Transcript Slide 1

SM HIGGS SEARCHES AT THE
TEVATRON
CDF
Nikos Varelas
University of Illinois at Chicago
http://www-cdf.fnal.gov/physics/exotic/exotic.html
http://www-d0.fnal.gov/Run2Physics/higgs/
CTEQ Meeting, Jefferson Lab
Nov 2005
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Outline
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Introduction
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Understanding the background processes
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Z  bb
W+Jets
Z+Jets
s(Z+b)/s(Z+jet)
Wbb Production
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WH and ZH Associated Production
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Low Mass SM Higgs Searches:
High Mass SM Higgs Searches:
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EW Constraints on the Higgs Mass
Data Samples – Tevatron Run II
Strategy for SM Higgs Searches
H  WW*
WH  WWW*
Prospects & Summary
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Guidance from EW Fits
Tevatron (future): Dmt=1.5 GeV, DMW=30 MeV
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Direct searches by LEP on SM Higgs
Boson:
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mH > 114.4 GeV (95% CL)
Indirect limit from fits to precision EW
measurements from LEP-SLC-Tevatron
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mH < 206 GeV (95% CL)
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using previous mt=174.3  3.4 GeV (Run
I+II)
Latest value: mt=172.7  2.9 GeV (Run
I+II)
+52
 Expected value: mH = 98
−36 GeV
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Run II will provide stringent constraints
to SM Higgs
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dMt ~ 2 GeV with ~2 fb-1
dMW < 30 MeV (currently 59 MeV – Run I
combined)
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 Light Mass Higgs favored
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Fermilab TeVatron - RunII
Chicago

p
p
1.96 TeV
Booster
p
CDF
DØ
Run I
1992-1996
ECM = 1.8 TeV
~120 pb-1
(0.63 TeV ~600 nb-1)
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Tevatron
p source
Main Injector
& Recycler
4
p
Run IIa
2001-2006
ECM = 1.96 TeV
~ 1.3 fb-1
Run IIb
2006-2009
ECM = 1.96 TeV
~8 fb-1
CTEQ Meeting @ JLab
Data Sample
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Tevatron performs according to design
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Record peak luminosity ~ 1.6 x 1032
Record integrated luminosity ~ 21 pb-1 /week
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2002-2004 ( <400 pb-1 )
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Expected luminosity to each
experiment
~8 fb-1
by the end of 2009
Data samples presented here:
Detector data collection efficiency 85-90%
Total Luminosity (fb-1)
9
8
Design
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6
5
4
We Are
Here
Base
3
2
1
0
10/1/03
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9/30/04
9/30/05
9/30/06
9/30/07
9/29/08
9/29/09
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SM Higgs Production and Decay
Production
Decay
Excluded at LEP
s  1.96 T eV
Search strategy:
MH <135 GeV associated production WH and ZH with Hbb decay
Backgrounds: Wbb, Zbb, top…
MH >135 GeV gg H (or WH) production with HWW* decay
Backgrounds: WW/WZ production…
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Low Mass SM Higgs Searches
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WH  e(m)n +bb
ZH  (ee/mm)nn + bb
Measurements rely on
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Based on signed impact parameter
resolution
Jet Lifetime Impact Parameter algorithm
Based on decay length resolution
Secondary Vertex Algorithm
b-tagging
Lepton identification +
Missing-ET resolution
Dijet mass resolution and
light/b-jet calibration
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b-tagging
Z  bb
(Signed) Track
Impact Parameter
Hard Scatter
B
Decay
Length
Understanding of backgrounds
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W/Z + heavy-flavor/light jets
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Z  bb
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Dijet invariant mass of ~86K
events
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CDF
Only two jets in the events (veto
other jets with ET > 10 GeV)
Jets must be back-to-back
(Df>3.0)
Both jets have a secondary
vertex b-tag
The background shape is
computed using untagged data
passing the same selection
The Zbb shape is simulated
with PYTHIA
The two shapes are fit to the
data (blue points)
Fit results are shown in red
Statistical errors only
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s(W(en) + n jets)
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Based on 127 pb-1
Jets
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PT > 20 GeV, |h|<1.1
W’s
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ET > 15 GeV, |h|<2.4
Cone Alg, Rcone = 0.4
Electrons
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CDF
Missing ET > 30 GeV
Veto Z mass region
Theory: Alpgen+Herwig
(+Detector Simulation)
Backgrounds (3-40%)
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QCD
Wtn, top, Z
multiple pp interactions
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*
s(Z/g (ee)
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Based on 343 pb-1
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1,646 Z+jets events
1st Jet
Jets
2nd Jet
Selection:
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+ n jets)/sZ/g*
ET > 20 GeV, |h|<2.5
Midpoint Alg, Rcone = 0.5
3rd Jet
ALPGEN+PYTHIA
(+Detector Simulation)
(CTEQ5L)
Electrons
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PT > 25 GeV, |h|<1.1

