1. Physics with Top Quarks
Prof. Robin Erbacher
University of California, Davis
Lepton-Photon 2007

2. Something about top history
Top Discovery!
Tevatron Run 1
1994-5
R. Erbacher - LP07

3. Top Rediscovered in Run 2
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4. Periodic Table of the Particles
5 orders of magnitude!
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5. New Physics?!?
Many top properties measurements just beginning to have sensitivity: lots about top still to understand!
R. Erbacher - LP07

6. Top physics is one of the more sexy things to study at the Tevatron…
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7. Top Event Decays Top Quark Production Top Properties W helicity (V-A)
Branching ratios
Top to charged higgs
Top sample (W+c)
FCNC
Top Quark Production
Mechanism
Top Pair Cross Section
Ewk Production (single top)
Forward-backward asymmetry
Resonances decaying to top
stop production
Top Properties
Top Mass
Top Quark Width
Charge of Top Quark
R. Erbacher - LP07

8. Events Characterized by W Decays
tWb ~ 100%
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9. Dilepton Decay Mode
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10. Lepton+Jets Decays
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11. All-Hadronic Decays
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12. - Muon + jets event with 2 tagged b-quark jets Jet 2 Jet 1 MIP signal
In calorimeter
Jet 2
secondary
vertex
interaction
point
Jet 1
secondary
vertex
interaction
point
Muon + jets event with
2 tagged b-quark jets
R. Erbacher - LP07

13. Strong Pair Production at the Tevatron
How is top produced?
~85%
Rarely!!
Strong Pair Production at the Tevatron
~15%
One top pair each 1010 inelastic collisions at s = 1.96 TeV
R. Erbacher - LP07

14. Electroweak Single Top Production New Resonance Production?
s-channel ~1 pb
t-channel ~2 pb
New
Resonance
Production?
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15. Fermilab, Chicago, IL U.S.A.
Fermilab Tevatron
Tevatron DØ
CDF
Chicago
Booster
Wrigley Field
p source
Main Injector
Fermilab, Chicago, IL U.S.A.
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16. General purpose detectors capable of many different physics measurements
Top physics uses almost all detector systems
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17. Top Quark Production Production mechanism Top pair cross section
EWK production (single top)
Forward-backward charge asymmetry
Resonances decaying to top
Search for stop production
R. Erbacher - LP07

18. Does t-tbar production match NLO prediction?
(ggtt)/(pptt) = 0.07 ± 0.16
(NLO: gluon~15%, quark~85%)
(neural net analysis: fg < 68% CL)
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19. (tt) = Luminosity *  Top Pair Production Cross Section: t-tbar!
Nevents - Nbackground
(tt) =
Luminosity * 
t-tbar!
Top Pair Production
Cross Section:
As QCD predicts?
Only SM top?
By heavy particles?
R. Erbacher - LP07

20. Event topology Discriminant: No b-jet Top pair tagging Requiring two
tt=8.1 ± 0.9(stat)± 0.5(sys) pb
Requiring two
identified b-jets:
Ultra pure top
pair sample
Lepton + Jets
Top pair
R. Erbacher - LP07
tt=8.2 ± 0.5(stat)± 0.9(sys) pb

21. Many new dilepton measurements!
Dilepton Selection
Cross Section (Mtop =175 GeV)
2 Tight Leptons (1.2 fb-1)
tt= 6.2 ± 1.1(stat)± 0.7 (sys) pb
Lepton+Track (1.1 fb-1)
tt= 8.3 ± 1.3(stat)± 0.9 (sys) pb
Lepton+Track+btag (1.0 fb-1)
tt= 10.1 ± 1.8(stat)± 1.3(sys) pb
2 Tight Leptons (1.0 fb-1)
tt= 6.8 ± 1.2(stat)± 0.9(sys) pb
2 T+ L+T+btag comb (1.0 fb-1)
tt= 6.0 ± 0.9(stat)± 0.8(sys) pb
Lepton+Tau+btag (1.0 fb-1)
tt= ± 1.9(stat)± 1.4 (sys) pb
Many new dilepton measurements!
Tau Lepton
channels
difficult!
Expected xs*BR = 0.12 from theory
*BR(ttl++2+2b) =
0.19±0.08(stat) ± 0.07(syst) pb !
R. Erbacher - LP07

