Moriond%20ElectroWeak%202005,

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Results on Higgs Searches _at_Tevatron

• Moriond ElectroWeak 2005,
• Gregorio Bernardi, Paris/FNAL,
• for the CDF and DØ Collaborations

Tevatron/ Luminosity CDF and DØ SM Higgs
Searches b-tagging / Z?bb BSM Higgs
Searches Summary Only Results new since last
Moriond are shown, i.e no unstable H, nor H? ??
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Tevatron Parameters
Upgrades for Run II 2001-2009 ?10 energy
increase 30 higher stop ?integrated
luminosity increase x50 Plan (build higher
antiproton stacks!) - Increase of protons on
antiproton target - Optimization of transfers,
improved optics/helices - Increase p
stacking/storing (mixed mode/e-cool) - Upgrade
Tevatron for higher bunch intensities
Since last Moriond improvement in reliability /
operating efficiency ? in stores 120
hours/week Typical ratio of recorded to
delivered luminosity is 80-90 So far both
exper. recorded 0.8 fb-1 Results presented on
0.2-0.3 fb-1
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Tevatron Run II Performance
1.1032 cm-2sec-1
0.8 fb-1
Peak luminosity is above 1.1032 cm-2sec-1
Total 0.7 fb-1 delivered in Run II
2004 above Design !
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Tevatron Long Term Luminosity Plan
Currently expecting delivered luminosity to each
experiment ? 4 - 8 fb-1 by the end of 2009
Increase in number of antiprotons ? key for
higher luminosity Expected peak luminosity ?
3.1032 cm-2sec-1 by 2007
Today
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The DØ Experiment in Run II
LAr/U Calorimeter, fine-grained, hermetic New
trackers ? Silicon microVTX,
? Central Tracker (Scint Fibers) 2T
superconducting solenoid Pre-shower
detectors Upgraded muon detectors Faster readout
electronics New trigger DAQ
Total of 800,000 Silicon channels
55000 Calorimeter cells
80,000 channels in the Central Fiber Tracker
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SM Higgs Production and Decays
Production
Decays
Production cross section ? in the 1.0-0.1 pb
range for gg ? H ? in the 0.2-0.02 pb range for
associated vector boson production
Dominant Decays ? bb for MH lt 135 GeV ? WW
for MH gt 135 GeV
Search strategy MH lt135 GeV associated
production WH and ZH with H?bb decay Backgrounds
top, Wbb, Zbb MH gt135 GeV gg ?H production
with decay to WW Backgrounds electroweak WW
production
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Experimental Limits on Higgs Mass

• direct searches at LEP
• MH gt114 GeV at 95 C.L.
• precision EW fits (winter 2005)
• MH 12673-48 GeV
• MH ? 280 GeV _at_ 95 C.L.
• ? Light Higgs favored

LEP
Tevatron provides Precision measurements of
mtop Mw and Direct searches ? SM Higgs ?
non-SM Higgs
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Tevatron SM Higgs Search Outlook
LEP
Ldt (fb-1)
Updated in 2003 in the low Higgs mass region
W(Z)H?ln(nn,ll)bb to include ? better detector
understanding ? optimization of analysis
Tevatron
Sensitivity in the mass region above LEP limit
starts at 2 fb-1 Meanwhile ? optimizing
analysis techniques ? understanding detectors
better ? searching for non-SM Higgs with higher
production cross sections or enhanced
branching into modes with lower backgrounds
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SM Heavy Higgs H ? WW ? lnln
Search strategy ? 2 high Pt leptons and
missing Et ? WW comes from spin 0
Higgs leptons prefer to point in the same
direction
H
Main Background WW Production
Good agreement with NLO theory 12.0-13.5 pb
Now Measured at the Tevatron by both Experiments
Ohnemus, Campbell, R.K.Ellis
DØ PRL/ hep-ex/0410062
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Search for H ? WW
Search in 3 channels H?WW?ll??
with l ee,??,e? ?inclusive
high pT lepton triggers integrated luminosity
184 pb-1 (CDF), 147-177 pb-1(D0)
95 CL for the 3 channels sBR(H?WW) lt 5.7pb
For MH160 GeV
D? Obs 9 evts Bkgnd11.1 ? 3.2 Signal 0.27 ?
0.004 (mH160 GeV)
CDF Obs 8 evts Bkgnd 8.9 ? 1 Signal 0.17 ?
0.02 (mH180 GeV)
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Search for WH ? WWW
Search of high-pT isolated like-sign (LS)
dilepton events in 193.5 pb-1 data. leading
lepton pT,1 gt 20 GeV, 2nd lepton pT2 gt 16 GeV,
pT12vect.sum of 1,2 gt 35 GeV. Search in the
(pT,2,pT,12) plane - 0 events found -
total exp. Backgnd 0.95 - 0.61(stat) -
0.18(syst) - bosophilic Higgs (110 GeV) exp. to
be about 0.06 evts . (assuming same
production x-section as SM Higgs) - SM Higgs
(160 GeV) expected to be about 0.03 evts.
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Low Mass (lt135 GeV) Higgs Search

