Top Quark Properties Top Quark Properties from CDFfrom CDFRobin D. Erbacher

University of California, Davis

Fermilab Wine and Cheese -- Friday June 10, 2005

2

Top Quark Discovery: 1995

The search for top lasted almost twodecades. Its unexpectedly heavy mass delayed discovery.

CDF Run 1

CDF + D0 combined:

Mass (top) = 178 4.3

GeV/c2

5 orders of magnitude

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Why Is Top So Interesting?

Well, top physics is different!

•Top quark lifetime is short: decays before hadronizing

No spectroscopy like other heavy flavor

Top momentum and spin transferred

to decay products

• Probes physics at higher scales than other known fermions

Top (or heavy top) very hip in many

EWSB models: Higgs, Top Color,

Little Higgs, SUSY mirror models

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τ top ~ 10-24 s , Γ−1 ≈ 1.5 GeV( )−1

<< ΛQCD-1 ~ (200 MeV)-1

In Top Color, the Higgs is a bound state of top quarks (C. Hill)

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Elucidating the Top Quark in Run 2

Top pairs: (tt) ~7 pb

•Top production rate•Mass of top•W helicity in top events•QCD tests•New physics in X tt•Anomalous couplings, new particles

Single top: (tb) ~3 pb

•|Vtb|•QCD tests•New physics?

New physics!

New physics!

Vtb

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# of Physicists for Particle Discovery

CDF (Tevatron) ~ 800 (1500)

Year Discovered

Nu

mb

er

of

Ph

ysic

ists

LHC

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Physics of the Top Quark

Top physics is still one of the more sexy things to study at the Tevatron…

7

How is Top Produced?

~15%

g-g

One top pair each 1010 inelastic collisions at s = 1.96 TeV

Standard ModelTevatron Pair Production

Through Strong Interaction

Rarely!!q-q

~85%

pb7.6)175@( ≈=→ GeVMttpp top

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How Else is Top Produced?

Standard Model Tevatron Single Top Production

pb3)175@( ≈=+→ GeVMXtpp top

p

t

t

p

XResonance Production?

Top Color-Assisted TechnicolorOR

?????

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How Does Top Decay?

Main “usable” top event topologies:• tt llbb di-lepton 5% e+• tt lqqbb lepton+jets 30% e+• tt qqqqbb all hadronic 45%

Standard Model:tWb ~ 100%

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What do we look for in top events?

Electrons Muons Neutrinos Quarks (Jets) b Quark Jets

“Lepton + Jets Channel”

W l , W qq ~30%

“Di-Lepton Channel”

W l W l ~5%

“All Hadronic Channel”

W qq, W qq ~45%

Identifying Top Quarks

=> Signature-Based Analyses!

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One of the first things to measure is the top pair production rate.

Why is measuring the rate of top production important?

• Higher cross section than predicted could be a sign of non-standard model production mechanisms

Resonant state X tt OR Anomalous couplings in QCD?

• It could also mean new physics in the top sample!

Production Cross Section

Nevents - Nbackground(tt) Luminosity *

Measuring Top Pair Production

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Finding Top Is Difficult!In Run 1, we likely produced ~500 top quark pairs

at CDF. The problem was finding them. We had only 76 ttbar pairs in our mass sample!

Separating Top from background:•Finding clean lepton samples•Tagging b-jets

–Displaced vertices–Soft lepton tagging (SLT)–Jet Probabilities

•Fitting to kinematical distributions using likelihood or neural network techniques

Traditional CDF

method

HT Distribution for TopEvents vs BackgroundChallenges:

Acceptance for Top(improved in Run 2)

Separating Top Events from W+jets and QCD Backgrounds

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Top Cross Section Measurements(Scorecard)

Separating Top from Background•Identifying clean lepton samples•Tagging b-jets

–Displaced vertices–Soft lepton tagging (SLT)–Jet Probabilities

•Fitting to kinematical distributions using likelihood or neural network techniques