22. background uncertainty!
Single Top Production:
Rate  |Vtb|2 in SM
Sensitive to H+, 4th gen,
W’, FCNC, …
Signature ~ SM Higgs
SM cross section ~3 pb
Wbb
Wcc Wc
non-W
Mistags tt
Z/Dib
Backgrounds!
Best channels S/B~1/20
Signal smaller than
background uncertainty!
1/2 SM cross section
Add tevatron xs plot w/ st normalized to one
R. Erbacher - LP07

23. multivariate techniques can coax signal out from large backgrounds
neural network
Boosted
decision
tree
multivariate techniques
can coax signal out
from large backgrounds
boosted decision trees, matrix
element reconstruction, bayesian
neural networks, likelihood discriminants
R. Erbacher - LP07

24. D0 Single top results D0 Results: Search for Single Top 3.4!
DØ Combination: 3.6
Boosted
decision trees
3.4!
Expected significance: 2.3
Taken from users meeting talk-- clean it up a bit.
Expected sensitivity: 2.1
First direct measurement of Vtb:
0.68 <|Vtb|< 95%CL or
|Vtb| = 1.3 ± 0.2
s+t= 4.9 ±1.4 pb
s= 1.0, t =4.0 pb
PRL (2007)
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25. Results for Single Top from CDF
New CDF Results: Search for Single Top
Observed p-value = 0.09% / 3.1
Expected p-value = 0.13% / 3.0
3.1 
Evidence
Came much earlier than predicted due to experimental creativity and hard work.
LF:
Observed p-value = 0.31% / 2.7
Expected p-value = 0.20% / 2.9
Upper limit: 5.14 pb at 95% CL (Bayesian calculation).
Median expected limit in background-only pseudoexperiments:
2.06 pb
Matrix element:
Observed p-value = 0.09% / 3.1
Expected p-value = 0.13% / 3.0
s+t= 2.7 ± 1.2 pb
s= 1.1, t =1.3 pb
s+t= 3.0 ± 1.2 pb
s= 1.1, t =1.9 pb
Expected sensitivity: 2.9
Observed significance: 2.7
Expected sensitivity: 3.0
R. Erbacher - LP07

26. |Vtb|= 1.02 ± 0.18 (expt) ± 0.07 (theory)
Using the Matrix Element cross section measurement, CDF determines |Vtb| assuming |Vtb| >> |Vts|, |Vtd|
CDF Run II Preliminary L=1.5 fb-1
t-channel
s-channel
|Vtb|= 1.02 ± 0.18 (expt) ± 0.07 (theory)
Z. Sullivan, Phys.Rev. D70 (2004)
D0 |Vtb|>0.68, |Vtb| = 1.3 ±0.2
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27. Forward-Backward Production Asymmetry
Forward-Backward Production Asymmetry Afb
Forward-Backward Production Asymmetry
No asymmetry expected at LO
4-6% expected at NLO in parton frame
J. Kuhn, et al.
No asymmetry for gg initial states. Qq states with the same final state interfere due to different C eigenstates
Reduced asymmetry for tt+jets. Can only see this at the Tevatron?
Diagram interferences for qq
Smaller asymmetry in lab frame
R. Erbacher - LP07
Reduced Asymmetry in tt+jet -- Uwer, et al.

