1. 3rd Grenoble Top Workshop – October 25, 2008
Top Properties
at Tevatron
Run II
3rd Top
Workshop _
Charles Plager
UCLA
For the CDF and DØ Collaborations
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

2. New Era of Top Precision Physics!
CDF and DØ now have more than forty (40 !!!) times as much integrated luminosity as we did when we discovered the top quark in Run I!
With the data we have recorded, we are now able to have large, very pure top samples.
For example, of the almost 50 results that CDF sent to the winter conferences, more than half were in top physics!
Double B-Tag Lepton + Jets Candidates
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

3. A Quick Note About Scale at the Tevatron
Cross Sections at Ös = 1.96 TeV
For those not
intimately familiar
with Tevatron
high pT Physics:
Top:
1 in 10 Billion
Reducing and understanding
backgrounds is the key.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

4. 3rd Grenoble Top Workshop – October 25, 2008
Top Quark Review
Fundamental question:
Is it the truth, the Standard Model (SM) truth, and nothing but the truth?
Did we really find the top quark?
Is it the SM top quark?
Is it only the SM top quark?
The top quark is an ideal place to look for Beyond the Standard Model Physics! -
tt Pair Lepton + Jets Decay _
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

5. What Can We Study About Top Quarks?_
Branching ratios
Rare decays
Non-SM decays
Decay kinematics
W helicity
|Vtb|
Top physics
is very rich.
Production cross section
Production mechanism
Resonance production
Production kinematics
Spin polarization
Top charge
Top spin
Top mass
Top width
In today’s talk.
Public Tevatron analyses.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

6. 3rd Grenoble Top Workshop – October 25, 2008
Top Pair Decay Modes
According to the SM, top quarks almost (?) always decay to Wb.
When classifying the decay modes, we use the W decay modes:
Leptonic
Light leptons (e or )
Tauonic ()
Hadrons
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

7. Top Pair Cross Section Measurements
Why measure cross section?
Theory has precise estimate(s - see next slide).
New physics will affect different modes differently.
E.g., t ! H+ b, H+ !   decay is not equally well reconstructed in all decay modes.
Important to check assumptions and tools
With b tagging, using neural net, etc.
Need to understand sample composition for properties measurements.
Cross section formula:
Where:
- number of observed events, background estimate.
- geometric acceptance, reconstruction efficiencies (e.g., lepton ID, b-tagging), and relevant branching fractions (e.g., W decays).
- integrated luminosity.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

8. Theoretical Top Pair Cross Section
Easy Question: What is the theory cross section for top pair production at the Tevatron (√s = 1.96 TeV)?
Not-as-easy Answer: Depends on (in descending order of importance):
Top mass.
NLO vs NNLO parton distribution functions (PDF).
Who you ask.
NLO PDF and 175 GeV top mass: 6.7 pb.
World average top mass !172.5 GeV ) +0.5 to +0.6 pb.
NLO ! NNLO PDF: ) +0.2 to +0.3 pb.
Cacciari et al. ! Kidonakis and Vogt: ) +0.1 pb.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

9. Lepton + Jets ANN Cross Section
7 input variables.
Most sensitive variables:
∑ ET jets for ≥ 3rd jet
HT (scalar sum of ET)
Event selection:
≥ 3 jets
1 high pT electron or muon.
High missing ET (consistent with missing  from W decay).
No b tagging requirement.
S ET
||max HT
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

10. 3rd Grenoble Top Workshop – October 25, 2008
ANN Cross Section
Signal estimate from fit to Neural Network output.
Dominant systematic uncertainties:
QCD (multijet) modelling
Parton Shower model
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

11. Lepton +  Cross Section
Selection requires 1 , 1 light lepton, and two high pT jets
At least one jet identified b-tagged.
 selection
Three types:
1 track, no EM calorimeter clusters
 ! - t
1 track, with EM clusters
 ! - t + n 0
2 or more tracks
 ! - - + t + n 0
Neural net designed to select real  s.
One for each type
Variables:
 track quantities
Hadronic and EM calorimeter energies
Shower shapes
Separate NN trained to reject electrons for type 2  s.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

12. Lepton +  Kinematic Results
World’s
Best Lepton + 
Measurement!
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

13. Top Pair Production Mechanism
SM theory predicts 15% of top pair production from glue-glue annihilation.
How can we determine the fraction?
 between leptons in dilepton sample.
Event kinematics
e.g., cos (*), top quark speed ()
Use NN with lepton + jets sample
Track density of tracks not in jets.
Gluon jets have more associated tracks.
Use lepton + jets sample
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

14. Production Mechanism Results
Dilepton result:
Very statistics limited!
Lepton + jets combination
World’s
First Dilepton
Measurement!
World’s
Most Precise
Measurement!
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