Silicon b-Tagging

162 pb-1 Lepton+JetsPRD 71, 052003 (2005)

Charged Particles

Secondary Vertex

Primary Vertex

Impact Parameter

Lxy

Soft Lepton Tagging

194 pb-1 Lepton+JetsResult Submitted to PRD

Two high PT Leptons

200 pb-1 DiLeptonPRL 93, 142001 (2004)

Top Kinematics:Neural Network

195 pb-1 Lepton+JetsSubmitted to PRD

New Results!! with > 300 pb-1

Jet Probability

162 pb-1 Lepton+JetsConference Result

All Hadronic:B-tags + kinematics

162 pb-1 All JetsConference Result

B-tags + kinematics

162 pb-1 Lepton+JetsPRD 71, 052003 (2004)

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Collected Dataset for CDF

Luminosity collected up until Fall ‘04 shutdown.(Most early 2005 results: 318-347 pb-1)

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Multivariate L+J Cross Section: Neural Network

Method: Use 7 kinematic and event shape variables to discriminate top from background by training a neural network to distinguish events.

Previous Result: 195 pb-1 (PRD) . This Result: 347 pb-1

Total Event Energy HT || Max Jets

16Looks like top!Adding more event information allowsbetter discrimination of top events.

Output of a 7-Input neural network, choosing bothshape and energy variables to discriminate top from bkg

Signal trainedon Pythia ttbar

Background trainedon AlpGen+HerwigW+3 parton MC

Fit to neural network output for top and W+jets background:

Sensitivity similar to b-tagged analysis, but larger sample used

(tt)=6.0 ±0.8 ±1.0 pb

Kinematics to Find Top

Neural network output shape templates for signal, electroweak, and QCD multijet backgrounds, normalized to unit area.

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Kinematic Cross Section Results

In good agreement with theory for Mtop = 178 GeV:(tt)=6.1 ± 0.8 pb (M. Cacciari, et al. JHEP 404, 68 (2004))

Sample Events Fitted tt (tt )

W + 3 jets 936 148.2 20.6 6.0 0.8 1.0 pb

W + 4-Jet 210 80.9 15.0 6.1 1.1 1.4 pb

CDF Preliminary (347 pb-1)

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Keys to Improvement 3 Jets 4 Jets

Effect Acceptance Shape Total Acceptance Shape Total

Jet Et Scale 3.0% 5.4% 8.3% 8.6% 3.3% 11.8%

W+jets Q^2 Scale 10.2% 10.2% 16.0% 16.0%

QCD fraction 0.9% 0.9% 1.8% 1.8%

QCD shape 1.0% 1.0% 2.5% 2.5%

Other EWK 1.0% 1.0% 1.1% 1.1%

ttbar PDF 1.5% 2.9% 4.4% 2.4% 2.3% 4.7%

ttbar ISR 0.4% 1.2% 1.6% 2.0% 0.6% 2.6%

ttbar FSR 0.8% 0.7% 1.5% 0.7% 0.2% 0.8%

ttbar generator 1.7% 0.9% 2.6% 4.4% 0.2% 4.5%

Lepton ID/trigger 1.3% 1.3% 1.3% 1.3%

Lepton Isolation 5.0% 5.0% 5.0% 5.0%

Luminosity     5.8%     5.8%

Total     16.4%     22.8%

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SecVtx B-tagging in Lepton+Jets

New tight SecVtx b-tagger:•Tracking improved in new offline, cuts loosened•Tightened secondary vertex quality requirements•15-20% tag efficiency increase from previous tagger

Event tagging efficiency for ttbar:

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Optimized L+J Cross Section Analysis

Improve Signal, S/sqrt(S+B), B:•Signal: dataset doubled (162 318 pb-1), tagger improved

•S/(S+B): Re-optimize cut on HT as in previous analysis

•Background Error: Reduce error on poorly-modeled QCD fakes by cutting out a lot of these backgrounds: MT(W) cut

HT> 200 GeV Optimal MT(W) > 20 GeV Optimal

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SecVtx B-tagged Cross SectionBackgrounds estimated from data and MC, the traditional

CDF Method 2. Top is excess above these for ≥3 jets.