28. (Uncorrected for reconstruction)
First Afb Result from D0
Afb
< 0
> 0
How would new physics look?
F: fraction of top pair events
produced via Z' resonance
Replace a Z’ for the gluon in the diagram
For MZ' = 750 GeV:
F < 0.44 (expected)
F < 0.81 (observed)
Afb= 12 ± 8(stat) ± 1(syst) %
(Uncorrected for reconstruction)
R. Erbacher - LP07

29. Afb CDF First Afb Results from CDF Afb=(28 ± 13(stat) ± 5(syst) ) %
NLO: (4-7%) in y*Ql
Compare with D0 result:
Afb(bkg sub)=(14.4 ± 6.7(stat) ) %
Numbers of events measured in two bins: positive and negative values of y.Ql
The asymmetry value is background subtracted and corrected for smearing effects of ttbar pair reconstruction with the inversion of 2x2 matrix
Afb=(28 ± 13(stat) ± 5(syst) ) %
(Fully corrected)
R. Erbacher - LP07

30. Resonances decaying to ttbar
New
Resonance
Production?
New D0 Result!
See Talk by K. Tollefson Today:
Tevatron Striking Results
Bump-hunting for Xttbar!
R. Erbacher - LP07

31. (Limits on BR v. stop mass)
Can SUSY
stop hide alongside
top?
Stop Search
Single-variable separation poor;
Construct multivariate discriminant.
No evidence for stop
(Limits on BR v. stop mass)
R. Erbacher - LP07

32. Top Properties Top Mass Top Quark Width Charge of Top Quark
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33. Top Quark Mass: Important EWK Parameter
Key role in BSM physics models
Constrains the Higgs mass
Heavy: Unexpected role in EWSB?
Challenges: combinatorics, b-tagging efficiencies, jet energy scale.
Solutions: sophisticated analyses,
in-situ Wjj calibration
What a theorist sees…
R. Erbacher - LP07
What an experimentalist sees

34. Top mass: Exciting Program
of measurements
at the Tevatron
New for summer 2007!
New for summer 2007!
(not included in
March combination)
Most precise!
R. Erbacher - LP07

35. Top mass dilepton Many new top dilepton mass results!
Combining channels helps:
D0 matrix weighting + D0
neutrino weighting  ~4%
better for same luminosity
Matrix Element Weighting
Neutrino-weighting
Lepton Pt
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36. New Ideas New Ideas! Top mass with cross
section constraint: trades stat uncertainty for theory
LEPTON+JETS
DILEPTON
dilepton
Top mass extracted from cross sections: Compare to theory and across channels! Consistent with kinematic measurement?
Cross section constraint gains you precision in stat at the expense of theory. You gain only until stat~sys
NLO QCD calcs including higher order resummations. (Put the mass dependence in here?)
Cacciari, Mangano, et al
hep-ph/
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37. Top mass Best per channel
Mtop=171.6 ± 2.0 GeV/c2
Snapshot:
most precise
per channel
Top mass Best per channel
Most precise!
all-hadronic from
winter 2007:
Mt=170.4 ± 3.7(stat+JES) ± 2.1(sys)GeV/c2
Mt=170.4 ± 3.1(stat) ± 3.0(sys)GeV/c2
R. Erbacher - LP07

38. Top mass summary and combination
World Average March 2007:
Top mass summary and combination
Mtop=170.9 ± 1.9 GeV/c2
See P. Petroff’s Talk (next)
for electroweak implications
Note that no new averages will be made until CDF/D0 systematics effort is finished with some studies
D0-CDF Joint Systematics Effort Underway!
New combinations will follow…
R. Erbacher - LP07

39. Top Top quark width Quark Width t < 12.7 @ 95% CL Mt = 175 GeV
< Mtop=170
Blessed July 26th! First direct measurement of top width in run 2! (Lifetime limit with 300 pb-1 from CDF set indirect measurement)
R. Erbacher - LP07