75 < Mee < 105 GeV
Z’s
Background (2-5%)
Final cross section ratios are
corrected at the hadron
level
Good agreement with Theory:
MCFM (NLO up to Z+2 partons)
ME-PS (MADGRAPH + PYTHIA
with matching)
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s(Z+b)/s(Z+jet)
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Analysis combines Zee and
mm channels
Based on 180 pb-1
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3,458 Z+jets events
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At least one Jet:
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ET > 20 GeV, |h|<2.5
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PT > 15 GeV, |h|<2.5/2.0
b-PDF is important for hb and
single-top production
2 Electrons/muons:
Z mass cut
Apply sec. vertex b-tag
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Z+heavy flavor is background to ZH
Z+b probes the b-quark PDF
Selection:
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42 events with 1 tag
8.3 events from QCD
background
Measure inclusive ratio to
cancel many systematics
PRL (94), 161801 (2005)
Measurement:
s(Z+b)/s(Z+j) = 0.0210.004(stat)0.002(sys)
Good agreement with NLO QCD: 0.018
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Search for W(en)bb Production
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Dominant bkgd for WH
Based on 382 pb-1
Selection:
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2 Jets:
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ET > 20 GeV, |h|<2.5
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PT > 20 GeV, |h|<1.1
b-tag:
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JLIP (Jet Lifetime Probability)
153 events with 1 b-tag
13 events with 2 b-tags
1 electron:
Missing ET > 25 GeV
Expect 4.29 ± 1.03 Wbb
0.14 ± 0.03 WH
5.73 ± 1.45 WZ, tt, W/Z+jets,
single top, multijets
Total
10.2 ± 2.4 events
Observe 13
95% CL upper limit:
s(Wbb) < 4.6pb
for b-jets with pTb > 20 GeV,
|hb| < 2.5, and DRbb > 0.75
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From Wbb to WH
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Based on 319 pb-1
Selection (en and mn channels):
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2 Jets:
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1 electron or muon:
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CDF
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ET > 15 GeV, |h|<2
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PT > 20 GeV, central
Missing ET > 20 GeV
b-tagging: Secondary Vertex
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WH Limits
CDF
In the absence of a signal, 95% C.L. limits are set on Higgs
boson production cross section times branching ratio to bquarks
DØ previous Wbb/WH Result – 174 pb-1
PRL (94), 091802 (2005)
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Z(nn)H(bb) Search (1)
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An important channel for low-mass Higgs
search
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Trigger on events with large missing HT
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Large B(Znn) ~ 20%
HT is defined as the magnitude of the
vector sum of jets’ ET
Analysis was based on 261 pb-1
Selection:
PTtrk = – |SpT(trk)|
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2 Jets:
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HT
PT.2trk
Jet1
To reject tt events
Reduce “instrumental” backgrounds
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ET
PTtrk
To reject leptons from W/Z
HT = S|pT(jets)| < 200 GeV
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… tracks
= – |SpT(trk in dijet)| … tracks in jets
Missing ET > 25 GeV
Veto events with isolated tracks (pT>8 GeV)
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ET > 20 GeV, |h|<2.5
PT,2
trk
Jet2
Jet acoplanarity Df(dijet) < 165
Use various missing energy/momentum
variables
Form asymmetry variables
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Z(nn)H(bb) Search (2)
No b-tag
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Single b-tag
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Double b-tag
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Z(nn)H(bb) Search (3)
Mass (GeV)
Window
105
[70,120]
115
[80,130]
125
[90,140]
135
[100,150]
Data
4
3
2
2
Wjj/Wbb
32
Acceptance (%)
0.29  0.07
0.33  0.08
0.35  0.09
0.34  0.09
Zjj/Zbb
31
Total bkgd.
2.75  0.88
2.19  0.72
1.93  0.66
1.71  0.57
Instrumental
16
Expected limit (pb)
8.8
7.5
6.0
6.5
Top
15
Limit @95% C.L. (pb)
12.2
9.3
7.7
8.5
WZ/ZZ
6
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Bkgd. composition (%)
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Z(nn)H(bb) Search (4)
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Analysis was based on 289 pb-1
Selection:
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2 Jets:
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Control Regions:
Blind analysis technique
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1st jet ET>40 GeV, 2nd jet ET>20 GeV
Missing ET > 70 GeV
At least 1 b-tag
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CDF
QCD + heavy flavor
EWK, Top, and QCD
Signal Region:
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Veto events with leptons
Higgs mass: 120 GeV
Missing ET and 2nd leading jet are not in Bkgd: 4.36 events
parallel
QCD: 11.4%
Cut optimization is performed in this
Top : 20.5 %
region based on MC simulation before
EWK: 18.2 %
looking at the real data
Mistagged light flavor : 50 %
Observe: 6
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High Mass SM Higgs Searches
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gg  H  WW*  ℓ+ℓ-nn
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B(H  WW*) > 0.9 for mH > 160 GeV
WH  WWW*
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Fermiophobic higgs enhances sB
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High B(h  WW*) for mh > 100 GeV
Measurements rely on
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Lepton identification + Missing-ET resolution
Understanding of backgrounds
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WZ & WW production
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gg  H 
WW*
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ℓ+ℓ-nn
(1)
CDF
Bkgd: Z/g*, WW, ZZ, WZ, tt,
W/Z + j, QCD
Selection:
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2 high-pT leptons + E̸T
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ee, mm, & em combined
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Z and energetic jets
Veto on
WW Cross Section Measurements (pb)
Low (<MH/2) dilepton inv mass
Opening angle between leptons
is useful discriminating
variable

