Transcript Higgs Searches at the Tevatron Chris Tully Princeton

Higgs Searches
at the Tevatron
Chris Tully
Princeton
On behalf of the CDF/D0 Collaborations
SUSY 2005
IPPP Durham, England, July 18-25, 2005
1
Low Energy Supersymmetry

The Higgs Sector is vacuous without it…
Stability of the Electroweak scale is as
fundamental and as deserving a resolution as
Classical E&M arguments were to the instability
of atomic states posed over a 100 years ago.
We can only hope the answer will be equally far
reaching…
2
Preferences from MW and mtop

Error on mtop no
longer dominates
Mtop = 172.7 ± 2.9 GeV
New CDF/D0 Mass
Combination

W self-energy
may be decisive
once MW improves
3
New Top Mass Combination


This includes new
preliminary
measurements
(based on 320 pb-1)
from CDF/D0 which
simultaneously fit
the jet energy scale
with the hadronic W
mass constraint
The correlated
systematical error is
of order ~1.7 GeV
4
SUSY Guidance
• Lightest Higgs mass
compatible with high
tanb region for wide
range of stop mixing
qd
,ℓ–
downtype
h:  sin 
cos b
cos 
H: cos b
sin b
A: cos b
qd,ℓ+
Use tanβ enhancement!
Heinemeyer,
Weiglein
9
LEP
Preliminary
5
Large b-Production

But how well known…
Use Leptonically Decaying Z’s
as a probe!
152-184 pb-1
Z+b
B-hadron
Lifetime tag
PRL 94, 161801 (2005)
6
MSSM Higgs b(b)f Search

b(b)f → b(b)bb f=h/A or H/A

At least 3 b-tagged jets

Data-derived background shape
260 pb-1
at 95% Excl.
Leading
Submitted to PRL
7
b(b)f Limits: tan2β Enhancement
Enhancement depends on loop corrections (Δb)
and SUSY parameters:
2
  BRSUSY
tan b
9
 2   SM 

2
2
1  b  9  1   b 
260 pb-1
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b(b)f Projections
CDF+
Tevatron will
probe below
mt
!
tan b 
mb
1 fb-1
2 fb-1
4 fb-1
8 fb-1
Projection based on
existing analysis:
Doesn’t include proposed
b-tag improvements
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Higgs Decays to t-leptons

t-Identification
Methods (CDF)
Method yields a rich sample
of taus with the expected
visible masses and track
multiplicities from Z→tt
Before
OS req.
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h/H/A→tt Search

Visible Mass is the final
search variable:
H
tanb=30
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MSSM Higgs→tt Search

tanb Exclusion Limits:
b(b)f
12
Higgs→tt Projections
CDF+D0
Assumes several analysis
improvements

Higgs→tt and
b(b)f will reach
similar sensitivities
at the same time
Opens up exciting
prospects for learning
more about SUSY as
yb and yt see different
loop-corrections
13
Charged Higgs from top quark decay

Predicted to substantially modify top quark
Branching Ratios at high and low tanb

Additional sensitivity in lepton + t channel
cs m
+
=
100 GeV
H
tn
*
tb
mH+ =
140 GeV
tn
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H+ tanb Exclusion
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Br(t→H+b) Exclusion for Br(H+→tn)=1

Range of Exclusions Br<0.4 to Br<0.7
depending on MSSM parameters
H+→cs Search in progress… 16
Lightest Higgs Boson
• Lightest Higgs boson is SM-like for large MA
 M A2  M Z2 

tan 2  tan 2b  2
2 
 M A  MZ 
M A  MH  MH
(decoupling limit)
• Given the difficulty of detecting the h→bb decay at
the LHC, the Tevatron provides a potentially essential
probe of this low mass channel
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Low Mass Higgs Search

Maximum sensitivity requires a
combination of CDF/D0 search channels:

WH→ℓnbb, ZH→nnbb & ℓℓbb, WH→WWW*, H→WW
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nbb Search (CDF)
319 pb-1
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enbb Search (DØ)

mnbb in Progress…
Expect
Total
Observe
Tagged Sample
≥1 b-tag
0.14 ± 0.03 WH
4.29 ± 1.03 Wbb
5.73 ± 1.45 tt+other
10.2 ± 2.4 events
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Double-Tagged
Sample
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Missing Energy Channel (CDF)