• Also difficult at LHC (combination of several
  channels)
• At Tevatron need to fully exploit associated
  productions
• WH and Z (?ll- or ??) H with H ? bb ??
  b-tagging
• Understand intrumental and SM backgrounds
• ?W,Zheavy flavor are backgrounds to leptonic
  WH,ZH
• instrumental background (QCD) is difficult for ??
  H
• Here after, results for b-tagging, Z and W
  Heavy Flavor,
• WH, and SM Higgs prospects

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Tagging b-quarks (B-hadrons)

• Top, Higgs have b-quark jets
• Leptons from B meson
• Contain a B meson
• Has finite life time
• Travels some distance from the vertex before
  decaying
• 1mm
• With charm cascade decay, about 4.2 charged tracks

Vertex Tagging a B (transverse plane)
B
(Signed) Track
Impact Parameter (dca)
Decay Lengh (Lxy)
Hard Scatter
Several algorithms under development/improvement
3 main categories - Soft-lepton tagging - Impact
Parameter based - Secondary Vertex reconstruction
Impact Parameter Resolution
dca/s(dca)
Decay Length Resolution
Lxy/s(Lxy)
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Impact Parameter (dca) Algorithms
Jet Lifetime Impact Parameter
Based on signed dca Significance.
Light jets same flat probability for postive
negative dca significance
Probability distributions P(Track from
PV) Defined for each class of tracks of SMT
Hits, pT, etc.
To each jet is assigned a Probability to be a
light quark Pjet
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b jets probability for positive dca sign.
peaks at 0.
0.5
Light Quark Fake Rate
Another algo also used in D0 counting displaced
tracks
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SVT Algorithm
Secondary Vertex Tagger
Reconstruct Vertices using displaced tracks
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Cut on Decay Length Significance
S(Lxy) Lxy/s(Lxy).
0.5
Performance on signal
tt leptonjets 56 Single Top (s channel)
52 Wbb 52 Wj 0.3
Z axis
Combining the 3 Taggers, correlations already
studied
N.B. in D0, b-tagging efficiency is defined
w.r.t. taggable jets, i.e. results are slightly
higher than if estimated w.r.t to all jets
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Secondary Vertex Algorithm
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Performance on signal
SecVtx tagger efficiency to tag jets in top quark
MC samples, as obtained by multiplying the tag
rate for such MC jets by the data/MC scale
factors 0.9090.060 for the tight tagger and
0.9270.066 for the loose tagger. The bands
represent the systematic error on the data/MC
scale factors.
0.5
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3 views of a high dijet mass (220 GeV) Wbb (WH)
candidate
ETmiss
Vertex view of a low mass candidate
Clean Events! Mass Reconstruction?
ETmiss
b-tags
dijet mass (48 GeV)
electron
ETmiss
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First steps in Measuring Z? bb
Dijet invariant mass of 85,794 events with both
jet containing a secondary vertex b-tag. Events
are selected from 333 pb-1 of CDF data (dedicated
trigger). Two leading jets must be back-to-back
in azimuth (Delta Phigt3.0), and the event must
have no other jet with ET above 10 GeV. The
background shape is computed using untagged data
passing the same selection. The Z-gtbb signal
shape is computed with Pythia The 2 shapes are
fit to the experimental data (blue points) Fit
results are in red Fit uncertainties are stat.
only.
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Z Heavy Flavor Production

• Zheavy flavor is background to ZH
• Z single b-tag
• Probe of b-quark PDF
• b PDF is important for hb and single-top
  production

• Measure s(Zb)/s(Zj)
• Many systematics cancel
• Selection
• Z in ee and mm channels (cut on mass window)
• ?1 Jet pTgt20 GeV, ?lt2.5
• 3458 Zjet events

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s(Zb)/s(Zj)

• Disentangle light, c, b contributions
• Use light and b-tagging efficiency from data
• c-tagging efficiency from MC and scaled for
  data/MC difference in b-tagging
• Nc1.69Nb from theory
• Cross checks with
• Soft lepton tagging
• Impact parameter tagging
• 0.024?0.005(stat)?0.005(syst)
• Theory predicts 0.018
• Large part of systematic error from tagging
  efficiency and background estimation