Sample Events tt Fraction (tt )

1 b tag 138 81% 7.9 0.9 0.9 pb

2 b tags 33 90% 8.7 1.7 1.5 pb

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SecVtx Cross Section SystematicsBackground Errors Reduced with Optimization

Largest systematic remains the b-tagging scale factor (6.6%). The Heavy Flavor fraction, ~50% of background, ~2-3% on cross section.

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SecVtx Double-Tagged Event

The new tagger has provided a clean sample of single- and double-btagged events, which will be useful for single top, top properties, and searches such as for WH.

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CDF Cross Section Results Summary Latest results in Red

Many different approaches to measuring the top cross section, allowing us to carefullycross check the results-- and look for anomalies.

25

Run 1: Excess in the b-tagged Lepton + Jets Sample?

Observed excess of b-tags in the 2 jet bin

Too many SVX double tags (more than one b-tagged jet/event)

Too many multiple tags (more than one b-tag/jet)

A lot of speculation, but nothing solid.

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Understanding Wbb+Jets

Assume efficiencies cancel:

General Method:•Create MC templates for the vertex mass of b, c, light quark jets•Combine tagged MC events, and fit vertex mass distribution from data•Use the pre-tag sample for W+1,2 jets

•Provides cross check on heavy flavor fraction •First step towards measuring Wbb cross section•Will help top properties measurements, and searches for single top, and for Higgs

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(W +bb)

σ (W +1,2 jets)

Use Data to Measure :

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W+bb/W+jj Ratio Results

Vertex Mass Templates fromdata and monte carlo

Fit to b-tagged data, obtain number of observed tags

Use SecVtx backgrounds, pretag estimates from data

Result:

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(W +bb)

σ (W +1,2 jets)= 0.0072 ± 0.0024 ± 0.0022

SecVtx HF Fraction Prediction: 0.012±0.003, 1.3 higherResult will improve with more data and anti-charm tagging

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Top Mass: Current World’s Best

Details: Wine & Cheese April 12th By U.K. Yang

Key Ingredients:•Statistics: Large sample of single and double tagged events•Systematics: Simultaneous fit to top mass and jet energy scale using Wjj decays

27.36.3top GeV/ (syst.) 7.1JES)(stat. 5.173 cM ±+= +

−

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New Top Mass: Updated Dynamic Likelihood Result

Integrateover z1, z2,parton pT

Matrix elementprovides completedynamical event

information

PartonDistributionFunctions

+ ISR Transferfunctionsconnectjets to

partons

Sum overall possiblejet-parton

assignments

wtoptwI I

Tbatopi dsdMIwsMpzzF

FluxML

t s

xy|x );,())((||),,(2

)( 224

δπ+−=∑∑∫ l

Replace pz with

W propagatorfactor

Likelihood for Each Event i

Previously, the best Run 2 result with 162 pb-1

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New DLM Top Mass Result

No ME used for backgrounds. Instead, mapping function used since backgrounds dilute mass in a known manner

Mtop = 173.8 ± 4.2

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DLM Top Mass Systematics

By far the largest improvement has been the reduction in the jet energy scale systematic! 5.3 GeV3.0 GeV

Sources Mtop(GeV/c2)

JES (up to hadron) 2.1

T.F.(up to parton) 2.2

ISR 0.4

FSR 0.5

PDF 0.5

Generator 0.3

bkg fraction (6.7%) 0.6

bkg Modeling 0.6

b tagging 0.2

b jet energy 0.6

TotalTotal 3.3 3.3

Run II 2004

Run I

Fractional Syst. Uncertainty vs PT

Central region

~3% jet PT uncertainty in

top events

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New Top Mass Comparisons

• Complementary methods–Different sensitivity to details of production and decay.

