Gregorio Bernardi, LPNHEParis VI

1
Status of Higgs Searches _at_ DØ

• Gregorio Bernardi, LPNHE-Paris VI VII

Publications Publications to come, p17 prel. SM
Higgs Searches at High mass Combined D0 and
CDFD0 results. Susy Higgs status Future plans
2
Publications

• 03 1 H
• 04 2 WH, Zb/Zj (and WW
  x-section)
• 05 2 bbh , H? WW
• 06 4 so far (based on 260-350 pb-1
  of data)
• h ? t t- (includes combination
  with hbb)
• WH ? WWW
• ZH ? n n b b
• Z n jets x-section

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P14 Publications coming
SM WH (e, m)
(moriond) ZH ? l l- b b (ee, mm)
(ICHEP) SM combination
(ICHEP) Z ? bb (x-section)
(ICHEP) SUSY bbh with h
? t t- (ICHEP) Technicolor e
and m channels (ICHEP)
4
P17 Preliminary Results
SM Zjets Sherpa study (moriond)
H? WW (ee, em) (moriond)
(mm)
(ICHEP) Updated SM combination
( CDF) SUSY bbh with h?bb
(ICHEP) In the works (cf Higgs p17 meeting
tue/fri.) ZH ? nn b b, ZH ?
l l- b b (ee, mm) WH (e, m)
h? t t H (direct,
indirect)
5
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. But Higgs mass peak cannot be
reconstructed due to the presence of 2 n? look
for an excess CDF and DØ already published on
0.3-0.4 fb-1
H
4th generation?
Updated DØ analysis L 950 pb-1 in H ? WW ? ee
and em
L 930 pb-1 in H ? WW ? mm

• Selection
• Presection lepton
  ID, trigger, opposite charge leptons
• Remove QCD and Z?ll- ET gt 20 GeV
• Higgs Mass Dependent Cuts Invariant Mass
  (Mll-) Min. Transverse Mass
  Sum of lepton pTl and ET (S pTl ET)
• Anti tt(bar) cut HT S
  PTjet lt 100 GeV
• Spin correlation in WW pair Df(l,l) lt 2.0

Major backgrounds WW production , W jet/g
production
6
H?WW final selection
mm
em
ee
selections
MH160GeV (x10)
7
Results for H?WW
If mH 160 GeV, ? 2 higgs in our sample!
SM only a factor 4 away We exclude 4th
generation models, for which mH150-185
GeV
8
Search for WH?WWW (2 like-sign leptons)
Low BR, but channel important in the
intermediate region 125-145 GeV
Event preselection Same charge di-lepton
from Ws (one from H?WW, the other from prompt
W) Suppress SM backgrounds pT (lepton)gt 15
GeV, h lt 1.1/2.0
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Final Selection for WWW
Topological Likelihood discriminant, built on 3
variables per channel
10
Exclusion limit for WWW
Events after Topological Likelihood discriminant
Effect on global combination significant in the
intermediate region (125-145 GeV)
Being improved in p17 with ZH?ZWW and also with
H?ZZ
11

Combined Higgs boson Search _at_ DØ
New channel
With low statistics (0.3 fb-1), the cross-section
factors Data/SM 15 at 115 GeV
9 at 160 GeV With higs statistics (1
fb-1) Data/SM 5 at 160 GeV

Based on our first experiences with Data, can
cdfdØ reach exclusion for a 115 GeV Higgs with
2 fb-1 of data, as early simulation studies
were expecting ?
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Expected Improvements _at_ DØ

• Jet energy resolution (recalibration track-jet
  algorithm)
• Subtract expected energy deposition in cal
• Add the track momentum
• Add the energy of out-of-cone tracks
• Improve the jet energy resolution by 20
• Use improved calorimeter calibration
• Z? bb to calibrate b-jet response
• L1-cal Trigger (DØ Upgrade)
• Important for difficult channels ? efficiency
  improvement (ZH?nnbb, hbb)
• Addition of SMT Layer 0 (DØ Upgrade)
• r_at_L1 2.7 cm ? r_at_L0 1.6 cm
  ? better impact parameter
  resolution
• redundancy in pattern recongnition
  for higher luminosity reduce
  fake track
• Keep performance if degradation of Layer 1 due
  to radiation damage
• ? further b-tag improvement (15)

• New b-tagging tool at DØ (bh)
• Combines various variables from the track based
  b-tagging tools in a Neural Network, trained on
  Monte Carlo
• Performance measured on data
• Substantial improvement in performance over
  constituent input b-taggers
• Increase of 33 in efficiency for a fixed fake
  rate of 0.5

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Sensitivity Prospects extrapolated from 0.3 fb-1
results
On the Horizon

• Will 6 times more lumi take our x-section factors
  at 115/160 GeV of 15/9 down to 1?? Maybe..
  with analyses improvements under work in CDF and
  DØ ? Close !