40. Exclude top charge exotic
Top Quark Charge: +2/3?
Top Quark Charge: -2/3?
f+ = 0.87
P-value = 0.31
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)
Select and fully reconstruct top events in lepton+jets (2 b-tagged jets) and dilepton channel (≥1 tagged jet)
Determine:
flavor of b-jet
charge of W (lepton)
pairing between W and b (2 fit and Mlb)
D0 result with 300 pb-1:
See no evidence for exotic
model so far…
Exclude top charge exotic
model XM of -4/3* with 87% C.L.
*Chang,Chang,Ma ‘99
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41. Toplight charged higgs
Top Event Decays
W helicity (V-A)
Toplight charged higgs
Branching Ratios
Top sample (W+c)
FCNC
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42. t-W-b Coupling t-W-b Coupling V-A? The V-A character of the decay
makes the helicity of the W only
F0 = 0.70, F- = 0.30, F+ = 0
(longitudinal, left-handed, right-handed)
cos* = angle between lepton and top in W rest frame
R. Erbacher - LP07

43. t-W-b Coupling: W Helicity
1-d fit: Fix F0=0.7, fit for F+
D0(1 fb-1) : f+=0.02 ± 0.05 ± 0.05
95%CL
CDF1(1.7 fb-1) : f+=0.01 ± 0.05 ± 0.03
95%CL
CDF2(1.7 fb-1) : f+=-0.04 ± 0.04 ± 0.03
95%CL
2-d fit: Fit for F0, F+ together
CDF1(1.7 fb-1) : f0=0.38 ± 0.22 ± 0.07
f+=0.15 ± 0.10 ± 0.04
CDF2(1.7 fb-1) : f0=0.61 ± 0.20 ± 0.03
f+=-0.02 ± 0.08 ± 0.03
1.7 fb-1
V-A: F0=0.7, F-=0.3
V+A: F0=0.7, F+=0.3
R. Erbacher - LP07

44. Simultaneous measurement of  and Branching Ratio
New measurement by D0!
See Talk by K. Tollefson Today:
Tevatron Striking Results
one analysis is performing the simultaneous xs and R measurement. From that we extract V_tb. Let me call this R=R_b since it's the top decay Br into a b-quark over the top decay Br into all quarks. It is thus a measurement which is sensitive on b disappearance.
+0.87
tt = (stat+syst) ± 0.49 (lumi) pb
+0.094
R= (stat+syst)
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45. Limits on charged higgs
Ratio of Cross Sections:
Limit on Charged Higgs!
Limits on charged higgs
R=(pptt)l+jets/(pptt)ll
R=1.21 ± 0.26 (stat+sys)
Assume tH+b, H+cs only.
If MH=MW (not ruled out by LEP):
If you get questions about our assumptions on the charged Higgs model:a charged Higgs at 80 GeV which decays predominantly hadronically could be realised in the following scenarios:- general multi-Higgs-doublet model (MHDM).
It was demonstrated that such a leptophobic charged Higgs boson with a mass of 80 GeV could lead to noticable effects at the Tevatron if tanbeta < within MSSM:
large radiative corrections from SUSY-breaking effects can lead to a suppression of Hｱ -> tau nu compared to Hｱ -> cs.
Ah maybe interesting as well: LEP was not sensitive to a 80 GeV charged Higgs because it was in the W mass peak. CL
Expected: CL
Previous CDF result with 200 pb-1 explores other parameter spaces.
R. Erbacher - LP07

46. First: W+c Cross Section
Algorithm
Use soft lepton tagger (h.f. jets)
Wc: TL, SLT charges are fully anti-correlated,
large charge asymmetry A
Backgrounds: W+l.f., nonW QCD, DY, etc
mostly charge symmetric except DY
Observable: same sign subtracted events
N(OS) – N(SS)
g+s : ~ 90%, g+d: 10%
No direct measurement before, reduce systematic uncertainties on many other measurements, probe s-quark PDF and determine Vsc
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47. Search for tZc: FCNC Search for tZc: FCNC
Tree level FCNC
No FCNCs in SM at tree level
Allowed in higher order penguins
Light quark penguins observed
e.g. b→sγ observed by CLEO in 1995, BR O(10-4)
Not yet observed for top
SM BR: O(10-12)
New Physics models predict BRs up to O(10-2)
SUSY, Higgs doublet, Warped extra dimensions (J. A. Aguilar-Saavedra, Acta Phys. Polon. B35 (2004) 2695)
CDF: First Run 2 limits, better than LEP!
See Talk by K. Tollefson Today:
Tevatron Striking Results
Penguin
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48. Summary Summary The top quark is the least known quark,
and the most interesting for new physics.
The top physics program is very active
at the Tevatron, with both precision
measurements and first results appearing all the time.
Beginning to have sensitivity to the
unexpected in particle properties and in
the data samples!
R. Erbacher - LP07

