1. Recent Measurements of the Top Quark from Fermilab
Kevin Lannon
The Ohio State University
For the CDF and D0 Collaborations

2. Note to Slide Readers
This presentation makes heavy use of animations. Several slides to do make sense unless viewed in animated form. I recommend viewing this presentation as a slide show.
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3. The Top Quark and the Standard Model
Top quark needed to complete the “period table” of the Standard Model
Top quark discovery
Late 1970’s: Existence suggested by discovery of b quark
1980’s: Existence required for consistency of Standard Model
Eluded experimental observation for two decades
1995: Observed at Tevatron
Properties of top quark that made discovery difficult also make study interesting!
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4. Top Quark is Special Top is really massive
Comparable to gold nucleus!
In Standard Model: Mass related to coupling to Higgs (Yukawa coupling)
Top Yukawa coupling near unity (natural value?)
Why are couplings for other quarks so small in comparison?
Special relationship between top and Higgs?
Top quark decays very quickly (10-24 seconds)
Decays before hadronization
No hadron spectroscopy
Momentum and spin transferred to decay product u d s c b t
Quark Masses
GeV/c2
5 orders of magnitude
between quark masses!
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5. The Tevatron Accelerator
Highest energy accelerator in the world (Ecm = 1.96 TeV)
World record for hadron collider luminosity (Linst = 2.86E32 cm-2s-1)
Only accelerator currently making top quarks
Run I ( )
Integrated 105  4 pb-1 luminosity
Discovery of the top quark
Run II (2001-present)
Integrated > 2.5 fb-1 and counting!
Precision study of top quarks
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6. Today’s Presentation:
Tevatron Performance
Integrated Luminosity
Peak Luminosity
Today’s Presentation:
~1 fb-1
Analyzed by Summer
Integrated luminosity at CDF and D0
Total delivered: ~2.7 fb-1 to each experiment
Total recorded: ~2.2 fb-1 (~ 20 Run I!) at each experiment
So far for top analyses, used up to ~1 fb-1
More analyses with fb-1 in progress for summer
Doubling time currently ~1 year
Future: ~4 fb-1 by end of 2007, ~8 fb-1 by 2009
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7. CDF and D0 Detectors CDF D0
General purpose detectors capable of many different physics measurements
Top physics uses almost all detector systems
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8. Top Quark Production at Tevatron
QCD pair production
NLO = 6.7 pb
First observed at Tevatron in 1995
~85%
~15%
s-channel
t-channel
EWK single-top production
s-channel: NLO = 0.9 pb
t-channel: NLO = 2.0 pb
First evidence!
???
Other?:
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9. SM Top Quark Decays BR(tWb) ~ 100%
Particular analyses usually focus on one or two channels
New physics can impact different channels in different ways
Comparisons between channels important in searching for new physics
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10. Top Signatures Dilepton Lepton + Jets All Hadronic Electron or muon
Jet: shower of particles
b-jet: identified with secondary vertex tag
Neutrino: Missing ET
Dilepton
Lepton + Jets
All Hadronic
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11. Top Production Rates Like finding a needle in a haystack . . . .
Needle in haystack (approx.)
Efficient Trigger
~90% for high pT leptons
Targeted event selection
Distinctive final state
Heavy top mass
Advanced analysis techniques
Artificial Neural Networks
Like finding a needle in a haystack
One top pair each 1010 inelastic collisions at s = 1.96 TeV
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12. Top Quark Physics is Rich
Parallel Sessions
Systematically limited measurements
Cross section (~12% precision)
Mass (~1% precisions)
Statistically limited measurements
Most other measurements of top quark properties
Top quark charge
Top quark production mechanism
Searches
Single top production
Resonant production
Top to charged Higgs
J14, R14
J14, R14
C14, F1, X13
F1, J14, K14, R14, T14
K13, K14, J14
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13. Measuring the Top Cross Section
Agreement between theory and experimental important test of top quark properties (spin, couplings, mass)
Techniques form basis for top properties measurements
Key: separating top from backgrounds
Two main techniques:
Event Kinematics: central, spherical events with large transverse energy
HT  scalar sum of lepton, jet, and missing ET
Presence of b-jets: Detected through long life-time of the B hadrons. Decays at displaced vertex
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14. Recent Cross Section Results
L=900pb-1
Lepton + Jets
Individual Measurements approaching same precision as theoretical calculation
Session R14 (Monday)
Excess of events with  3 energetic jets +  1 b-tag
Dilepton Channel
L=900pb-1
Excess of events with  4 energetic jets and “top-like” kinematics (determined by a multivariate discriminant technique
Excess of events with
Two high pT leptons
Two energetic jets
Missing ET
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15. Several cross section talks in Session R14 (Monday)
Cross Section Summary
Several cross section talks in Session R14 (Monday)
Measurements in many different channels
Experimental precision approaching theoretical uncertainty (~12%)
Working on Tevatron combination
CDF Run II Preliminary
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16. Why Measure the Top Mass?
It’s the most striking feature of the top quark!
Consistency of mass and cross section  Standard Model Top?
Related to the Higgs mass through radiative corrections to the W mass
Provides indirect constraint on Higgs mass
More precision  Tighter constraint
Tevatron Run II goal
Uncertainty < 3 GeV/c2 with 2 fb-1 data
New Goal: Uncertainty ~ 1 GeV/c2 by end of Run II
MW  M2top
MW  ln MHiggs
Summer 2006
Updated Result in Next Talk
Already exceeded!
