1. Top Physics from the Tevatron to the LHC
Methods for top properties and charge measurements at D Christophe Clément (University of Stockholm)
Workshop on Top Physics:
from the Tevatron to the LHC
Grenoble – LPSC – October 2007
C.Clement
Top Physics from the Tevatron to the LHC

2. Top Physics: from the Tevatron to LHC
B(t→Wb)/B(t→Wq)
B(t→Wb)=1 assumed by
CDF and D cross section, mass, and property analyses
 Needs experimental validation
B(t→Wb) might deviate from unity:
Additional quark singlets or doublets
”Pollution” of top sample by non-top process!
Non-SM processes in the production
Non-SM in the decay (H+,...)
Experimentally B(t→Wb) affects number of b-jets  need to experimentally discriminate b/w t→Wb and t→Wqlight  b-tagging
3 quark generations + direct measurements
of Vub and Vcb predict Vtb,~1  B(t→Wb)~1
Update CKM with latest PDG ...
C.Clement
Top Physics: from the Tevatron to LHC 2

3. Deriving B(t→Wb)/B(t→Wq) experimentally....
Missing
transverse
energy t W
One high pT
isolated lepton
Select a top-enriched sample
e+jets and +jets channel
larges statistics, good S/B
# events with 0, 1 and ≥2 b-jets
B(t→Wb)
b-tagging efficiency
Jet identification efficiency
Probability to tag background
Statistics in the double tag sample crucial
b-jets?
light jets?
Show some plots of sample composition from the pusblished paper
light, c-jets
C.Clement
Top Physics: from the Tevatron to LHC 3

4. Lepton + jets sample composition
1) Slice the data: e / µ
3,  4 jets
0,1,  2 tags
2) Predict tt signal and background in each slice
e + 3 jets
0 b-tags
e +  4 jets
1 b-tags
 2 b-tags
µ + 3 jets
0 b-tags
µ +  4 jets
1 b-tags
 2 b-tags
B(t→Wb),
b-tagging probability
Show some plots of sample composition from the pusblished paper tt -
Jet multiplicity in events
Jet reconstruction efficiency, energy scale
Jet identification selections
C.Clement
Top Physics: from the Tevatron to LHC 4

5. Backgrounds in Lepton + jets samplett - .
W+jets
Z+jets
WW, WZ, ZZ
single top
multijet
True isolated
lepton processes
Ntrue
fake isolated
lepton processes
Nfake
Fake isolated electron
Jets with leading /πo , convertions, γwith random tracks,...
Fake isolated 
inside jets from heavy flavor or
in flight decays
Give more info on the matrix method?
Determine Ntrue , Nfake on a statistical basis
Two lepton ID criteria
loose ⊃ tight lepton
P(tight | loose) for fake and true leptons
C.Clement
Top Physics: from the Tevatron to LHC 5

6. Lepton + jets sample compositiontt - .
W+jets
Z+jets
WW, WZ, ZZ
single top
multijet
Small
derived from MC
Lepton, jet efficiencies
calibrated on data
σfrom data or NLO
Nother
Ntrue
Nfake
Nbefore tag = Ntt NWj Nfake Nother
Nn-tags = Pntt (B(t→Wb)) Nntt + PnWj Nnwj + N’nfake + Pnother Nnother
n-tags = 0, 1, 2 A
Tagging probability
Fit B(t→Wb), Ntt, Nwj to the Nn-tags
C.Clement
Top Physics: from the Tevatron to LHC 6

7. Top Physics: from the Tevatron to LHC
Pntt versus B(t→Wb)
For b-tagging in D see earlier
talk by Gordon Watts tt -
Probability to see n-tags in events (Pntt ) depends on the # of b-jets
Pn tt = R2 Pn tag(tt→bb) + 2 R(1-R)Pn tag(tt→bql) + (1-R)2Pn tag(tt→qlql)
tt event tagging
probability
2005
Secondary vertex tagging
0.9 fb-1
C.Clement
Top Physics: from the Tevatron to LHC
neural network tagging 7

8. Top Physics: from the Tevatron to LHC
0.9 fb-1
tricky piece:
flavor composition
of W+backround
exp [ ̶ (Ntt + Nbkg)] (Ntt + Nbkg)Nobs
P(Nobs|prediction)=
Nobs!
Ntt + Nbkg prediction
Nobs observation
1 tag bin:
Nbkg~15
Ntt ~55
small ΔNtt/ Ntt  large variation of P
0 tag bin:
Nbkg~170
Ntt ~30
small ΔNtt/ Ntt  small variation of P
C.Clement
Top Physics: from the Tevatron to LHC 8