Equiv Lumi gain (_at_115)
Xsec Factor Xsec Factor
Ingredients (DØ)
mH115 GeV mH 160 GeV
Today with 330 pb-1
-
15 9
6.0
6.1 3.7
Lumi 2.0 fb-1
NN b-Tagger/L0
3.0
3.5
NN analysis selections
1.7
2.7 2.8
Dijet-mass resolution
1.5
2.2
Increased Acceptance
1.2
2.0 2.5
New channels
1.2
1.9 2.1
1.7
Reduced Systematics
1.2
1.2 1.5
Combine DØ and CDF
2.0
(assuming similar improvements at DØ and CDF)

• At 160 GeV needs 5 fb-1

• At 115 GeV needs 3 fb-1

? 95 CL exclusion for mH 115-185 GeV with 8
fb-1
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Combining Higgs boson Searches
Combination Procedure
CDF uses a Bayesian approach
DØ uses the CLs (LEP) Method the CLS
confidence interval is a normalization of CLSB
CLSB signal bkgd
hypothesis, CLB bkgd only hypothesis
CLS CLSB/CLB CLSB CLB are defined
using a test statistic Test statistic used
is the Log-Likelihood Ratio (LLR-2 ln Q)
generated via Poisson statistics
(Qe-(sb)(sb)d/e-bbd) s,b,dsig.,bkd,data)
Tevatron Higgs combination is done with both
methods ? they give results compatible within 10.
15
Tevatron SM Higgs Combination
All CDF and DØ results now combined for the first
time ?
mH Limit/SM (GeV) Exp. Obs. 115 7.6
10.4 130 10.1 10.6 160 5.0 3.9 180
7.5 5.8
Note the combined result is essentially
equivalent to one experiment with 1.3 fb-1,
since both experiments have complementary
statistics at low and high mass ? we are
indeed already close to the sensitivity required
to exclude or evidence the higgs at the
Tevatron
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Low mass, use Z ? bb
4.4 sigma evidence based on about 300 pb-1 of
data, shown at ICHEP. Rate consistent with SM
production.
After double b-tag and shift correction
MC 83.3 GeV 13.0 GeV
17
SUSY Higgs
New channels released at ICHEP bh ? b tau tau
? (3 evts vs 6.3 - 0.6) Need to combine
with bbb and h?tautau Note p17 available or
close for these channels btautau also getting
prepared
H started, to be done with top group
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Manpower Issues
Team work to provide best combination, we are
strengthening p17 teams and form p20
teams. Enquiry sent around to the group, to find
out about new students 12 institutions have
answered with new students ? there wont be one
topic per student, rather teams of 1-3
student1-2 postdoc per channel, and use
different timescale (2 milestones per years). SM
Channels WH, ZH (nunu), ZH (ll-), WW,
WWW, tau-channels. SUSY
Channels h? tautau, bbb, btautau,
H direct, H indirect. BMSSM higgs
H, TC, .
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Summary
Conclusions

• First time with essentially complete result
• All channels have been analyzed with
  0.3-1 fb-1 of data
• Full impact of systematics uncertainties is
  included
• Analyses are steadily improving due to
  optimization, already close to the Prospective
  reports
• Combined limit looks very promising
• Our outlook for the future looks very interesting
• LHC experiments will have to work hard to get the
  signal before Tevatron, if the Higgs is light
  (lt130 GeV)
• But the Tevatron has insight also if it is close
  to 160 GeV and can exclude at 95CL from 115 to
  185 GeV.
• Barring accidents, the Tevatron could have
  evidence by 2009-2010, if its there
• But we need to be fast and clever in analyzing ?
  more efforts are needed, input of seniors is
  welcome !!
• Besides all analyzers, I would like to thank
  Suyong and Kazu for excellent collaboration, and
  welcome Sasha Khanov