1. An Important thing to know.
The Top Quark
The Top Quark Mass
An Important thing to know.
11/24/2018
B. Todd Huffman - Oxford

2. t Z W b c s d u   e   e The Top Quark The Standard Model
The top quark was discovered only 10 years ago
Existence is required by the SM, but striking characteristics: its mass is surprisingly large
Studied only at the Tevatron
The Standard Model
Particle Masses
t Z W b c s d u   e   e
11/24/2018
B. Todd Huffman - Oxford

3. Why measure the Top Quark Mass?
Related to standard model observables and parameters through loop diagrams
Consistency checks of SM parameters
Precision measurements of the Mtop (and MW) allow prediction of the MHiggs
Constraint on Higgs mass can point to physics beyond the standard model
Summer 2005
11/24/2018
B. Todd Huffman - Oxford

4. Final State from Leading Order Diagram
Dilepton Channel
Final State from Leading Order Diagram
What we measure
Branching fraction: 5% (lepton = e or )
Final state: 2 leptons, 2 b quarks, 2 neutrinos
Combinatorial background: 2 combinations
2 neutrinos: under constrained, kinematically complicated to solve Mtop
S:B = 2:1 and 20:1 requiring 1 identified b tag
11/24/2018
B. Todd Huffman - Oxford

5. Final State from Leading Order Diagram
Lepton+Jets Channel
Final State from Leading Order Diagram
What we measure
Branching fraction: 30% (lepton = e or )
S:B = 1:4 to 11:1 depending on the b-tagging requirement
Combinatorial background: 12 (0 b tag), 6 (1 b tag), and 2 (2 b tags)
1 neutrino: over constrained
Most precise Mtop measurements
11/24/2018
B. Todd Huffman - Oxford

6. Final State from Leading Order Diagram
All Jets Channel
Final State from Leading Order Diagram
What we measure
Branching fraction: 44%
Huge amount of background S:B = 1:8 after requiring at least 1 b-tag jet
Combinatorial background: 90 combinations
Backgrounds mainly from multi-jet QCD production
11/24/2018
B. Todd Huffman - Oxford

7. Robust program of top quark mass measurements
Top Quark Mass at CDF
Robust program of top quark mass measurements
Many measurements in all the different channels -> consistency
Different methods of extraction with different sensitivity -> confidence
Combine all channels and all methods -> precision
11/24/2018
B. Todd Huffman - Oxford

8. CDF Measurement (~350pb-1)
Mtop
Different statistical and systematical sensitivities in each channel
Other sources arise from the assumptions employed to infer Mtop:
Initial state and final state radiation
Parton distribution functions
b-jet energy scale
Generators
Background modeling and composition
b-tagging efficiency
MC statistics
Systematics dominated by the uncertainty on parton energies (Jet Energy Scale, JES)
CDF Measurement (~350pb-1)
Statistical (GeV/c2)
Jet En. Scale (GeV/c2)
Other syst.
(GeV/c2)
Dilepton 6 3 2
Lepton+Jets 4 1
All Jets 5
11/24/2018
B. Todd Huffman - Oxford

9. Jet Energy Scale Jet energy scale
Determine the energy of the quarks produced in the hard scattered
We use the Monte Carlo and data to derive the jet energy scale
Jet energy scale uncertainties
Differences between data and Monte Carlo from all these effects
11/24/2018
B. Todd Huffman - Oxford

10. In-situ Measurement of JES
Additionally, we use Wjj mass resonance (Mjj) to measure the jet energy scale (JES) uncertainty
Constrain the invariant mass of the non-b-tagged jets to be 80.4 GeV/c2
Mjj
Measurement of JES scales directly with statistics!
11/24/2018
B. Todd Huffman - Oxford

11. Data and Monte Carlo W-jet pT b-jet pT ttbar pT Mttbar
Ask Lucio about this set of plots.
ttbar pT
Mttbar
11/24/2018
B. Todd Huffman - Oxford

12. In this Talk Lepton + jets: Template analysis
Lepton + jets: Matrix Element
Lepton + jets: Decay Length
All Hadronic: Ideogram
Missing Di-leptons…cannot go into detail on everything!
11/24/2018
B. Todd Huffman - Oxford

13. Mtop Lepton+Jets Results

14. Detected Top Candidate
Silicon Detector
Results
11/24/2018
B. Todd Huffman - Oxford

15. Top Mass - Guessing Jets
What you get if you always guess correctly, vs just trying all possible combinations. You cannot ‘pick the best one’….since you do not know the mass which one is ‘best’??
11/24/2018
B. Todd Huffman - Oxford

16. Run Monte carlo with various mass hypotheses.
Top Mass - Templates
Run Monte carlo with various mass hypotheses.
These are used as
‘templates’ that can be compared to data using the c2 difference between data and the template.
11/24/2018
B. Todd Huffman - Oxford

17. Top Mass – Background Templates
Use W+Jet background with fake electron and mistagged b to check that jet shapes are OK in MC.
Then use MC to generate a ‘background’ mass plot.
11/24/2018
B. Todd Huffman - Oxford

18. Template Analysis
Reconstructed mtop and mjj from data are compared to templates of various true Mtop and JES (jet energy uncertainty shift) using an unbinned likelihood
Uses all four samples to increase sensitivity
2 b tags
1 b tag (T)
1 b tag (L)
0 b tag
Expected S:B
10:1
4:1
1:1
0.6:1
Expected Number of Events ( tt = 6.1pb) 47
104 64
no a priori estimate
Data (680 pb-1) 57
120 75
108
11/24/2018
B. Todd Huffman - Oxford