+4.3
+1.2
DØ: 13.8-3.8 (stat) - 0.9 (sys )  0.9(lum ) (25 evts)
+5.8
+1.8
CDF: 14.6-5.1 (stat) -3.0 (sys )  0.9(lum ) (17 evts)
Two leptons tend to move in
parallel due to spin correlation
of Higgs boson decay products
n
W+
e
n
W-
e-
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NLO Theory:
+
CDF: PRL (94),
12-13.5 pb
211801
(2005)
DØ: PRL (94), 151801 (2005)
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gg  H 
*
WW

+
ℓ ℓ nn
(2)
CDF
s*BR(H→WW) < 3.7pb
DØ
For MH=160 GeV
Analysis based on ~320 pb-1
Number of expected events for MH=160 GeV:
0.68 ± 0.01 HWW*
12.3 ± 0.3 Diboson Production
2.8 ± 0.9 W+jet/g
4.0 ± 0.7 Z/g*
0.47 ± 0.03 Top
0.2 ± 0.1 multijets
Total
19.7 ± 1.2 events
Observe 19
DØ: Submitted to PRL
hep-ex/0508054
Maximum likelihood limit on
the Dll distributions for
mH=140-180 GeV
CDF
Analysis based on ~360 pb-1
Number of bkgd events for MH=160 GeV:
0.58 ± 0.04 HWW*
9.79 ± 1.03 WW
13.78 ± 1.24 Total bkgd
Observe
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WH  WWW* 
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±
±
ℓ nℓ’ nqq’
(1)
CDF
Search for associated Higgs
production with W where the
HWW*
Selection:
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2 like-sign high-pT leptons
Veto events with a 3rd high-pT lepton
Significant E̸T
DØ
Analysis based on ~370 pb-1
Data: 1/3/2 events for ee/em/mm channels
bkgd: 0.70 ± 0.08 for ee
4.32 ± 0.23 for em
3.72 ± 0.75 for mm
CDF
Analysis based on ~190 pb-1
Data: 0 events
bkgd: 0.95 ± 0.61(stat) ± 0.18(sys)
SM Higgs (160 GeV) expected to be ~0.03 evts
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WH  WWW* (2)
CDF
CDF: 190 pb-1
DØ: 370 pb-1
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Where we Stand Today
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CDF
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SM Higgs Search Prospects

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Near term: expect at least doubling of analyzed data for
Spring ’06 conferences
Long term: reaching ~8 fb-1 by 2009

Detector upgrades in Spring 2006 (Si (DØ), trigger/DAQ (DØ, CDF))
LEP
Tevatron Higgs Sensitivity Group:
Initial Report: hep-ph/0010338 (2000)
Updated in 2003 in the low Higgs mass
region: Fermilab-PUB-03/320-E
2009
http://www-d0.fnal.gov/Run2Physics/higgs_sensitivity_study.html
• WHlnbb
• ZH nnbb
• Improvement due mainly to
sophisticated analysis techniques and
better detector understanding
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How do we Compare to HSS-03?
Ratio
Dijet mass window
DØ Analysis
(PRL ‘05)
174 pb-1
WH enbb
[85,135]
Prospective
Study (‘03)
normalized to
174 pb-1 and to
WH bben
[100,136]
Prospective
DØ Analysis
R=0.72
Dijet mass resolution
14 ± 1 %
10 %
R=0.71
Signal events (S)
0.049
0.145
R=3.0
Background evts (B)
1. 07
1.76
R=1.6
S/B
0.045
0.11
R=2.4
We are missing a factor 2.4 in sensitivity
for this WH(e) channel.
A factor of 50 is needed to reach SM
expectations for ~115 GeV higgs
(or ~450 fb-1 of luminosity!)
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So How Do We Get There?
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Use forward electrons (+30%),
Better EM-ID (+30%)
Higher b-tagging efficiency (+40%)
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Layer-0 upgrade, NN b-tagger
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Improved di-jet mass resolution (+40%)
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Better calorimeter calibration, use Cal-Track jets
We can reach the expected sensitivity by Summer’06
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Additional factors not included in WH sensitivity:
3 (leptons) * 2 (experiments) * 2.5 (channels) * 1.8 (NN-selec) * 12
(lumi  2fb-1) = 324 = 182
 Combining both factor 2.4*18 =43  consistent with 50 needed to
reach SM expectations for ~115 GeV Higgs
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Summary
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Tevatron accelerator complex and
experiments are performing well
Higgs searches using 400 pb-1 of Run II data
show no deviation from SM bkgd expectations
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Good understanding of W/Z+jets processes
Expect improved analyses and limits by Spring
’06 based on ~ 1 fb-1 of data
Sensitivity to mH>114 GeV starts with 2 fb-1
Exclusion up to mH ~ 180 GeV with 8 fb-1
Very exciting short and long term future
prospects with a lot of hard work ahead
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