B < 14 – 19 pb for MH = 70 – 120 GeV
Source Uncertainty (%)
ISR / FSR 19
Secondary vertex
8.6
Lepton ID 5
Jet energy scale
3
PDF 1
Trigger 0.7
Total 22
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• Motivation– Background to ZH
production– Probes PDF of the b-quark
• LO diagrams for ZQ
• Measure cross section ratio (Z+b)/(Z+j) Many uncertainties cancel
DØ: Z(ee/)b production (1)• Data correspond to integrated
lumi. of 184 (ee), 152 () pb-1
• Event selection– Isolated e with pT > 15/20
GeV, || < 2.5/2.0– Z peak for signal, side bands
for bkgd. evaluations– Jet ET > 20 GeV, || < 2.5– At least one b-tagged jet
• Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response
• Cross sections normalized to data
• Relative b- and c-quark content as given by MCFM NLO calculations
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DØ: Z(ee/)b production (2)
• Transverse energy spectrum of b-tagged jets
– QCD and mistag bkgd. estimated from data
– MC: Pythia Zb normalized to data
• Measure cross section ratio Z+b/Z+j 0.024 ± 0.005 (stat)
(syst)
Theory: ~0.02 hep-ph/0312024
• Systematics studiesSource Uncertainty (%)
Jet tagging 16
Jet energy scale
11
Bkgd. estimation
6
(Z+c)/(Z+b)
3
Total 20
+ 0.005– 0.004
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DØ: H WW(*) l+l- final states; l=e,
•Event selection–Isolated e/
•pT(e1) > 12 GeV, pT(e2) > 8 GeV•pT(e/1) > 12 GeV, pT(e/2) > 8 GeV
•pT(1) > 20 GeV, pT(2) > 10 GeV–Missing ET greater than
•20 GeV (ee, e); 30 GeV ()–Veto on
•Z resonance•Energetic jets
•Simulations done with Pythia passed through detailed detector response
–Rates normalized to NLO cross section values
•Data correspond to integrated lumi. of~ 180 (ee), 160 (e) and 150 () pb-1
Data vs MC afterevt. preselection
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• Higgs mass reconstruction not possible due to two neutrinos
• Employ spin correlations to suppress the bkgd.
(ll) variable is particularly useful
• Leptons from Higgs tend to be collinear
DØ: H WW(*) l+l- final states; l=e,
W+ e+
W- e-
Azimuthal angle between e and (after event pre-selection)
Higgs of 160 GeV
Good agreement between data and MC in all
final states, and all variables examined so far
DIS 04 Stephanie Beauceron - LPNHE Paris VI et VII 21
• Number of events after selections
• Dominant bkgd. in e sample
DØ: H WW(*) l+l- final states; l=e,
Signal acceptance is ~ 0.02 – 0.2 depending on the Higgs mass/final state
WW W+jets WZ tt
2.51±0.05
0.34±0.02
0.11±0.01
0.13±0.01
ee e
Observed 2 2 5
Expected 2.7±0.4
3.1±0.3 5.3±0.6 Excluded cross section times
Branching Ratio at 95% C.L.
