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
Introduction
Understanding the background processes
Z bb
W+Jets
Z+Jets
s(Z+b)/s(Z+jet)
Wbb Production
WH and ZH Associated Production
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
Direct searches by LEP on SM Higgs
Boson:
mH > 114.4 GeV (95% CL)
Indirect limit from fits to precision EW
measurements from LEP-SLC-Tevatron
mH < 206 GeV (95% CL)
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
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
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Data Sample
Tevatron performs according to design
Record peak luminosity ~ 1.6 x 1032
Record integrated luminosity ~ 21 pb-1 /week
2002-2004 ( <400 pb-1 )
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)
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8
Design
7
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 Hbb decay
Backgrounds: Wbb, Zbb, top…
MH >135 GeV gg H (or WH) production with HWW* decay
Backgrounds: WW/WZ production…
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Low Mass SM Higgs Searches
WH e(m)n +bb
ZH (ee/mm)nn + bb
Measurements rely on
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
b-tagging
Z bb
(Signed) Track
Impact Parameter
Hard Scatter
B
Decay
Length
Understanding of backgrounds
W/Z + heavy-flavor/light jets
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Z bb
Dijet invariant mass of ~86K
events
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 Zbb 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)
Based on 127 pb-1
Jets
PT > 20 GeV, |h|<1.1
W’s
ET > 15 GeV, |h|<2.4
Cone Alg, Rcone = 0.4
Electrons
CDF
Missing ET > 30 GeV
Veto Z mass region
Theory: Alpgen+Herwig
(+Detector Simulation)
Backgrounds (3-40%)
QCD
Wtn, top, Z
multiple pp interactions
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*
s(Z/g (ee)
Based on 343 pb-1
1,646 Z+jets events
1st Jet
Jets
2nd Jet
Selection:
+ n jets)/sZ/g*
ET > 20 GeV, |h|<2.5
Midpoint Alg, Rcone = 0.5
3rd Jet
ALPGEN+PYTHIA
(+Detector Simulation)
(CTEQ5L)
Electrons
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)
Analysis combines Zee and
mm channels
Based on 180 pb-1
3,458 Z+jets events
At least one Jet:
ET > 20 GeV, |h|<2.5
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
Z+heavy flavor is background to ZH
Z+b probes the b-quark PDF
Selection:
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) = 0.0210.004(stat)0.002(sys)
Good agreement with NLO QCD: 0.018
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Search for W(en)bb Production
Dominant bkgd for WH
Based on 382 pb-1
Selection:
2 Jets:
ET > 20 GeV, |h|<2.5
PT > 20 GeV, |h|<1.1
b-tag:
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
Based on 319 pb-1
Selection (en and mn channels):
2 Jets:
1 electron or muon:
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CDF
ET > 15 GeV, |h|<2
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)
An important channel for low-mass Higgs
search
Trigger on events with large missing HT
Large B(Znn) ~ 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)|
2 Jets:
HT
PT.2trk
Jet1
To reject tt events
Reduce “instrumental” backgrounds
ET
PTtrk
To reject leptons from W/Z
HT = S|pT(jets)| < 200 GeV
… tracks
= – |SpT(trk in dijet)| … tracks in jets
Missing ET > 25 GeV
Veto events with isolated tracks (pT>8 GeV)
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
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Bkgd. composition (%)
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Z(nn)H(bb) Search (4)
Analysis was based on 289 pb-1
Selection:
2 Jets:
Control Regions:
Blind analysis technique
1st jet ET>40 GeV, 2nd jet ET>20 GeV
Missing ET > 70 GeV
At least 1 b-tag
CDF
QCD + heavy flavor
EWK, Top, and QCD
Signal Region:
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
gg H WW* ℓ+ℓ-nn
B(H WW*) > 0.9 for mH > 160 GeV
WH WWW*
Fermiophobic higgs enhances sB
High B(h WW*) for mh > 100 GeV
Measurements rely on
Lepton identification + Missing-ET resolution
Understanding of backgrounds
WZ & WW production
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gg H
WW*
ℓ+ℓ-nn
(1)
CDF
Bkgd: Z/g*, WW, ZZ, WZ, tt,
W/Z + j, QCD
Selection:
2 high-pT leptons + E̸T
ee, mm, & em combined
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 HWW*
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 Dll 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 HWW*
9.79 ± 1.03 WW
13.78 ± 1.24 Total bkgd
Observe
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WH WWW*
±
±
ℓ nℓ’ nqq’
(1)
CDF
Search for associated Higgs
production with W where the
HWW*
Selection:
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
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
• WHlnbb
• 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?
Use forward electrons (+30%),
Better EM-ID (+30%)
Higher b-tagging efficiency (+40%)
Layer-0 upgrade, NN b-tagger
Improved di-jet mass resolution (+40%)
Better calorimeter calibration, use Cal-Track jets
We can reach the expected sensitivity by Summer’06
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
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
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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