• DLM could in principle implement similar treatment of JES in the joint likelihood.

Method Template DLM

163 pb-1 result 176.7 ± 9.1 (“1D”) 177.8 ± 7.8

318 pb-1 result 173.5 ± 4.1 (“2D”) 173.8 ± 4.2

Selection ≥ 4 jets = 4 jets, ≥ 1 tag

Combinatorics Best 2 Use all

JES Wjj None yet

Background Template Mapping

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CDF Top Mass Summary Two new top mass

results: Best is more sensitive than

the Run 1 combined!

Channel L+Jets Dilepton All-had

Analyses 6 5 2

Mature 2 4 0

Blessed 2 0 0

Renewed Tevatron Top Mass Combo Meeting held June 9th…

Stay tuned!Publications and combination

Coming soon!

On Deck:

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Future for Top Mass Our dominant systematic, the jet energy

scale, now scales with statistics!

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Top Decay Properties

We said tWb, but really 100%?

Indirect measurement using the CKM matrix:

• Elements |Vub| and |Vcb| measured to be very small from decay of B mesons • Unitarity and only three generations implies |Vtb| is 0.998 @ 90% CL

With top quark samples we can measure it directly as “R”:

Use the ability to identify jets with a distinguished secondary vertex: b-tagging

•The number of b-tagged jets depends strongly on R and e

We classify the ttbar sample based on the number of b-tagged jets•The relative rates of events with 0/1/2 b-tags is very sensitive to R

b} s,d,{q e wher)(

)(R 222

2

=++

=→→

≡tbtstd

tb

VVV

VWqtBRWbtBR

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Measuring BR(tWb)/BR(tWq)

•Use the Lepton+Jets and Dilepton samples.

•Total integrated luminosity of 162 pb-1

•Classify samples having 0/1/2 b-tagged jets

•Estimate background contribution to each of the six sub-samples

•MC and data driven (Method 2)•Background Lepton+Jets 0-tags obtained using NN techniques.

•determine the b- c- and q- jet tagging

efficiencies εb, εc and εq; then find efficiency

to have 0,1 or 2 tags in a particular top event.

•get the expected top content in 0/1/2 tags.

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Measuring BR(tWb)/BR(tWq) Compare the expected top with the observed top in the 0/1/2 tag subsets and extract R by maximizing the likelihood.

syst) (stat 12.1R 17.021.013.019.0 += ++

−−

Set F-C lower limit : R >0.61 at 95%CL

|Vtb| > 0.79 at 95%CL(assuming unitarity)

Mild excess in double b-tags sample drives the R value above 1Mild excess in double b-tags sample drives the R value above 1

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”R” Consistent with Standard Model

So…….This means that the top decays to a b

quark most of the time, as expected.

tt

bb??

But, is always a W+ ???

Could be sometimes an H+ ???

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• assume each top quark has 5 possible decay modes

t Wb

t H+b t*bb W+bbb

t H+b τb

t H+b csb

t H+b W+h0b W+bbb•

• Data: use four XS samples– dilepton– lepton+jets (1 tag)– lepton+jets (2 or more tags)

– lepton+τh

Measurement of BR(tH±b)

( )∑=

±=5

1,XSA ,, 0,,,

jihHjijiXSAtt mmwHiggswTopBB εε

from MC

Branching fractionsof each decay mode

∫+= LdtNN XSAttbackXSAXSA ,

exp εσ

from XS meas.

theory=(6.7±0.7)pb (hep-ph 0303085)

~191 pb-1

(CPsuperH, full SUSY EW/QCD corrections)

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Expected Events v. tan() Per Sample

Integrated Luminosity of 171 pb-1

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Limits: MH+ v. tan, Min Stop Scenario

BR’s predicted by MSSM in Minimal Stop Mixing scenario

Typical search for h0 at LEP(hep-ph/9912223).