9. Likelihood discriminant in 0-tag sample
To make full use of 0-tag sample need an additional constraint on in 0-tag sample
eg: discriminating variables used in the e+jet channel
1. Aplanarity
A = 3λ3/2 , λ3 smallest eigenvalue
of momentum tensor M
2. CM = 3(λ1λ2+ λ1λ3+ λ2λ3), λ are
eigenvalues of momentum M
3. DM = 27 λ1λ2λ3
4. Leading jet pT
0.9 fb-1
Jungle of topological variables:
Must be discriminating
Well modelled by Monte Carlo (validate description in control region)
Minimize systematic error (eg. some σtt analysis don't use HT because correlation with jet energy scale)
C.Clement
Top Physics: from the Tevatron to LHC 9

10. Data and prediction for 8.1pb and R=1
0.9 fb-1
e + ≥4 jets
0 tag
µ + ≥4 jets
0 tag
Nevents
C.Clement
Data and prediction for 8.1pb and R=1
Top Physics: from the Tevatron to LHC 10 10

11. Systematics on template shapes
illustration from 0.23 fb-1 Dataset
Some systematic uncertainties can affect the template shapes...
Systematics on template
shapes on tt→ l+jet
Jet energy scale
Jet identification efficiency
True jet energy resolution
W-modeling (W+jets)
Taggability
Tagging probabilities for b, c
and light jets
Example of systematics on tt templates
Illustrated with old 0.23 fb-1 analysis
Now much reduced with improved JES
C.Clement
Top Physics: from the Tevatron to LHC 11

12. Top Physics: from the Tevatron to LHC
Results (0.9 fb-1)
l + 3 jets
l + ≥4 jets
≥4 jets, 0 tag
C.Clement
Top Physics: from the Tevatron to LHC 12

13. Top Physics: from the Tevatron to LHC
Source
Uncerntainty on B(t→Wb)
Statistical
–0.064
b-tagging
–0.049
Multijet background
–0.017
Others
–0.021
Total error
–0.084
B(t→Wb)
σtt
systematic migration b/w sigma and Br
B(t→Wb) = (stat+syst)
σtt = (stat+syst)0.49(lumi) pb
230 pb-1 Phys. Lett. B 639 (2006)
B(t→Wb) =
C.Clement
Top Physics: from the Tevatron to LHC 13

14. Top Physics: from the Tevatron to LHC
Lower limit on B(t→Wb)
Implicit assumption of this analysis: B(t→Wq) =1
Feldman-Cousins
Limits on |Vtb| can be derived
- using |Vtb|=√B(t→Wb)
(w. unitary 3x3 CKM matrix)
|Vtb| > at 95% C.L.
- no assumption, using |Vts| and |Vtd| experimental constraints:
|Vtb| > at 95% C.L.
- so for precise Vtb look into single top ...
68% CL : B(t→Wb)>0.904
95% CL : B(t→Wb)>0.812
C.Clement
Top Physics: from the Tevatron to LHC 14

15. Top Quark Charge Lift ambiguity present in all top analyses!OR ?
Lift ambiguity present in all top analyses!
t→W+b or ”t”→W-b
Beautiul mirror... t b Q1 Q4
+2/3
-1/3
-4/3
mixing
M(Q4)~175GeV
Mtop~270GeV
Test exotic models...
Phys.Rev. D65 (2002)
053002
C.Clement
Top Physics: from the Tevatron to LHC 15

16. Top Physics: from the Tevatron to LHC
Ingredients OR ?
kinematic fit + =
Qtop
What is the expected shape of Qtop for
SM top
”top” with 4e/3 charge?
C.Clement
Top Physics: from the Tevatron to LHC 16

17. Top Physics: from the Tevatron to LHC
Analysis strategy
Double tagged events
Discriminate between
|Qtop| = 2e/3 and |Q”top”|=4e/3
Two |Qtop| per event
Use the pure sample
-- lepton+4≥jets events with 2 SVT
Compute the jet charge of
the 2 b-tagged jets
Associate the b-jets to correct
W boson (charged lepton)
Combine the 2 jet charges and the
lepton charge to derive the 2 |Qtop|
Compare the observed |Qtop|
with expected SM and exotic distributions
S/B~10
C.Clement
Top Physics: from the Tevatron to LHC 17

