1. The Top Quark at CDF Production & Decay Properties
Tony Liss
University of Illinois/CEA Saclay

2. Production at
The production is dominantly qq at the Tevatron (opposite at LHC)
State-of-the art theory calculations agree well with the latest measurements
Most recent combined s is with only part of the data. Individual measurements use more:
~85%
~15%

3. Production Cross Section Measurement
Event selection
High Pt electron or muon (l+j)
Second (OS) electron or muon or high-Pt track (ll)
Missing ET>20 GeV
Lepton+jets:
≥ 3 jets, |h|<2 w/at least 1 b-tag
b-tag with secondary vertex, NN or m in jet
Dileptons:
≥2 jets, |h|<2
These are the basic data selection of almost all of what follows…

4. Latest Measurements
Dilepton channel: Require 2 jets for S/B
Lepton+jets channel: b-tagging for S/B

5. Cross Section Systematics
ID & b-tagging efficiencies
Acceptance modeling (PDFs, JES)
Backgrounds
Non-W QCD
Tag rate for non-b jets (“fake tags”) (lepton+jets)
W+heavy flavor normalization
Integrated luminosity uncertainty

6. Production Cross-Section Summary
Dilepton measurements
Lepton+jets measurements
Sensitivity to tau decays
All jets
Combined ( 760pb-1 )
Band is theory for Mtop= 175 GeV/c2

7. Is it 85:15 qq:gg? cosθ* Production Mechanism Two CDF techniques:
NN based on different FS kinematics
Multiplicity of low-Pt tracks
W+ ≥4 jets
cosθ*

8. Production Mechanism/Low PT Multiplicity
Multiplicity distributions taken from W+0 jet (qqbar) and high ET dijet (gluon-rich) data – corrected for gg or qq content.
These are “extra” tracks: not part of a jet. Pt<3 GeV/c
Fit to the data:
Data-based templates:
Ntrk: s(ggtt)/s(qq tt)= 0.07±0.14±0.07

9. Production Mechanism/FS Kinematics
Spin correlations! Different for qq vs. gg: .
Like Spin
Unlike Spin
Spin correlations lead to different decay kinematics.
Use a NN with top velocity and production angle, 6 decay angles.
fgg < 0.33 (0.61) at 68% (95%) C.L.

10. Production Mechanism Systematics
Ntrk:
Track multiplicity modeling
<Ntrk> vs. Ng
Removal of tracks from jets
Choice of Jet Et threshold
FS Kin:
Reconstruction of final state
JES, ISR/FSR, PDFs
Both:
Background modeling

11. What is the charge of the top quark?
We assume this, but we have only recently measured it.
Step 1: Pair a b-tagged jet with W+ or W- side
l+j : Use the min c2 from the mass fitter (MT175 GeV/c2).
ll: Use Mlb2 – reject pairing that gives highest value.
Step 2: Measure the jet charge
Measured with data to give 61% correct sign of Q.

12. Top Charge Results
Measure the number of events with QW*Qb > or < 0 :
Write likelihood fcn., using purity of jetQ assignment, number of signal events and number of QWQb>0 and <0. Minimize –lnL:
Pseudo experiments with either SM or XM have distribution of max L like this:
f+= frac. Of Q=+2/3 tops
XM excluded at 87% C.L.

13. Top Charge Systematics
Purity of the JetQ
MC modeling
Pairing
ISR/FSR, PDF, JES
Mtop
Background modeling

14. What is the Lifetime of the Top Quark?
Technique #1: Direct measurement
Sensitivity to lifetime through d0 distribution of high-Pt lepton n
SM: t & W decay happen almost at the primary interaction vertex.
Long-lived top  broad impact parameter distribution.
Data distribution:
MC Templates:
-lnL template fit to data:
ct < % C.L.

15. What is the Lifetime of the Top Quark?
Technique #2: Indirect measure:
Sensitivity through top width in Mtop reco.
Templates:
Fits to data:

16. Top Lifetime Systematics
Direct:
Modeling of the background d0 shapes
Tagging efficiencies for backgrounds
Modeling of QCD background
Prompt resolution fcn.
Modeling of the signal d0 shape
Top decay kinematics
ISR/FSR, PDFs, JES
Indirect:
Reconstructed mass distribution modeling
MC modeling
Background shapes
Acceptance

17. Is the top decay V-A?  In the SM the V-A vertex gives
Where W0,W-,W+ are longitudinal, left, and right-handed W bosons.
For a massless b quark, G(W+)=0 .
The different W boson polarizations give different angular distributions for the decay leptons:
l + W+ b θ*
W boson rest frame 

18. W Helicity Measurement
The measurement uses l+j events.
Full reconstruction of the event is performed using the top-mass kinematic fitter (Mtop175 GeV/c2) to find the W rest frame.
Two types of fits are performed (both with f0+f++f-=1):
1D fits:
Fix fraction, f+, of right-handed W bosons=0
Fit the longitudinal and left-handed fractions f0 & f-.
2D fits:
Fit f0 & f+ simultaneously.

19. W Helicity Results 2D fit gives: F0= 0.61 ± 0.20 ± 0.03
F0 fit, F+0:
F+ fit, F00.7:
2D fit gives:
F0= 0.61 ± 0.20 ± 0.03
F+ = ± 0.08 ±

20. W Helicity Systematics
Shapes & Reconstructing the final state
Background shapes
ISR/FSR, PDFs, JES
MC modeling
Top mass

21. Charge Asymmetry in Top Production
Charge asymmetry in top production, defined as
Incoming parton rest-frame
Arises as a result of interference at NLO
But it’s a small effect… +
A>0 +
A<0

22. Measuring A Assuming CP conservation charge asymmetry  F/B asym:
But a is not experimentally accessible. We use as the sensitive variable:
The rapidity difference of the leptonically and hadronically decaying top quarks, signed by the charge of the lepton. (Related to cosa at L.O.)
Requires full-reconstruction of top 4-vectors, done with modified c2 fitter.

23. Charge Asymmetry Results
Check of background modeling with anti-b-tagged sample
Fit to the data in the signal sample: ≥4 jets, ≥1 b-tag
Afb=(28 ± 13 ± 5 ) %
SM: 4-6% at NLO

24. Charge Asymmetry Systematics
Background shapes
MC generator
JES, PDF, ISR/FSR
Charge mis-ID
Top mass

25. FCNC in top decays? BR ~ 10-14 in SM  Any observation is PBSM!
Search in Zee,mm + 4 or more jets
≥ 1 b-tag
No b-tags
Event selection is optimized for best expected limit
see nxt. pg.

26. FCNC Search
Dominant backgrounds are Z+4 jets, WW, WZ. Background suppression is achieved via a mass c2 variable:
Note: final state is neutrino-free.

27. FCNC in Top Decay - Results

28. MC modeling of b-tagging PDFs, JES, ISR/FSR BR(tZc) vs. BR(tZu) Mtop
FCNC Systematics
Z-boson helicity
MC modeling of b-tagging
PDFs, JES, ISR/FSR
BR(tZc) vs. BR(tZu)
Mtop

29. Summary
Measurements of top production and decay are starting to get interesting…
The understanding of the detector, built from >10 years of top physics is paying off. And we’ve only analyzed a fraction of the data
Not yet analyzed & more coming
Results in this talk
We have a tremendous advantage of rate at LHC, but understanding the data will take time…