19. Template Analysis Results
Using 360 candidate events in 680 pb-1 we measure
Using in-situ JES calibration results in 40% improvement on JES
Better sensitivity than the previous world average!
11/24/2018
B. Todd Huffman - Oxford

20. Matrix Element Analysis Technique
Optimizes the use of kinematic and dynamic information
Build a probability for a signal and background hypothesis
Likelihood simultaneously determines Mtop, JES, and signal fraction, Cs:
11/24/2018
B. Todd Huffman - Oxford

21. Matrix Element Analysis Technique
For a set of set measured variables x:
JES sensitivity comes from W resonance –this too is in the fit.
All permutations and neutrino solutions are taken into account
Lepton momenta and all angles are considered well measured
Background probability is similar, no dependence on Mtop
W(x,y) is the probability that a parton level set of variables y will be measured as a set of variables x (parton level corrections)
dn is the differential cross section: LO Matrix element
f(q) is the probability distribution than a parton will have a momentum q
11/24/2018
B. Todd Huffman - Oxford

22. Cross-check Monte Carlo with Data
Compare Data and Monte Carlo calculating the invariant mass of 2 and 3 jets
Signal probability evaluated at Mtop=174.5 GeV/c2 and JES=1 and using the most probable configuration
Excellent agreement found between data and Monte Carlo
11/24/2018
B. Todd Huffman - Oxford

23. Better sensitivity than the previous world average!
Results
Using the 118 candidates in 680 pb-1 our Mtop is:
with JES =  (stat)
Better sensitivity than the previous world average!
11/24/2018
B. Todd Huffman - Oxford

24. New technique – B Decay Length
The method has been published by C. Hill et al. at PRD 71,
B hadron decay length  b-jet boost  Mtop
Uses the average transverse decay length of the b-hadrons <Lxy>
Relies on tracking, no JES and uncorrelated with other measurements
11/24/2018
B. Todd Huffman - Oxford

25. Mtop All Jets Results

26. All Jets Main challenges in this channel: Selection and events
Small signal fraction S:B = 1:8 after requiring at least 1 identified b-jet
Large combinatorial background: 90 combinations
Selection and events
ET/  ( ET) < 3 (GeV)1/2
ET  280 GeV
nb-tag  1
Exactly 6 jets
Ideogram method from the Delphi experiment for the W mass measurement, used in a Run II preliminary D0 for top mass measurement in lepton+jets channel
Expected
Events (310 pb-1)
Multi-jets (light)
182
Multi-jets (heavy flavor) 68
Total background
240
tt (6.1 pb) 40
Data
290
11/24/2018
B. Todd Huffman - Oxford

27. Ideogram Overview Define a 2D event likelihood as
Weight each combination with kinematical and b-tagging information: wi
Extract from kinematical fit to mtop and manti-top  m1, m2, 1,2, 2
Sm calculated convoluting Briet-Wigners and Gaussian resolution functions
Scomb combinatorial background from Monte Carlo
11/24/2018
B. Todd Huffman - Oxford

28. Template Shapes Using the two fitted masses gives a good separation
Template for combinatorial background
Template for background
Signal, correct combination
Using the two fitted masses
gives a good separation
between
signal and background
11/24/2018
B. Todd Huffman - Oxford

29. Similar statistical sensitivity as the lepton + jets channel
Results
Using 310 pb-1 and 290 candidates we measure
First Tevatron Run II all jets Mtop measurement
Systematically limited!
Similar statistical sensitivity as the lepton + jets channel
11/24/2018
B. Todd Huffman - Oxford

30. Summary of Mtop Results
CDF Measurement
Extracted value (GeV/c2)
Statistical (GeV/c2)
JES (GeV/c2)
Other syst (GeV/c2)
Lepton+Jets: Template (680pb-1)
173.4
1.7
1.8
1.3
Lepton+Jets: ME(680pb-1)
174.1
2.0
1.5
Lepton+Jets: Decay Length (750pb-1)
183.9
+15.7
-13.9
0.3
5.6
Dilepton: Matrix Element (750pb-1)
164.5
4.5
2.6
All Jets:
Ideogram (310pb-1)
177.1
4.7
4.3
1.9
We compare (confidence and consistency) and combine (precision)
11/24/2018
B. Todd Huffman - Oxford

31. Combining Mtop Results
Excellent results in each channel
Combine them to improve precision
Include Run-I results
Account for correlations
Use BLUE (NIM A , A )
Matrix Element analysis in lepton+jets not yet included. Working to understand statistical correlations with Template analysis
2.6
CDF April’06
(750 pb-1)
11/24/2018
B. Todd Huffman - Oxford

32. Future We surpassed our Run II goal of measuring to 3 GeV/c2 precision
Have made extrapolations based on present methods
Upper limit: Only (stat) improves with luminosity
Lower limit: Everything improves with luminosity
Reality: likely somewhere in between
With full Run-II dataset CDF should measure Mtop to < 1%
11/24/2018
B. Todd Huffman - Oxford

33. Conclusions What has been shown.
First Run-II determination in all-jets channel
Multiple methods and channels
Observed consistency builds confidence
CDF combined
CDF should reach 1% precision with full Run-II data set
Tevatron combination better still
11/24/2018
B. Todd Huffman - Oxford

34. Conclusions
Present uncertainties on Mtop and MW help constrain MHiggs to about 40% MHiggs/ MHiggs
Best fit favors light MHiggs
where CDF/D0 are sensitive
where difficult for LHC
Mtop will continue to shrink
New CDF/D0 MW expected soon...
MW will also shrink
We'll continue to squeeze SM, will it hold?
11/24/2018
B. Todd Huffman - Oxford