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Top physics at CDF
Koji Nakamura on behalf of CDF collaboration
"New Developments of Flavor Physics"
March 9th, 2009
Top Quark at Tevatron What is top quark?
Evidenced in 1994 by CDF, discovered in 1995 by Tevatron
The heaviest quark so far. The Mass is about 172 GeV. Now We have much more data to analyze top quark
properties.
24 Aug, 2008
Record : 3.8 fb-1
Good Data: 3.2 fb-1
Top Quark at Tevatron What is top quark?
Evidenced in 1994 by CDF, discovered in 1995 by Tevatron
The heaviest quark so far. The Mass is about 172 GeV. Now We have much more data to analyze top quark
properties.MassCharge
Production Cross SectionFwd-Bwd AsymmetryProduction Mechanism
W helicity
New Physics FCNC ttbar resonance charged Higgs ……
Top Quark properties in pair production
30% : 70%
Top Quark at Tevatron
~ 6.7 pb
~ 2.9 pb
What is top quark? Evidenced in 1994 by CDF, discovered in 1995 by
Tevatron The heaviest quark so far. The Mass is about 172 GeV.
Now We have much more data to analyze top quark properties.Single top production is allowed in SM
Both CDF and D0 Submitted to PRL CDF
DØarXiv.org:0903.0885
arXiv.org:0903.0880
Lumi : 3.2 fb-1Expected : 5.9 σObserved : 5.0 σ
Lumi : 2.3 fb-1Expected : 4.5 σObserved : 5.0 σ
Observation
Observation
Why Single Top Quark?
Production rate is proportional to |Vtb|2
t = (1.98 ± 0.25) |Vtb|2 pb
s = (0.88 ± 0.11) |Vtb|2 pb
Top Polarization study
Probe Non Standard Model phenomena
Single top quarks are 100% polarized in SM Can test this with angular distribution of top decay
Can search for heavy W’ boson or H±
Technical MotivationTest of the methodology for Higgs search (the same final state as the WHlνbb signal)
2 or 3 high Pt jets (Pt>20 GeV)
One high Pt lepton (Pt>20 GeV) Large
Missing Energy (Et>25 GeV)
Event topology
difficulty
Singletop production with decay into lepton + 2 jets final state
Singletop
Top pair
Signal is hidden under the huge bkg
Multivariate analyses are needed
Dominant process of 4 jets bincounting method is possible
Background (at least 1 b-tag)
Analysis strategy CDF Data Set Signal Model Background Model
Event Selection
Likelihood Function
Multivariate Analysis
Blind analysis
Split in sub setof different purity
Cross section measurementD
iscrimin
an
t
|Vtb| measurement
Significance and xsec limit
Lepton Trigger Event Met + Jets Trigger Event
Neural Network
Matrix Element
Boosted Decision Tree
Non triggered lepton No lepton
Neural Network
Multivariate Analysis
Lep+jets
Likelihood AnalysisUsed projective likelihood function to combine the separation power of several variables.
t-channel optimized analysis s-channel optimized analysisExample of input variables
2 b-tag events OnlyExample of input variables
HTQ*η pTMlνb
Result of Likelihood Analyses t-channel optimized analysis s-channel optimized analysis
pb 1.6σ 0.80.7ts
pb 1.5σ 0.9
0.8s
Expected significance: 4.1 σObserved significance: 2.4 σ
Expected significance: 1.1 σObserved significance: 2.0 σ
s- and t-channel are the signal s-channel is the signal
2 b-tag events Only
Combination of Likelihood Analyses
To obtain s- and t-channel cross section in s-t plane,We perform s- and t-channel cross section fit simultaneously.
Combine following 2 analyses: 1-b-tag events -- optimized to t-channel 2-b-tag events -- optimized to s-channel
pb 1.0σ
pb 1.4σ
t
s
Matrix Element Analysis
Using Matrix Element information to calculate probabilities for seven different underlying processes: s-channel, t-channel, Wbb, tt, Wcc, Wc+jet and Wgg.
The other MV TechniquesNeural Network analysis Boosted Decision Tree analysis
Sequence of binary splits using the discriminating variable which gives best sig-bkg separation.
An orthodox NN analysis using Neuro Bayes Program 18-25 variables are used
pb 0.61.8σ ts
Expected significance: 5.2 σObserved significance: 3.5 σ pb 2.1σ 0.7
0.6-ts
Expected significance: 5.2 σObserved significance: 3.5 σ
Result of NN and BDT analyses Neural Network analysis Boosted Decision Tree analysis
Combination : 5 lep+jets analysis
Discriminant outputs from analyses (LFT, LFS, ME, NN, BDT ) are combined into a single, more powerful super discriminant (SD) using neural networks(NEAT).
pb 2.1σ 0.60.5-ts
Expected significance:
> 5.9 σObserved significance:
4.8 σ
MET+jets without lepton channel
Using no Lepton events by MET+jets Trigger.Independent sample from lepton+jets analysis.Using NN based event selection and NN based discriminant. Challenging!! Huge QCD background…
pb 4.9σ 2.52.2-ts
Expected significance: 1.4 σObserved significance: 2.1 σ
CDF Combination and Singletop Conclusion
Finally, we combined Super Discrimant analysis and no Lepton analysis.
