Transcript Document 7300608

Higgs searches and Top properties at CDF
Takasumi Maruyama (Univ. of Tsukuba)
for CDF collaboration

Contents
 Direct


Higgs searches
Direct SM Higgs searches
Direct Higgs searches for MSSM
 Recent

results of Top physics (except mass)
ttbar resonance search, cross section, lifetime, etc
 Summary
Integrated luminosity (/fb)
Standard Model Higgs Search
• Electro-weak precision data prefer light SM Higgs (as
shown in previous talk, blue-band plot shown above)
(* SUSY requires light Higgs.)
• TeV studies in 1999 and 2003 predicted:
•2 fb-1: 95%CL exclusion at mH=115 GeV/c2
•5 fb-1: 3s evidence at mH=115 GeV/c2
• If Higgs mass is small, TeV could compete to LHC.
SM Higgs Boson Production and Decay @ TeV
Decay Branching Ratios
Production Cross-Sections
bb
H0bb
Z
u
d
u
Z*
e
H0bb
d
u
e+
e
W+
e
u
WW
u
d
u
W+
d
u
u
Direct SM Higgs Search
Associate production (search for Mbb peak)
CDF (and D0) have started the hunt
(WW* result updated from LP05)
Direct production
(phi of dilepton)
SM Higgs Searches at the Tevatron: WHlbb
(Y.Ishizawa (Univ. of Tsukuba) Ph.D thesis (2005))
Select events with
• Identified electron or muon
ET>20 GeV, isolated
• Missing ET > 20 GeV
• Two jets with || < 2.0,
ET>15 GeV.
• Veto extra jets, Z0, cosmics,
conversions, extra isolated
tracks
• At least one b-tag
control signal
region region
control
region
All requirements except # jets.
1, 3 & 4-jet bins are control
samples for normalizing
backgrounds.
WHlbb Channel: Before and After the B-tag
Before b-jet identification; there are different background
composition fraction, but gives higher statistics test !!
WHlbb Channel: Observed and Expected Limits
The gg  H  W+W- Channel
Signal Process:
Dominant background:
qq  W+W-
• Interesting Angular
Correlation due to
Scalar nature of Higgs Boson
• Different from SM W+W- bg
decay angular correlation!


W+
W-
e+
e-
gg  H  W+W- Channel  Discriminant
Variable
•
•
•
•
•
•
Two leptons, Each with ET>20 GeV
Jet Veto to remove t-tbar
Missing ET>25 GeV
Z veto
mll<mH/2 -- note: background depends on test mass
Acceptance is ~0.4% [including Br2(Wl)] for mH>160 GeV
assuming 160 GeV/c2
Summary plot for direct SM Higgs searches
K.Kobayashi (Univ. of Tsukuba)
Ph.D (2005)
Same colors correspond to same decay mode !!
(We have 3 lines, for CDF, D0 and theory)
Ratio of Limits to SM
Note; all are normalized to the theoretical cross section
So How Do We Get There??
Luminosity Equivalent (s/b)2
Improvement
Start with
existing
channels,
add in ideas
with latest
knowledge
of how well
they work
(under
studying)
WHlbb
ZHbb ZHllbb
Mass resolution
1.7
1.7
1.7
Continuous b-tag (NN)
1.5
1.5
1.5
Forward b-tag
1.1
1.1
1.1
Forward leptons
1.3
1.0
1.6
Track-only leptons
1.4
1.0
1.6
1.75
1.75
1.0
WH signal in ZH
1.0
2.7
1.0
Product of above
8.9
13.3
7.2
CDF+DØ combination
2.0
2.0
2.0
17.8
26.6
14.4
NN Selection
All combined
Expect a factor of ~10 luminosity improvement per
channel, and a factor of 2 from CDF+DØ Combination
Expected Signal Significance CDF+DØ vs Luminosity
It’s possible to be lucky or
unlucky!
per experiment
mH=115 GeV assumed
per experiment
Non-SM Higgs: Abb and Att

Supersymmetry (MSSM):


2 Higgs doublets => 5 Higgs bosons: h, H, A, H±
High tanb:



A degenerate in mass with h or H
Cross sections enhanced with tan2b due to
enhanced coupling to down-type quarks
Decay into either tt or bb:



BR(A tt) ≈ 10%, BR(A bb) ≈ 90%
Exact values depend on SUSY parameter space
Experimentally:


pp  Ab+X  bbb+X (D0 has result)
pp  A+X  tt +X
(CDF has result)
•C. Balazs, J.L.Diaz-Cruz, H.J.He, T.Tait and C.P. Yuan, PRD 59, 055016 (1999)
•M.Carena, S.Mrenna and C.Wagner, PRD 60, 075010 (1999)
•M.Carena, S.Mrenna and C.Wagner, PRD 62, 055008 (2000)
CDF search for A->tt using Mvis
Invariant mass of
visible t+t- decay products
plus Missing ET
Limits on Cross-Section * Branching Ratio
 = h0, A0 or H0 or a sum of states with similar masses
Interpretations in MSSM Benchmarks
|| = 200 GeV
M2 = 200 GeV
Mgluino = 0.8 MSUSY
MSUSY = 1 TeV, Xt = √6 MSUSY (mhmax)
MSUSY = 2 TeV, Xt = 0 (no-mixing)
D0 searched A->bbX mode. CDF new result A->bbX coming soon
LEP Limits – mtop=174.3 GeV for historical reasons.
Tau Channel Prospects for the Future
Top Quark Properties
W helicity
Top Mass
•
•
•
Understanding on
top quark properties
has been largely
improved by much
higher statistics
than Run1 (~7 times
at this winter
conferences)
Any significant
deviation from
standard model
prediction could
indicate new
physics.
Recent hot topics
(pink boxes) are
shown at this talk
l+
Top Width
Production
cross-section
Resonance
production
Top lifetime
W+
CP violation
Top Charge
p

t
Production
kinematics
ttbar Spin
correlation
Anomalous
Couplings
b
X
_
_
p
t
_
b
q
Rare/non SM Decays
W-
Branching Ratios
|Vtb|
_
q’
Top Production & decay
Cacciari et al
JHEP 0404:068 (2004)
Kidonakis et al
PRD 68 114014 (2003)
Top pairs via strong interaction
mt (GeV)
85% qq 15% gg
Top decays to W+b by ~100% in SM
dilepton
lepton + jets
all hadronic
BR
~5%
~30%
~65%
background
low
moderate
high
TeVatron √s=1.96 TeV
-PDF NLOσ(pb) +PDF
170
6.8
7.8
8.7
175
5.8
6.7
7.4
180
5.0
5.7
6.3
Top Pair Production Cross Sections
• Cross section is sensitive to both the
production and decay anomaly.
• The difference of the xs with different
decay mode is sensitive to the new physics
such as charged Higgs.
Cross section is old but also fresh topic.
• CDF measure this with various decay
mode and techniques (consistent with SM)
Does something new produce ttbar?
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
This is more direct exotic
search on ttbar production.
Search for new massive
resonance decaying to top
pairs such as top-color Z’



Using lepton+>=4jets (nobtag) sample. Likelihood
incorporating LO matrix
element was used to
reconstruct Mttbar.
Constraint top mass =
175GeV/c2
Fix most of SM backgrounds
to expected rate

Use theory prediction of 6.7pb
for SM top pair production
Interesting fluctuation, ~500GeV
@ 319pb-1 (2005 summer)
New results for Mttbar (with 680pb-1)
• Using the 682pb-1, same analysis was done !! (same selection, same
mass fitting). Note; previous 318pb-1 data is the sub-sample of the full
dataset.
• No excess was observed at this time. (left figure)
• limit on a narrow leptophobic Z’ (GZ’=1.2%MZ’): MZ’>725 GeV at 95%CL
kinematics for ttbar events
• So far, Leading-Order MC (such as PYTHIA, HERWIG) describes
kinematics of the ttbar rich data sample well.
• For example, plots below show PT(ttbar), and PT(top/anti-top) using
ttbar kinematic fitter. (same one as the mass analysis)
• This is the start point of the precision measurement for top quark
Top Lifetime (1)
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SM top has t~10-24s
Measuring lifetime
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
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Helps in confirming SM top
Sensitive to production mechanism
from long lived particles
CDF uses Lepton+Jets channel with
b jet tagged

Measure lepton impact parameter
(d0)
Signal template

Backgrounds:


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Prompt: W+jets, Drell-Yan, Diboson
Displaced lepton: W(Z) decaying to t,
Semileptonic b,c decays, photon
conversion (failing filter)
Calibration: use DY near Z resonance
to get d0 resolution
Top Lifetime (2)


Observed data prefer 0 m lifetime (left figure)
Interpretation to 95% CL.
 Using
 cttop
Feldman-Cousin limit (right plot)
< 52.5 m (t<1.75x10-13 s) at 95% C.L.
Summary (1)
• We have preliminary searches in a great variety
of channels, most with ~300 pb-1 of data analyzed for
2005. (expect ~1000pb-1 results in this summer)
SM Higgs Searches
MSSM Higgs Search
• The sensitivity is currently insufficient to test
for presence or absence of a SM Higgs boson but we
will get more data and improve our channels with wellunderstood techniques.
• We have tools to estimate the sensitivity, also to combine
them
• MSSM Higgs searches are getting exciting.
Summary (2)