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What Can We Take from This?

There is no evidence within reach for top decaying to

charged Higgs.

So…….Assume that top decays to W+b.

tt

bbWW++

But, is the nature of the tWb vertex as expected?

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W Helicity from tWb Decays• Examines the nature of the tWb vertex,

probing the structure of weak interactions at energy scales near EWSB

• Stringent test of SM and its V-A type of interaction.

V-A Suppressed

t

W0 Longitudinal fraction

F0

W+1/2

+1/2

0W

W- Left-Handed fraction F-

tb

W

+1/2-1/2

+1

W+ Right-Handed fraction F+

tW

b

+1/2+1

-1/2

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Run 2 W Helicity in Top Events

The combined dilepton and lepton+jets b-tagged eventsplotted against the best fit.

SM: Only longitudinal andleft-handed W’s can be produced in the top restframe.

Use lepton pT spectra todetermine the fractionF0 of longitudinally polarized W’s.

F0 = 0.7 in the Standard Model

Result: F0 = 0.27+ 0.35 – 0.21Or F0 < 0.88 @ 95% CL

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Run 2 W Helicity Using cos*

Both dilepton and lepton+jets

events combined. Combination with pT & F+

underway…

Result: F0 = 0.89 ± 0.32 ± 0.17Or F0 > 0.25 @ 95% CL

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

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What About Production?

Are some of the top-like events from a heavy top?

• We know that, within errors:– The top decays mostly to W+b– The nature of the tWb vertex is what’s expected.

• Measured Production Cross Sections Consistent

with Standard Model, within errors

ttbb

WW++

ttbb

WW++XX

Are some small number of top pairs coming from a resonance?

47

Search for High ET Top-Like Events

HT distribution for W+4p, ttbar, and t' where M(t')=225 GeVWe can set limits on new physics processes in top sample

48

HT Plot with t' Signal, M(t') =225 GeV

Plot for fit result with t' signal included at 95% CL limit

(ttbar) 6.12 pb in this fit]

49

Result: Limits (pb) Versus M(t')

Limits on BR(t'Wq)2

Mtop constraint *

170 7.8 1.0 pb

175 6.7 0.9 pb

180 5.75 0.7 pb

Constraintsvary with assumed

top mass, butnot by much.

Mtop=180

Mtop=170 Expected 1 sensitivity

* Taken from hep-ph/0303085

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Projected Limits: Higher Luminosity

Large improvement in systematic errors expected:(Jet energy scale dominates!) Should do better!

51

Run 1 Searches for ttbar Resonances

Investigate models thatdynamically break EW

symmetry, such as topcolor-assisted technicolor

Search for narrow model-independent Xtt

resonances in l+jets

Exclude a narrow, leptophobicX boson with mX < 480 GeV/c2

Coming in Summer ‘05:Run 2 CDF Matrix Element

Analysis Xttbar

52

What Else is in the Top Sample?

Are some of the top-like events from SUSY or other new physics?

• We see what looks like top so far, but with more

statistics, we can probe kinematics and

properties further, to see if there are any non-SM

events

ttbb

WW++

Are top kinematics as we expect?

tt~

bb

53

Run 1: Anomalies in the Top Di-lepton Sample?

Four di-lepton candidates

with very high MET.

?

54

Run 2: Di-lepton Kinematics

Distributed as expected? More data to come…

55

Analysis of SM Agreement Probability Using Kinematics

Probability() of CDF outcome with SM hypothesis using 4 kinematic variables [MET, Tw, PT, (MET,l )]

= 1.6%

Topological weighting parameter (TW)

PT(l

ep

ton

)

56

Kinematic Discriminants Look Standard

Result driven by low pT excess. Consistent with SM hypothesis.More data will allow better sensitivity of such tests in the future.