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17. Measuring the Top Mass is Challenging
What a theorist sees:
What an experimentalist sees:
Measure jets, not partons
Account for bias and resolution  Jet Energy Scale
Determine which jet should be assigned to which parton  Combinatorics (up to 720 permutations for all hadronic decay!)
Don’t measure neutrino momentum Infer pT indirectly
Extra jets from radiation confuse things
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18. Jet Energy Scale
Determine parton energy from measurements in calorimeter
Correct for
Detector effects
Fragmentation/Hadronization
Underlying event
Energy scale determined from data and MC
Uncertainties in jet energy scale directly affect top mass uncertainties
Leading uncertainty without special treatment!
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19. In-Situ Jet Energy Scale Calibration
W mass known very precisely from other measurements
Use W mass reconstructed from jets to constrain jet energy scale
Uncertainty decreases as data increases
Key reason why we’re doing better than originally projected!
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20. Results: Lepton + Jets Channel
170.9 ± 2.2 (stat+JES) ± 1.4 (syst) GeV/c2
World’s best
Advertise. Picked the top three results in combination.
Session T14 (Monday)
Both use
Matrix element technique
In-situ JES calibration
170.5 ± 2.4 (stat+JES) ± 1.2 (syst) GeV/c2
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21. Results: All-Hadronic
Session T14 (Monday)
171.1 ± 3.7 (stat+JES) ± 2.1 (syst) GeV/c2
Combines matrix element and template techniques
First incorporation of in-situ JES calibration in all-hadronic channel
This measurement more precise than expected based on past performance!
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22. Top mass measurements in
Tevatron Combination
Top mass measurements in
Sessions F1 (Saturday),
J14, K14 (Sunday),
and T14 (Monday)
Many more measurements than can be discussed here
Combine for better precision
Best individual measurement: 1.5%
Combination: 1.1% uncertainty!
See next talk for impact on indirect Higgs constraints
Add the weights! Projection
170.9 ± 1.1 (stat) ± 1.5 (syst) GeV/c2
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23. Top Charge Are we observing Standard Model top?
Standard Model top has charge +2/3
Alternative hypothesis: exotic quark with charge -4/3
Difficult to measure (“t”W+b or W-b)
W charge measured through the lepton (straightforward)
Bottom charge inferred from jet (difficult)
Correctly pair the lepton and b jet (difficult)
Bayes factor, “Like B physics”
Exclude top charge of -4/3 with 81% C.L.
Session K14 (Sunday)
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24. Top Production Mechanism
Session J14 (Sunday)
~85%
~15%
Does ratio of qq tt and gg tt match theoretical expectation?
Depends on top mass, pdfs, etc.
Could be modified by non-standard production
Exploit correlation between low pT track multiplicity and number of gluons
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25. The Search for Single Top
t-channel
s-channel
Standard Model
Rate  |Vtb|2
Spin polarization probes V-A structure
Background for other searches (Higgs)
Beyond the Standard Model
Sensitive to a 4th generation
Flavor changing neutral currents
Additional heavy charged bosons
W’ or H+
New physics can affect s-channel and t-channel differently
Tait, Yuan PRD63, (2001)
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26. Signal and Backgrounds
Single-top Signature
Other EWK tt
High pT e or 
: MET
Multi-jet QCD
W + Heavy Flavor
W + Light Flavor (Mistags)
2 High ET jets,  1 b-tagged
Must use multivariate, kinematic techniques to separate signal from background
Signal / Background ~ 1/20
Signal size ~ background uncertainty
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27. Multivariate Analysis Techniques
Combine information from several variables into a single, more powerful discriminant
Six separate analyses
Used many different multivariate analysis techniques: Decision tree, matrix element, multivariate likelihood, neural network
Only moderate correlations among discriminants  Can combine results for greater sensitivity
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28. Single Top Results 2.3! Session X13 (Tuesday) Session F1 (Saturday)
deficit
Normalized to fit
Matrix Element
Neural Network
Expected Signal Significance: 2.5
Expected Signal Significance: 2.6
2.3!
Session X13 (Tuesday)
Session F1 (Saturday)
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29. Single Top Results 3.4! 2.9! Session X13 (Tuesday)
Expected Signal Significance: 2.1
Expected Signal Significance: 1.8
3.4!
2.9!
Session X13 (Tuesday)
Session X13 (Tuesday)
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30. All Single Top Results D0 Combination: 3.5 Session X13 (Tuesday)
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31. 0.68 < |Vtb| < 1 at 95%CL (f1L = 1)
Limit on Vtb
(single top)  |Vtb|2
First direct limit on Vtb
No assumption about number of quark generations
Assuming Standard Model production:
Pure V-A and CP conserving interaction
|Vtd|2 + |Vts|2 << |Vtb|2  B(t Wb) ~ 100%
Bayesian limits with flat prior between 0 and 1
Session X13 (Tuesday)
0.68 < |Vtb| < 1 at 95%CL (f1L = 1)
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32. Summary
Many more top physics results available than could be covered here
See public webpages for CDF and D0:
Very exciting times in top physics at the Tevatron
Top mass uncertainty 1.1%!
First evidence for single top production: > 3!
Cross section: Uncertainty on measurements approaching theoretical uncertainties
Just beginning to gain sensitivity to many top quark properties
Great place to search for new physics!
Stayed tuned for new results this summer
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33. Backup Slides
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34. Weights in the Combination
CDF and D0 both crucial for best precision
Better than expected performance from all-hadronic measurement  In-situ JES calibration
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