Top physics are now in the precision measurement
phase. (more than ~7 times statistics of CDF run I in this
winter.) In this summer, we will have ~1000pb-1 results
Trying to check many of top properties.
So far we have no obvious anomalies against SM in
ttbar rich sample.
If we have physics beyond Standard Model related to
top physics, it could be possible to observe it before LHC.
Backup slides
SECVTX B-tag efficiency
• s/b tradeoff: Leptons & Missing ET are distinctive; real
backgrounds have two b quarks. Single-tag is enough.
Future: Combine single and double-tag analyses, do a tight-loose
tag.
• Jet-probability tags are available but not yet used in Higgs analyses
-- more complication for estimating mistags
Mistag rates typically ~0.5% for
displaced vertex tags
NN Extension of SECVTX B-tag
non-top backgrounds (single-top) Neural Network
after SecVtx ¼ 50%
Signal:
single-top,
Approach:
Background:
•require SecVtx
, Mistags
(mixed acc. to background estimation)
events
• improve purity by including:
• long lifetime (also by SecVtx)
• decay length of SecVtx
• D0 of tracks
• large mass
• mass at SecVtx
• pT of tracks w.r.t jet axis
• decay multiplicity
• # of tracks
• decay probability into leptons
• # of leptons
1200
Signal
Background
1000
800
600
400
200
0
-1
-0.5
0
0.5
1
network output
Dijet Mass Resolution Improvements
• Larger jet cones
• track-cluster
association
• b-specific
corrections
• Advanced
techniques
(NN, “hyperball”)
Target: 10%
resolution for
two central jets
Forward Electrons
Currently plug electrons
only used as a Z0 veto
in the lvbb channel.
Wbb

Phoenix electrons give
25% extra signal
40% extra background
WH

(s/b)forw = 0.6(s/b)central
Not optimal to add -- treat as separate
channel!
Improvement example: Lepton Selection

Forward leptons: factor 1.3


Current analyses use only up to
||<1.1
Electrons:

CDF:





Forward electrons used
already by other analyses,
e.g. W charge asymmetry
Up to ||<2.8
Central electrons: recently
improved efficiency from
80% to 90%
Factor 1.34 in acceptance
W electron charge asymmetry
PRD 71, 051104 (2005)
Muons:

CDF:
uses only up to ||<1.0
can be extended since we
have detector.
~75% efficiency
35 < ETelectron < 45 GeV
EJet Scale & Resolution: Status / Improvements
Jet energy scale uncertainty:
• precision measurements (Mtop), searches
• now ~2.5% uncertainty for jets in top decays
• further improvements:
• generators, higher order QCD
• better scale for ET > 100 GeV region
• complete by end of this year
0.2
Mhiggs = 120 GeV
0
Jet energy resolution:
• currently 17%, goal 10-11%
• further improvements:
• combine track, calorimeter Info: 2%
• expand cone size: 2%
• b-jet specific corrections:1-2%
• sophisticated algorithms: 1-2%
• complete by spring 2006
Raw
1.0
0
0.2
50
100
150
200
250
Scale Corrections
Resolution Improvements
1.0
0
0
50
100
150
200
H --> bb mass (GeV)
250
The Higgs Bosons of the MSSM
• Two Complex Higgs Doublets! Needed to avoid
anomalies.
• Five Degrees of Freedom plus W+,-, Z0 longitudinal
polarization states
• Five scalars predicted: h, H, A, H+, H• CP-conserving models: h, H are CP-even, A is CP-odd
• Independent Parameters:
• mA
• tanb = ratio of VEV’s
• 
• MSUSY (parameterizes squark, gaugino masses)
• mgluino (comes in via loops)
• Trilinear couplings A (mostly through stop mixing)
• Map out Higgs sector phenomenology – variations of
all other parameters correspond to a point in this space
• And a real prediction: mh <~ 135GeV Let’s test it!
Couplings of MSSM Higgs Bosons Relative to SM
W and Z couplings to H, h are suppressed relative to SM
(but the sum of squares of h0, H0 couplings are the SM
coupling). Yukawa couplings (scalar-fermion) can be enhanced
Higgs Boson Production Mechanisms
0
+
t
0
b
Amplitude  1/tanb
suppressed!
b
0
Amplitude  tanb
enhanced!
And many other diagrams
At high tanb, s(h,A+X)  tan2b
b
Amplitude  tanb
(low tanb and SM case: cross-sections
too small to test with current data.)
enhanced!
Higgs Boson Production and Decay at High tanb
• Interesting feature of many MSSM scenarios (but not
all!):
[mh ,mH]  mA at high tanb (most benchmark scenarios..)
• At leading order, G(A0bb) and G(A0t+t-) are both
proportional to tan2b.
• Decays to W, Z are not enhanced
and so Br. falls with increasing tanb (even at high mA)
• Br(A0 bb) ~ 90% and Br(A0t+t-) ~ 10% almost
independent of tanb (some gg too).
MSSM Higgs Searches
Accepted by PRL, hep-ex/0508051
|| = 200 GeV
M2 = 200 GeV
Mgluino = 0.8 MSUSY
MSUSY = 1 TeV, Xt = √6 MSUSY (mhmax)
MSUSY = 2 TeV, Xt = 0 (no-mixing)
CDF Preliminary
310 pb-1
Update plan in near future

All updates aim to have 700~1000pb-1
 WH

Aiming to have results until this May
 ZH

H

-> nu+nu+bbbar;
Aiming to have results around summer
 ZH

-> l+nu+bbbar;
-> ll+bbbar;
They aim to have result in Spring/summer 2006
-> WW*;
Spring/Summer 2006
CDF is very active to get new result !!