Diapositiva 1

1
A measurement of s(ttbar) a search for VA
structure in the tWb vertex in CDF
Susana Cabrera IFIC(CSIC-UV)
XXXIV International Meeting on Fundamental
Physics FROM HERA AND THE TEVATRON TO THE
LHC April 2-7 El Escorial, Madrid,SPAIN
2
Top pair production at the Tevatron
Cacciari et al. JHEP 0404068 (2004) Kidonakis
Vogt PRD 68 114014 (2003)
Very rare process One top pair each 1010
inelastic collisions at ?s 1.96 TeV
At vs1.96 TeV 85 qq 15 gg
s 6.7 pb (MTOP175GeV)
At vs14 TeV 10 qq 90 gg s 833 100 pb
High Pt lepton triggers are very important
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Top pair decay signatures at CDF.

• t ?Wb 100 (Standard Model)
• Main usable event topologies
• tt ? l?l?bb di-lepton 5 e?
• tt ? l?qqbb leptonjets 30 e?
• tt ? qqqqbb all hadronic 45

1st) Test the QCD calculations of top pair
production By measuring top pair rate.
2nd) Test top decay Measuring W helicity look
for VA structure.
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The Top dilepton channel event
selection

Two High Pt leptons e(Etgt20GeV) or µ
(Ptgt20GeV) 3 dilepton channels ee,eµ,µµ Reject
cosmics, conversions,trileptons Veto Zs ee
µµ 76lt Mee,µµlt 106 GeV METgt25 GeV L-cut
NJETSgt2 (ETgt15 GeV ?lt2.5) HTgt200
GeV Opposite sign leptons.
Data used here
Central electron and muon triggers and plug
electron plus MET
5
ttbar Acceptance

• 1M ttbar PYTHIA 6.1 MC
• MTOP175GeV
• zvtxlt60cm (95.5 CDF luminous region)

• Araw0.873 - 0.012 (ee µµ eµ)
  (222553)

• Acorr0.732 - 0.012
• (ee µµ eµ)
• (?90.1?78.1?83.7)

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The backgrounds WW,WZ,Z?tt

qq??/Z?tt (2 p) sZtt333 - 33
pb qq?WW?l?l?(2p) sWW12.4 - 0.8
pb qq?WZ?(qq)(ll) qq?WZ?(l?)(ll)
swz3.65 - 0.26 pb

• Almost 100 MC driven
• Pythia (LO) for raw acceptances
• Latest NLO predictions
• MC shortcomings jet multiplicity from extra QCD
  radiation
• NJET scale factors measured from Z boson data

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Instrumental backgrounds Fakes and DY

• Origin manly W(lv)gt3 jets, others Wbb,Wcc,Wc,
  QCD
• Jets faking high Pt electrons ?, p0, p, p-
• Tracks faking high Pt muons Semileptonic B
  decays, punch-through
• Methodology
• Fake lepton rates measured in high statistics jet
  triggered data Et (20-100) GeV
• FR(Pt) Nl/Nd l electron or muon, d fakeable
  object
• Jet with Ehad/Eemlt0.125
• High Pt isolated track with E/Plt1
• Applied to fakeable events l1d2METgt2 jets
  in Wjets data.

• Drell-Yan qq??/Z?ee,µµ (2 p) Methodology
  
• Use DATA in the high MET region inside the Z peak
  (76 ltMlllt106)
• Use DY Pythia MC
• Correct non-DY sources of dileptons
• To predict the number of events outside the Z
  mass window
• To distribute them among different jet
  multiplicity bins 0,1,gt2

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CONTROL REGIONS
SIGNAL REGION NJETSgt2 HTgt200GeV OS leptons
NJETS0,1 CONTROL REGIONS 2 high Pt leptons, Z
veto, high Met
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SUMMARY 750 pb-1
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stt in 750 pb-1
M.Cacciari,et al. JHEP 404,68 (2004)
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KINEMATICS (I)
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KINEMATICS (II)
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Top dilepton candidate with one b-tag

• Nrun193051, Nevt1108405
• 1st e Pt114.1 GeV Eta-0.4
• 2nd e Pt60.3 GeV Eta0.4
• 1st jet Et40.3 GeV Eta0.0
• 2nd jet Et40.0 GeV Eta1.1
• MET Et55.0 GeV Eta1.1

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From LeptonJets WG 695pb-1
SIGNATURE 1 Isolated lepton PTgt20GeV/c Metgt20GeV
gt3 jets with Etgt15GeV/c
BACKGROUNDS Wjets with HF (g?bb, cc) Mistags
Non W background
gt1 b-tag HT gt200 GeV
gt2 b-tags
2 b tags
33 46 7.2-1.3 1.9-0.5
156 158 53.0-6.3 17.2-1.9
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CDF Summary XS (750 pb-1)
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Is it really SM Top ?
SM f VA0 f-30
f070
f0
non SMf VA 1 f-0 f070
f30
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Mlb
SAMPLES Ljets single-btagged 1D template,
one pairing, one Mlb value Ljets double-btagged
2D template 2 lepton-bjet pairing 2
entries per event Mlb(1) vs Mlb(2) Dileptons
Idem Ljets
Hipothesis leading jets are b-jets
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Binned Log likelihood method
SM f
Free parameters Dilepton Templates ttbar
VA,V-A (MC, AlpgenPythia) DY/WW/WZ MC
(Alpgen2p) FAKES fakeable events in Wjets data
X FR(PT)
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Pseudo-experiments test robustness