• Apply sec. vertex b-tag
• 42 events with ?1 tag
• 8.3 from QCD background (sideband)

signal
Sec. Vtx displacement/resolution
Submitted to PRL - hep-ex/0410078
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174pb-1 sample with one electron and
(dominant backgd for WH)
Compared to ALPGEN, PYTHIA showering, and full
detector simulation. Normalized to NLO x-section
(MCFM for Wjets)
Electron pT gt 20 GeV, ?lt1.1 Missing ET gt 25
GeV 2 Jets pT gt 20 GeV/c, ?lt2.5
?2540 evts (2580 ? 630 expected)
? ?1 tag 76 evts (72.6 ? 20 exp.)
Data well described by simulation
Total experimentalsyst. Error 15
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95 CL upper limit on WH production of 9.0 - 12.2
pb for Higgs masses of 105-135 GeV Published Run
II limit better than Run I ? detector improvements
6 evts (4.4 ? 1.17 expected)
95 CL upper limit of 6.6 pb on
production for b with pTb gt 20 GeV and
gt0.75
Accepted in PRL - hep-ex/0410062
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162pb-1 sample with one electron or muon and

Electron or muon pT gt 20 GeV/c Missing ET gt 20
GeV 2 Jets pT gt 15 GeV/c, ?lt2.0
Total systematic error 11 No significant peak
from Higgs
W 1b-tagged jet
W2 jet events (before b-tagging)
Data well described by simulation
62 evts (66.5 ? 9 expected)
2540 evts observed
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Wbb ? WH SM Higgs Prospects
Future improvements Extend b-tagging acceptance,
efficiency Additional kinematic
variables Better Mbb resolution Add ??bb channel
95 CL upper limit on
5.3 (4) pb _at_
mH115 (150) GeV
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• Search for neutral Higgs in a two-Higgs-doublet
  MSSM SUSY model.
• 260 pb-1 sample of triple b-tagged multi-jet
  events.
• No distinction between h or H and A

SUSY-MSSM
h
h
Sample Selection - Trigger gt3 jets with
ETgt15 GeV, - Offline cut on ET of leading jets
optimised for each Higgs mass. - 3
b-tagged jets or more Background QCD heavy
flavor bbjj, ccjj, cccc, bbcc, bbbb QCD
fakes jjjj Other Z(bb,cc), tt
Theory/Simulation
NLO SM Higgs production
(Campbell et. al., Dawson et. Al), MSSM
(Carena, Mrenna, Wagner), PYTHIA,
MADGRAPH, ALPGEN
Di-jet mass in ? 3b-tagged events
260 pb-1
No excess of events observed
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Limits on signal production cross section in
the tan ß vs. mA plane
260 pb-1
Two benchmark MSSM scenarios
260 pb-1
? lt 70-20 pb for mA90-150 GeV
Exclude significant portion of tan ß down to 50,
depending on mA and MSSM scenario
For mA120 GeV ? lt 31 pb-1 _at_ 95c.l., tan? lt 55
_at_ 95c.l. (Max Mixing)
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Search for gg ?h ? tt-
200 pb-1 sample from t triggers (leptonisolated
track) two ts, one decaying into hadronsn and
the other to an e/m 2n.
Cuts on lepton pT, Z mass window. To remove
light quark bkgnd
PYTHIA Tauola (signal simul.)
230 evts. obs. 263.6?30.1 exp.
Limit on sxBR extracted from likelihood fit of
the partial mass distribution
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Search for H/H--
Predicted by some beyond SM models like
Left-Right Symmetric Models If short lived ?
prominent signature multiple high Pt leptons,
like sign di-lepton mass peak ? backgrounds WZ,
Wjets, conversions (e) If long lived (ct gt 3
m) ? two high ionization tracks
D0 (113 pb-1) M(HL) gt 118 GeV (mm) at 95
C.L. CDF (240 pb-1) M(HL) gt 136 GeV (mm) at 95
C.L.
Background lt 10-5
MHgt134GeV
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Summary
No deviations from SM observed (yet)
Higgs search is in progress ? SM Higgs
? sensitivity (mH gt114 GeV) starts at 2 fb-1
(Moriond 07 ?) ? non-SM Higgs ? many
different models tested ? already see
reduction in allowed phase space (Run I, LEP)
Expect substantial improvements in Higgs hunting
with 0.8 fb-1 already on tapes 8 fb-1 expected
in Run II
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Backup
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Data Collection by the Experiments
Typical ratio of recorded to
delivered luminosity is 80-90 As of now both
exper. recorded 0.7 fb-1 Results presented
correspond to 0.3 fb-1
Analyzed data
Analyzed data
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Search for H ? gg

• In the SM Higgs ? gg has Br10-3
• ? search for SM Higgs decaying to gamma
  pair is not practical at Tevatron
• Many SM extensions allow enhanced gamma pair
  decay rate largely due to suppressed coupling to
  fermions
• ? Fermiphobic Higgs
• Topcolor Higgs
• Search strategy
• Look for peaks in gg mass spectrum for high Pt
  isolated gs

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D? rules out the m(?T)200 GeV m(??T)105 GeV
combination for MV between 200 and 500 GeV
CDF ? x-section limits for m(??T0) between 85
and 120 GeV