Two Control Regions:

No Leptons + f(ET, 2nd Jet)<0.4

Min. 1 Lepton + f(ET, 2nd Jet)>0.4 (Top, EWK, QCD)
Control Region 1
(QCD H.F.)
b-jet
Missing ET
y
x
b-jet
• Large ET
• Two jets
(one b-tagged)
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Missing ET
144.8 GeV
Missing Energy Event
(CDF)
Double tagged event
Di-jet invariant mass = 82 GeV
Second Jet ET = 54.7 GeV
Leading Jet ET = 100.3 GeV
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Missing Energy Channel (CDF)
Selection cut
ZH 120 (288.9 pb-1)
Di-jet mass
0.1260.016
cut (100,140)
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Missing Energy Channel (DØ)


Cross-efficiency important

WH→ℓnbb (lost ℓ)

ZH→nnbb
3x Larger WZ/ZZ Signal

Similar dijet bb mass peak
24
WH→WWW* (CDF)
Same-Sign Dilepton Search
2nd Lepton pT
“One Leg”
Photon
Conv.
No Event
Seen
0.03 SM Signal Expected
mH=160 GeV
Fake Lepton Region
Vector pT Sum
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WH→WWW* (DØ)

WWW*→ℓ± ℓ± + X



Same-Sign Dileptons
Important bridge
across 130-160 GeV
“Gap” from H→bb
and inclusive H→WW
CDF 194 pb-1
363-384 pb-1
Background from
WZ→ℓnℓℓ
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H→WW (DØ)
fℓℓ < 2
Leptons from Higgs tend to
point in same direction
Apply fℓℓ < 2
WW cross section measured
+1.2 (sy.) ± 0.9 pb
WW =13.8 +4.3
(st.)
–3.8
–0.9
PRL 94, 151801 (2005) 27
Overview of CDF/DØ SM Higgs
Searches
28
Prospects for SM Higgs Search

Current analyses sensitivities are
lower than used for projections, but
differences appear to be recoverable
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Summary

MSSM tanb enhancement searches




b(b)f & Higgs→tt already sensitive to tanb~50-60
Plans to add b(b)f→b(b)tt
t→H+b, H+→tn results (Plans to add H+→cs)
SM Higgs searches



Full complement of search channels with first results
Will be important to benchmark search sensitivity
with WZ diboson production with Z→bb
~1 fb-1 to analyze by Fall
Combine, combine, combine…
30
Backup Plots &
Tables
31
Tevatron Performance
32
SM Higgs Production Processes
33
Z→bb (CDF)
34
nbb Search (CDF)
35
H→WW (DØ)
36
Improvements to b-tagging

Analysis depends on strongly on b-tag

Neural Net b-tagging
Operating
~ Fake Rate
~b
Efficiency
Tight
0.25 %
44 %
Medium
0.5 %
52 %
Loose
1.0 %
57 %
Loose2
2.0 %
64 %
Loose3
3.0 %
68 %
Loose4
4.0 %
70 %
Point
DØ
37
Z→tt as a benchmark

DØ Neural Network
t-Selection


Variables:
 Shower Profile
 Calorimeter Isolation
 Track Isolation
 Charged Momentum Frac
 Opening Angle
 Etc.
3 Types:
 p-like
 r-like
 Multi-prong
38
Missing Energy Channel (DØ)
• Trigger on event w/ large ET & acoplanar jets
• Instrumental ET backgrounds (Data-driven estimation)
– Asymmetries computed: Asym(ET,HT) and Asym(S pTtrk,pT2trk)
Instr. Background
Data in
Data
from Sidebands(Data) signal region
Signal
Exponential
Signal
Sidebands
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Missing Energy Channel (DØ)
No b-tag
Single b-tag
Double b-tag
40
H→WW (CDF)
Cluster mass:
MC 
p   M
 2
T
2

=184 pb-1
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