1. Hypothesis f VA f TRUE 0,1
2. Fluctuate N expected with gaussians
3. N PE,EXP BKGR s EXP BKGR L
4. N PE,EXP VA e VA s TTBAR f TRUE
5. N PE,EXP VA e VA s TTBAR f TRUE
6. Compute expected fractions of BKGR, and signal
   VA,V-A
7. Fill ramdomly BKGR,VA,V-A pseudo-templates with
   NPE,BKGR, N PE,VA, NPE,V-A PE events from
   BKGR,VA,V-A templates.
8. Perform fit input f TRUE free parameters f VA
   sttbar sBKGR, output f VA FITTED

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Confidence Level

• 1000 PEs with a fixed true value of fVA
• For each pseudo-experiment
• Get 95 CL by scanning the likelihood
  function along the fVA axis.
• After all 1000 PEs at different f VA true
• a distribution of 95 CLs.
• 95 CL contours 1K PE scanning f TRUE in 0,1

SYSTEMATICS NOT YET INCLUDED
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CONCLUSIONS PROSPECTS

• 11 years after the discovery and still
  elucidating..
• We have measured the ttbar production cross
  section in the dilepton channel with 750 pb-1
• This result is combined with other results from
  ljets channel achieving a precision of 12,
  close to the theoretical error of the current QCD
  calculations of the top pair production.
• A technique to search for VA top decay vertex in
  both dilepton and lepton plus jets top samples
  has been extensively tested using
  pseudoexperiment.
• Prospects
• Including systematics in the 95 CL.
• Then we will open the box and measured fVA
  with CDF data.

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BACKUP SLIDES

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CDF Run II Detector

• From Run I
• Solenoid
• Central muon system
• Central calorimeter

? 1.

• New For Run II
• Front-end DAQ
• TriggerTrack (L1) and Displaced Track (L2)
• Silicon Tracker (8 Layers) (??? ? 2.0)
• Central Outer Tracker
• (??? ? 1.0)
• Plug Calorimeters
• (1.0 ? ??? ? 3.6)
• Extended Muon Coverage (??? ? 1.5, gaps filled in)

?2.
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11 years after the top quark discovery

• 1995 Top quark discovered by CDF and D0
• Not a surprise SM quark sector completed
• But top mass was surprisingly high.
• 2006 (still elucidating!)
• Single top remains undiscovered.
• Precision measurements
• Pair production cross-sections
• Now CDF 12
• Mtop (Moriond 2006) 172.5 2.3 GeV
• Top properties (besides the top mass) studies
  with almost 1 fb-1 .
• Is it really a Standard Model Top ?

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• Delivered 1.2fb-1
• Accelerator doing very well
• Record peak inst. luminosity
• 1.79x1032/cm2s (11/10/2005)
• If no further improvements
• 4fb-1 in 2009
• Electron cooling on track
• Could get 8fb-1 in 2009!
• Detectors doing well
• Upgrades finishing up to deal with luminosity
  increase coming in 2006
• D0 installing silicon now

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Acceptance versus Top Mass
Raw acceptance changes by 0.055 per ?(MTOP)
1 GeV or ?(Acc) -0.016
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XS versus TOP MASS
At a top quark mass of 172.0 - 2.7 GeV/c2 (CDF
750 pb-1, March 2006) The combined cross
section is 7.53-0.87 pb
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LeptonJets Channel b Tagging
2 b tags
HTgt200GeV
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Top dilepton candidate
Nrun193031 Nevt7271850

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From Tevatron to the LHC

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e ? at CDF Run II
e µ in

• Central e ?lt1.2
• Etgt20-25 GeV
• EM cluster Drift chamber track,Ptgt10 GeV
• Plug e 1.2lt?lt2.0-2.8
• EM cluster ( Silicon track)
• measured with Z?ee
• Trigger ? 100, Etgt30 GeV
• ID ? gt80-94

Loose ? High Pt isolated track pointing to a
gap in the ?- coverage ?lt1.2 Tight ? pointing
to a ? -stub ?lt1. ? measured with Z?? ? Trigger
? 88-95 ID ? 85-90
Drift chamber
Track quality d0lt0.2,0.02 cm MIP Eeomlt2
GeV Ehadlt6 GeV
E
Ehad/Eemlt0.055,Shower profiles, Track
quality,showermax matching

• Veto cosmics using timing information and track
  information.
• Veto ? from jets (mostly b) using
  calorimeter-Isolation
• Veto e coming from photon conversions using track
  information.

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THE OUTLINE

• Top pair production.
• The Dilepton channel.
• Event selection.
• Signal acceptance.
• Background estimates.
• Main Systematics XS measurement.
• The Lepton plus jets channel results
• Latest XS results from CDF.
• Top properties.
• Measurement of f VA in the tWb vertex.
• Mlb observable.
• Likelyhood technique.
• Pseudoexperiments and expected limit.
• Conclusions Prospects.

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e ? at CDF Run II
e µ in

• Central e ?lt1.2
• Etgt20 GeV
• EM cluster Drift chamber track,Ptgt10 GeV
• Plug e 1.2lt?lt2.5
• EM cluster ( Silicon track)

Loose ? High Pt isolated track (drift
chamber) pointing to a gap in the ?- coverage
Tight ? pointing to a ? -stub
Drift chamber
ID Track quality d0lt0.2,0.02 cm MIP Eeomlt2
GeV Ehadlt6 GeV
ID Ehad/Eemlt0.055, Shower profiles..
E

• Veto cosmics using timing and track information.
• Veto ? from jets (mostly b) using calorimeter
  isolation.

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W Helicity

• Cosq in LeptonJets (230pb-1)
• 2 Template analysis
• B tagging used
• Topological variables
• c2 fit is used for lepton matching (purity 60)

• Lepton PT in dilepton (370pb-1)

Combined result f 0.04 0.11 (stat) 0.06
(syst) 0.0ltflt0.25 at 95CL
CDF combined (162pb-1) 0.0ltflt0.27 at 95CL