18. Top Physics: from the Tevatron to LHC
Jet Charge Algorithm
pTi,qi
Compute jet charge only for b-tagged jets
(2 per events)
Jet charge =
Optimizaton on MC gives a=0.6
Sum over tracks with
pT>0.5GeV,
ΔR(track, jet) <0.5 of the jet axis
Algorithm:
Derive expected shape of Qjet from data
with minimal input from simulation
C.Clement
Top Physics: from the Tevatron to LHC 18

19. Top Physics: from the Tevatron to LHC
Jet Charge Performance in Data
Tag and probe method in ”pure” events
In reality:
Is it pure ? ? flavor excitation? g→ ?
B→
B →D → 
→ 
B→ light hadrons →
Charge misidentification _ bb
Tight di-jet sample
>3.0
bbar Discriminant Power
MC truth on tag side
Tag & probe: Z→bb
Tag and probe: data
Ideal case: sign of q = sign of qb _ bb _ cc _ bb
´ _
Bo→ Bo
Charge flipping processes
C.Clement
Top Physics: from the Tevatron to LHC 19

20. Top Physics: from the Tevatron to LHC-
Is the triple tag sample pure ”bb”?
The fraction of c-jets in the triple tag sample is determined by pTrel fit of the order of a few percents,
Flavor excitation/ splitting?
>3.0
2 b-jets back to back dominate
C.Clement
Phys. Rev. D 65, (2002)
Top Physics: from the Tevatron to LHC 20

21. Top Physics: from the Tevatron to LHC-
p.d.f.’s Qb, Qb, Qc, Qc from data... - - -
P+ (Qjet) = (1-xc) (1-xflip)Pb (Qjet)+ (1-xc)xflip Pb + xc Pc _ cc
Fraction of charge
flipping processes
30±1% from MC,
Cross checked on data
Fraction of derived
from pTrel spectrum
of  (1+2-1%)
p.d.f of Qjet
in probe jet
Tight di-jet sample +
Similar equation for P- (Qjet)
4 Unknown p.d.f’s
Pb, Pb, Pc, Pc - -
C.Clement
Top Physics: from the Tevatron to LHC 21

22. Top Physics: from the Tevatron to LHC-
p.d.f.’s Qb, Qb, Qc, Qc from data... -
Tight di-jet sample - -
P+ (Qjet) = Pb (Qjet) Pb Pc
P- (Qjet) = Pb (Qjet) Pb Pc
P´+(Qjet) = Pb (Qjet) Pb Pc
P´- (Qjet) = Pb (Qjet) Pb Pc - - -
loose di-jet sample -
Correct for difference in
t→Wb and bb kinematics
C.Clement
Top Physics: from the Tevatron to LHC 22

23. Top Physics: from the Tevatron to LHC
SM Top Charge Observables
We need an observable and an expectation for the ”2e/3” and ”4e/3” scenarios
Consider only lepton+jets channel (e/µ + 4 jets) double-tagged events
Two top quarks in the event  measure the charge ”twice”
Use kinematic fit to assign b-jets to correct W-bosons in MC
qb and qB are taken from the data derived jet charge templates
qb = b lept. side
qB = b hadr. side qB qB qb qb
C.Clement
Top Physics: from the Tevatron to LHC 23

24. Top Physics: from the Tevatron to LHC
Result on ~0.4 fb-1 of D data
16 l + jets double tags
D0 0.4fb-1
Likelihood ratio test b/w 4e/3 and 2e/3 scenarios
Bayes factor =Prob(data|SM) / Prob(data|EX) = 4.3
agrees much better with 2e/3 than 4e/3
Probability of 4e/3 to fluctuate to observation 7.8% (p-value)
Sources of Uncertainties
strongly statistics limited
Data calibration method
cc fraction
Charge flipping processes
pT, eta spectra in triple tag sample
Flavor creation in triple tag sample
Statistics in triple tag sample
Kinematic fit
Top quark mass
Jet energy scale, resolutions
fQ4 <0.52 at 68% C.L.
σtt
PRL 98, (2007)
C.Clement
Top Physics: from the Tevatron to LHC 24

25. Top Physics: from the Tevatron to LHC
Conclusion
Check that the object at GeV is a fully SM top quark
Start to get handle on detailed properties of the top quark are being measured by the Tevatron experiments,
More to come with increased luminosities and ATLAS and more to achieve before full picture is clear
C.Clement
Top Physics: from the Tevatron to LHC 25