49. Conclusions
Conclusions
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50. Backups
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51. D0 single top expected and observed
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52. How to extract top width
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53. Afb and higher orders
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54. CDF Single Top: What Changed ?
Likelihood
improved treatment of kinematic ambiguities
Bug fix in matrix element
More MC statistic allows refined training
Overall expected sensitivity gain:
(as measured on 955 pb-1 analysis) :35%
Matrix Element
Separate treatment of single and double tag events
More refined transfer functions
Overall expected sensitivity gain:
(as measured on 955 pb-1 analysis) :~10%
Common Improvements
new ALPGEN Monte Carlo
W + Heavy Flavor normalization from W + 1 jet eve nts
Define event selection on hadron level jets:
CDF Top group wide change
More meaningful to theorists
Better understood (MET resolution, nonW model..)
Causes event migrations:
LF loses 1 gains 7
ME loses 5 gains 4
for highest discriminant region
R. Erbacher - LP07

55. Event Yield of DPF and LP Analyses
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56. W + Heavy Flavor Estimate
Method inherited from CDF Run I (G. Unal et. al.)
Measure fraction of W+jets events with heavy flavor (b,c) in Monte Carlo
Normalize fractions to W+jets events found in data
New improvement: get normalization from W + 1 jet bin (instead of generic dijet sample)
Note: Similar for W+charm background
Correct data for non W+jets events
Heavy flavor fractions
and b-tagging efficiencies
from LO ALPGEN Monte Carlo
Calibrate ALPGEN heavy flavor
Fractions from W + 1 jet bin
Large uncertainties from Monte Carlo estimate and heavy flavor calibration (~25-30%)
CDF Run II Reference for standard method:
PhysRevD.71,052003
R. Erbacher - LP07

57. Heavy Flavor Normalization
Improve heavy flavor estimate by calibrating it in W+1 jet side band
Take advantage of NN based flavor separator
Compare Loose Secondary Vertex mass and NN flavor separator output:
consistent results within errors
K-factor for heavy flavor:
1.4 ± 0.4
Applied to predict W + Heavy Flavor content of W + 2 jets bin
mistags / charm ………. beauty
R. Erbacher - LP07

58. Q*h and Mlnb cross-checks
EPD > 0.9
EPD > 0.9
EPD > 0.966
EPD > 0.966
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59. Sensitivity to New Physics and WH
Single top rate can be altered due to the presence of New Physics:
t-channel signature: Flavor changing neutral currents (t-Z/γ/g-c couplings)
- s-channel signature: Heavy W boson, charged Higgs H+, Kaluza Klein excited WKK Z c t
W,H+
s (pb)
1.25 t (pb)
s-channel single top has the same final state
as WHlbb
=> benchmark for WH search!
Tait, Yuan PRD63, (2001)
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60. Single Top Candidate Event
t-channel single top production has a kinematic peculiarity:
Distinct asymmetry in Q x  distribution: lepton charge (Q) x pseudo-rapidity =-log (tan/2) of untagged jet
EPD > 0.9
Jet1
Jet2
Lepton
Run: , Event:
Central Electron Candidate
Charge: -1, Eta= MET=41.6 GeV
Jet1: Et=46.7 GeV Eta= b-tag=1
Jet2: Et=16.6 GeV Eta= b-tag=0
QxEta = 2.9 (t-channel signature)
EPD=0.95
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61. The Likelihood 2D Fit Best-Fit Point: Each nuisance parameter
fit for at each test value
of the cross section.
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62. Cos(theta*) kinematics
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