15. W Helicity
Examines the nature of the tWb vertex, probing the structure of weak interactions at energy scales near the Electro-Weak Symmetry Breaking scale.
Stringent test of V-A interaction in SM. Standard Model expectations:
F0 = 0.7, F- = 0.3, and F+ = 0.0
V+A is Suppressed
in the SM
W- left-handed fraction F- = 0.3 t b W
+1/2
-1/2 +1
W+ right-handed fraction F+ = 0.0 t W b
+1/2 +1
-1/2 t
W0 longitudinal fraction F0 = 0.7 W
+1/2 b W
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

16. 3rd Grenoble Top Workshop – October 25, 2008
W Helicity
Uses both dilepton and lepton + jets channels.
Reconstruct cos (*) for leptonic W decays. Use:
Kinematic fitter (LJ)
Lepton pT (dilepton)
Use hadronic W decay as well. We do not know which jet is from up-type quark decay, but can reconstruct | cos (*) | .
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

17. 3rd Grenoble Top Workshop – October 25, 2008
W Helicity Results
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

18. 3rd Grenoble Top Workshop – October 25, 2008
W Helicity Results
Combines to CDF measurements, both using lepton + jets channel.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

19. Search for tt Resonances_
Search for tt Resonances
Uses lepton + jets
event selection:
High pT lepton
Missing transverse energy
B-tag.
Invariant mass
reconstruction:
Assume pT = MET
Solve for Pz assuming W mass.
Allows for events with less than three jets.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

20. Search for tt Resonances_
Search for tt Resonances
For Z’ limits, assuming a lepto-phobic Z’
Br (Z’ ! tt) = 100% _
World’s
Most Precise
Measurement!
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

21. Search for Invisible Top Decays
It is the relative reconstruction efficiency  acceptance that determines the relative yield.
is the relative acceptance when one top decays to the Wb while the other decays to the new decay, XY.
is the relative acceptance when both top quarks decays to the new decay, XY.
Compare expected yield to observed number of candidate events.
Create Feldman-Cousins acceptance bands using number of observed events.
t ! Zc, t ! gc, t ! c, t ! Invisible.
What do we mean by “invisible?”
Not (well) reconstructed as double b-tag lepton + jets.
What would happen if there were a large branching fraction to an invisible decay? For example,
Br (t ! Invisible) = 10%?
Br (t ! Wb) = 90%
P (tt ! Wb Wb) = 81%
) For a purely invisible decay, we should have an 19% deficit when we look at the L + J event yield for a given theoretical cross section. XY
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

22. Feldman-Cousins Acceptance Bands
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

23. Search for Invisible Top Decays
Theory cross section from Cacciari et al. (hep-ph: ) assuming CTEQ PDFs.
World’s First
Measurement!
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

24. Search for the Top FCNC Decay t → Zq
Top FCNC extremely rare in the SM: B(t → Zq) = O(10–14)
Beyond SM: B(t → Zq) up to O(10–4),
Any signal at Tevatron or LHC: New Physics.
Signature: tt → Wb Zq (Z + ≥4 Jet).
Dominant SM background: SM Z + Jets.
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

25. Search for t → Zq: Ingredients’
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

26. Search for t → Zq: Results
Analysis method:
Simultaneously fit mass 2 in 3 regions:
Signal (B-tagged and Anti b-Tagged)
Control
) Constrain shape & normalization of Z + jets background.
Data compatible with background only.
Feldman-Cousins limit with systematic uncertainties:
3.5 times better than best
published limit (L3).
World’s Best
Measurement!
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

27. 3rd Grenoble Top Workshop – October 25, 2008
Looking Forward
Top quark physics is becoming precision field.
Almost all analyses (except mass) are still statistics limited.
So far, most (but not all) things are frustratingly consistent with the SM.
CDF and DØ each have many of the world’s best measurments:
physics/new/top/top.html
WWW/results/top.htm
MZ’ (leptophobic) > 760 GeV (95% C.L.)
Br (t ! Zq) < 3.7% (95% C.L.)
Br (t ! Invisible) < 9% (95% C.L.)
fgg < 38% (95% C.L.) …
Lots of exciting top physics happening at the CDF and DØ.
CDF, DØ, and the Tevatron are all running very well.
A lot of room to grow.
2 fb-1
8 fb-1
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

28. New Era of Precision Top Physics!
2010 PDG Top Entry
2008 PDG Top Entry
2006 PDG Top Entry
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

29. Top Physics Finally Makes Prime Time
The Big Bang Theory!
Mondays at 7:00 on CBS.
Top Branching
Fractions
Top FCNC
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

30. 3rd Grenoble Top Workshop – October 25, 2008
Thank You!
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008

31. 3rd Grenoble Top Workshop – October 25, 2008
Backup Slides
Charles Plager
3rd Grenoble Top Workshop – October 25, 2008