MET

pT lepton T

57

CDF Top Physics PublicationsTop Pair Production Cross Section

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV using Dilepton Events Submitted 04/27/04, accepted August 2004 Phys. Rev. Lett. 93, 142001 (2004)

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV using Lepton + Jets Events with Secondary Vertex b-tagging Submitted 10/14/04, accepted March 2005 Phys. Rev. D71, 052003 (2005)

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV using Kinematic Fitting of b-tagged Lepton + Jet Events Submitted 09/09/04, accepted April 2005 Phys. Rev. D71, 072005 (2005)

Measurement of the ttbar Production Cross Section in ppbar Collisions using the Kinematics of Lepton+Jet Events Submitted 04/27/05 to Phys. Rev. D hep-ex/0504053

Measurement of the tt-bar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV Using Lepton Plus Jets Events with Semileptonic B Decays to Muons Submitted 06/01/05 to Phys. Rev. D hep-ex/0506001

Search for Single Top Production

Search for electroweak single top quark production in ppbar collisions at sqrt(s)=1.96 TeVSubmitted 10/20/04, accepted January 2005 ･Phys. Rev. D, 71 012005 (2005)

Top Properties

Search for Anomalous Kinematics in ttbar Dilepton Events at CDF II Submitted to Phys. Rev. Lett. 12/10/04, accepted June 2005. hep-ex/0412042

Measurement of B(t --> Wb)/B(t --> Wq) at the Collider Detector at FermilabSubmitted to Phys. Rev. Lett. 05/27/05 FERMILAB-PUB-05-219-E.

58

Near Term Plans

Summer conference results will include •new top mass measurement in the dilepton channel •matrix element analysis of X ttbar•Tau + jets ttbar cross section•Update on all hadronic cross section•Update on dilepton cross section…

CDF will shoot for presenting physics results on 1 fb-1 for Winter Conferences 2006!

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Summary Many more analyses are testing top properties, and hunting for hints of new physics in the top quark datasets:

•SecVtx and SLT combined tags in W+jets

•Top spin, top charge, top lifetime

•Ongoing search for single top in lepton + jets events

•Tests of consistency of kinematics with the SM in the top quark sample

•Rare top decays (tZc) and FCNCs

•Top production (q-qbar v. glue-glue)

60

Conclusions

As we increase our datasets at the Tevatron in Run 2, CDF will have much to say about the top quark, it’s

properties, and the possibility of new physics in our top quark samples.

Stay tuned: CDF top quark publications are rolling…

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Searches for Single Top

Combined Channel Search:

(s+t) < 13.7 pb @ 95% C.L.

t-Channel Search:

(t-chan) < 8.5 pb @ 95% C.L.

We are still looking for single top!

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top and W masses

constrain the mass of the

Standard Model Higgs

Standard Model Higgs?

LEP Direct Search Limit: Mass (Higgs) > ~114 GeV

(World Data 2 fit: MH ~ 96 GeV)

63

Can a t' Exist?•Z width measurement rules out a fourth generation with a light neutrino m()<m(Z)/2

•He/Polonsky/Su (hep-ph/0102144): a generic 4th chiral generation is consistent with EWK data; can accommodate a heavy Higgs (500 GeV) without any other new physics (similarly with 2HDM)

•Some Little Higgs theories predict a heavy top T at or below the TeV scale (reference)

•N=2 SUSY requires three more “mirror” generations – the SUSY breaking mechanism can induce couplings of the mirror quarks with the known ones

•Other models (eg: “Beautiful Mirrors” hep-ph/ 0109097) include possibilities of a new heavy up-type quark decaying to Wb

64

Neural Network Details Neural Network Training:Seven input variables

HT

AplanarityMaximum jet ET(Jets 3,4, and 5)

NN structureSeven input nodesOne hidden layer with seven nodesOne output node (signal target = 1, background = 0)Feed-forward network

Trained using Root_JetNet

pZ/ ET

Minimum dijet invariant mass Minimum dijet separation (R)