DØ Run II Preliminary
Higgs of 160 GeV
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bbbbbbqqgg , (=h,H,A)
•Event Selection:– Multi-jet data sample – At least 3 jets:
ET cuts on jets are optimized separately for different Higgs mass points, and for min. # jets required in the event
3 b-tagged jets– Look for signal in the invariant
mass spectrum from the two leading b-tagged jets
•Simulations performed with Pythia or Alpgen plus Pythia passed through detailed detector response
•Data correspond to integrated lumi. of 131pb-1
BR( ) ~ 90%bb
(Higgs signal at 95% C.L. exclusion limit)
DØ: Neutral Higgs Bosons at High Tan in Multi-jets Events
Dijet Mass
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DØ: Neutral Higgs Bosons at High Tan in Multi-jets Events
Signal acceptance is ~ 0.2 – 1.5% depending on the Higgs mass/final state
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•Some extensions of SM contain Higgs w/ large B(H)
–Fermiophobic Higgs : does not couple to fermions–Topcolor Higgs : couple to top (only non-zero fermion coupling)
•Data correspond to integrated lumi. of 191 pb-1
•Event selection– 2 Isolated with pT > 25 GeV, ||<1.05 (CC) or 1.5<||<2.4 (EC)
– pT > 35 GeV
•Dominant uncertainty in background estimation is in the measurement of mis-ID rate (~30%)
DØ: Search for Non-SM Light Higgs in H
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•No clear evidence of excess
•Perform counting experiments on optimized sliding mass window to set limit on B(H) as function of M(H)
DØ: Search for Non-SM Light Higgs in H
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•H++/H-- predicted in models that contain Higgs triplets
•Left-Right (LR) symmetric models•SUSY LR models : low mass (~100 GeV – 1 TeV)
•Event selection– 1 pair of same sign ee, or , or e in mass window of 10%*M(H++) (~3 detector resolution)
•same sign leptons decay contains low SM backgrounds, provide clean environment for new physics search
•Data correspond to integrated lumi. of 240 pb-1
CDF: Search for H++
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Decay Channels
# predicted Evts
ee
e
8.06.08.1
6.05.08.0
4.04.09.0
•Background prediction for M(l+ l+) >80 GeV (>100 GeV for ee)
•Data : observe 0 event
Mass Limit
CDF 240 pb-1
D 106 pb-1
HL++ HR
++ HL++ HR
++
ee 135 ~102-113
135 113 116 95
e 115
CDF: Search for H++
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Prospectives for Higgs• New study from CDF + DØ :
Improvement of the results with a detailed simulation.
5 discovery
3 evidence
95% CL exclusion
Statistical power onlySystematics not included
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Summary• Hunting for Higgs at the Tevatron Run II has begun !• Understanding of the background processes to the Higgs production is
gradually improving• Result summary:
(Wbb)< 20 pb (WH) B(Hbb) < 12 pb (We) (WH) B(Hbb) < 5 pb (We and W) (Z+b)/ (Z+j) = 0.024 ± 0.005 (stat) (syst)– limits set on (H)B(HWW(*))– Search for Neutral Higgs in MSSM:
• excludes A and h/H for masses 90-150 GeV/c2 at high tan β (>~100)
– H++ Search: • Limits 115, 135, 135 GeV/c2 for exclusive HL
decays to e, ee, • Limits 110 GeV/c2 for exclusive HR
decays to – Search for H:
• Limits are set for the Branching Ratio vs Mass for both Fermiophobic and TopColor models
Already a lot of results and more are coming!
+ 0.005– 0.004
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The upgraded CDF and DØ detectors
• Newsilicon detectordrift chamberTOF PID system
• Upgradedcalorimeter, muon systemDAQ/triggerdisplaced-vertex trigger
• New (tracking in B-field)silicon detectorfiber tracker
• Upgradedcalorimeter, muon systemDAQ/trigger(displaced-vertex trigger soon)
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Run I CDF H+ Search
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DØ H++ Search (1)•search assume the H±± decay branching ratio to like-sign muons to be 100%.
•Muon ID and analysis requirements•Make data quality requirements based on official good run lists •Select di-muon trigger events
•Have muon identification requirements based on:
– Track segments reconstructed in the muon system, isolation from signficant energy deposition in the calorimeter and an associated track from the central tracking system. The muon momentum is taken as the central track momentum
•Muons are required to have pT > 15 GeV and |eta| < 2
Dimuon mass spectra at various steps of the event selection procedure
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DØ H++ Search (2)•Search assumes the H±± decay branching ratio to like-sign muons to be 100%. •Confidence level of the signal as a function of the H++ mass,for the left- and right-handed Higgs bosons