Expected significance: > 5.9 σObserved significance: 5.0 σ
|Vtb|=0.91± 0.11 (exp.) ± 0.07 (theory)
Assuming no anomalous coupling 2SM
tbSM
measured2measuredtb |V|
σσ
|V|
|Vtb|>0.71(95% CL)
pb 2.3σ 0.60.5-ts
Cross section:
|Vtb| calculation:
ttbar propertiesL>=2.7 fb-1 result only(second half of 2008 and 2009)
Top Quark Mass Measurement Top Quark production cross section W helicity Forward Backward asymmetry ttbar production mechanism Search for the FCNC top decay Search for the stop Mimicking Top Event Signatures Search for charged higgs in top decay Search for the t’ quark ……
backup
Most of analysis fit the top quark mass with in-situ JES systematic.
The uncertainty of the top mass result is already systematic dominant.
0.85% precision 10% improved We need reconsidering systematics.
e.g. New Systematic Uncertainty Color Reconnection: A Variation of the Phenomenological description of color reconnection between final state particles.
M top = (172.6 ± 0.9stat ± 1.2syst) GeV/c 2
Added here for the First Time !!
Top Mass measurement Combination
Top Mass measurement New ResultTemplate Method 3.0fb-1 : l+jets
Mtop = 171.8 ± 1.5 (stat.+JES) ± 1.1 (syst.) GeV/c2
M top = (172.1 ± 7.9stat ± 3.0syst) GeV/c
2
Lepton Pt 2.7 fb-1
Mtop = 171.8 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2
Δ JES =
0.4
0 ±
0.26
σ
Matrix Element 3.2fb-1
Mtop = 174.8 ± 1.7(stat.) ± 1.9(syst.) GeV/c2
All Had. 2.9fb-1 : template with NN selection
Top Cross section Combination @Mtop=175 GeV
σpre = 6.7 ± 0.8stat ± 0.4syst ± 0.4lumi pb.
Di-lepton : 2.8 fb-1
σtag = 7.8 ± 0.9stat ± 0.7syst ± 0.4lumi pb.
σttbar = 7.08 ± 0.38 (stat) ± 0.36 (syst) ± 0.41 (lumi) pb
Lepton+jets with NN : 2.8 fb-1
Uncertainty is dominated by Luminosity Using ratio of σttbar/σZ 6%(lumi)->2%(theory)
http://www-d0.fnal.gov/Run2Physics/top/http://www-cdf.fnal.gov/physics/new/top/top.html
Following pages describe more detail
Jet Clustering and energy correction
Clustering
Summing tower energies in ΔR( ) =0.422 φη
Correction
Relative correctionMinimum bias correctionAbsolute value correctionUnderling event correctionOut of cone correction
S-channel optimization search
t-channel s-channel top pair
Tevatron 1.98 pb 0.88 pb 6.7 pb
LHC 250 pb 11 pb 870 pb
It is possible to search s-channel using 2-b-tag information
Sensitive to the new physics mainly theory with extra boson(W’,H±)
Exactly the same final state as: WH->lνbb (Golden channel at Tevatron)
It is difficult to search s-channel at LHC because…
Background Estimation
(non W)
MC basedQCD(nonW) Modeled by - failed electron - non isolated muon - jet trigger event
W+jetsPre-b-tag events
fixed
Missing Et
data
2b-tagged events
b-taggingW+jets : mistag weightW+bb, W+cc : HF fraction
QCD(nonW) x mistag weight
Acceptance Gain for Muon
Non-triggerd muon in Met+2Jets Trigger
Muon Trigger event
Lepton trigger requires CMU&CMP (CMUP) or CMX
-> add CMU only, CMP only and so on…
Single top @ CDF Acceptance +30% Significance +15%
Top Mass measurement with in-situ W->jj JES calibration
1 tag
2 tag
Mtop MjjTemplate Method
Mtop = 171.8 ± 1.5 (stat.+JES) ± 1.1 (syst.) GeV/c2
Mtop = 171.8 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2
ΔJES = 0.40 ± 0.26 σ
Matrix element (Multi-variate) Method
σZtheory = 251.3 ± 5.0 (sys) pb
σz measured= 253.27 ± 1.01(stat) +4.4-4.6 (sys) +16.63
-13.71 (lumi) pb
1/R = σZ /σttbar = 36.47 +2.06-2.29 (stat) +1.88-
1.96(sys)
ttbar cross section using Ratio σttbar/σZ
σ ttbarmeasured =6.89 ± 0.41(stat) +0.41
-0.37(sys) ± 0.14 (theory) pb
σ ttbarmeasured =1/R x σZ
theory
σttbarmeasured = 7.08 ± 0.38 (stat) ± 0.36 (syst) ± 0.41
(lumi) pb
W helicity 1.9 fb-1
the angle between the lepton as measured in the W rest frame and the W boson as measured in the top rest frame
F+ = -0.04 ± 0.04(stat) ± 0.03(syst)
F0= 0.59 ± 0.11(stat) ± 0.04 (syst)F+ < 0.07 @ 95%
C.L. Matrix Element method
cos θ* template fit method
f0 = 0.637 ± 0.084 (stat) ± 0.069 (syst)
Assuming f+=0
ttbar production mechanism 2.0 fb-1
Fgg=0.53+0.35-0.37(stat.)+0.07
-0.08(syst.)
q qSpin gg
anti-parallel spin state
Spin
parallel spin state
J = 1 Jz = 1
qq annihilation gg fusion
J = 0 Jz = 0
P P
ll
Fgg = 0.07+0.15-0.07(stat+sys)
1.0 fb-1 Combination
Search For Pair Production of Stop Quarks Mimicking Top Event Signatures
Similar decay product as ttbar