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A measurement of σ (ttbar) & a search for V+A structure in the tWb vertex in CDF

A measurement of σ (ttbar) & a search for V+A 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. Top pair production at the Tevatron.

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A measurement of σ (ttbar) & a search for V+A structure in the tWb vertex in CDF

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  1. A measurement of σ(ttbar) & a search for V+A 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 0404:068 (2004) Kidonakis & Vogt PRD 68 114014 (2003) Very rare process One top pair each 1010 inelastic collisions at s = 1.96 TeV At √s=1.96 TeV: 85% qq 15% gg σ = 6.7 pb (MTOP=175GeV) At √s=14 TeV: 10% qq 90% gg σ = 833 ± 100 pb High Pt lepton triggers are very important

  3. q’, n q, l+ W+ t b p p t b q, l- W- q’, n 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 lepton+jets 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 V+A structure.

  4. The Top dilepton channel event selection b t e,µ W   W e,µ t b q q • Two High Pt leptons: • e(Et>20GeV) or µ (Pt>20GeV) • 3 dilepton channels: ee,eµ,µµ • Reject cosmics, conversions,trileptons • Veto Z´s: • ee & µµ 76< Mee,µµ< 106 GeV • MET>25 GeV: • “L-cut” • NJETS>=2 • (ET>15 GeV & |η|<2.5) • HT>200 GeV • Opposite sign leptons. Data used here Central electron and muon triggers and plug electron plus MET

  5. b t e,µ W   W e,µ t b q q ttbar Acceptance • 1M ttbar PYTHIA 6.1 MC • MTOP=175GeV • |zvtx|<60cm (95.5% CDF luminous region) • Araw=0.873 +- 0.012% (ee : µµ: eµ) (22%:25%:53%) • Acorr=0.732 +- 0.012 % • (ee : µµ: eµ) • (↓90.1%:↓78.1%:↓83.7%)

  6. e,µ  q  W q   Z/*  q e,µ  W q  e,µ l Z q l e,µ q,l W q(') q('),ν The backgrounds: WW,WZ,Z→ττ qq´→γ*/Z→ττ +(≥2 p) σZττ=333 +- 33 pb qq´→WW→lνlν+(≥2p) σWW=12.4 +- 0.8 pb qq´→WZ→(qq´)(ll´) qq´→WZ→(lν)(l´l´´) σwz=3.65 +- 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

  7. e,µ  e,μ q e,μ q q q W  Instrumental backgrounds: “Fakes” and DY • Origin: manly W(lv)+>=3 jets, others Wbb,Wcc,Wc, QCD • Jets faking high Pt electrons: η, π0, π+, π- • 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/Eem<0.125 • High Pt isolated track with E/P<1 • Applied to “fakeable” events l1+d2+MET+>=2 jetsin W+jets data. • Drell-Yan qq´→γ*/Z→ee,µµ +(≥2 p) Methodology: • Use DATA in the high MET region inside the Z peak (76 <Mll<106) • 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,>=2

  8. CONTROL REGIONS SIGNAL REGION: NJETS>=2 HT>200GeV OS leptons NJETS=0,1 CONTROL REGIONS 2 high Pt leptons, Z veto, high Met

  9. SUMMARY 750 pb-1

  10. σtt in 750 pb-1 M.Cacciari,et al. JHEP 404,68 (2004)

  11. KINEMATICS (I)

  12. KINEMATICS (II)

  13. Top dilepton candidate with one b-tag • Nrun=193051, Nevt=1108405 • 1st e: Pt=114.1 GeV Eta=-0.4 • 2nd e: Pt=60.3 GeV Eta=0.4 • 1st jet: Et=40.3 GeV Eta=0.0 • 2nd jet: Et=40.0 GeV Eta=1.1 • MET Et=55.0 GeV Eta=1.1

  14. SIGNATURE • 1 Isolated lepton • PT>20GeV/c • Met>20GeV • >=3 jets with Et>15GeV/c • BACKGROUNDS • W+jets with HF (gbb, cc) • Mistags • Non W background From Lepton+Jets WG: 695pb-1 >=1 b-tag HT >200 GeV >=2 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

  15. CDF Summary XS (750 pb-1)

  16. Is it really SM Top ? SM f V+A=0 f-=30% f0=70% f+=0% non SMf V+A = 1 f-=0 f0=70% f+=30%

  17. Mlb SAMPLES: L+jets single-btagged: 1D template, one pairing, one Mlb value L+jets double-btagged: 2D template: 2 lepton-bjet pairing 2 entries per event: Mlb(1) vs Mlb(2) Dileptons Idem L+jets Hipothesis: leading jets are b-jets

  18. Binned Log likelihood method SM: f Free parameters Dilepton Templates: ttbar V+A,V-A (MC, Alpgen+Pythia) DY/WW/WZ MC: (Alpgen+2p) FAKES fakeable events in W+jets data X FR(PT)

  19. Pseudo-experiments: test robustness • Hypothesis: f V+A= f TRUE[0,1] • Fluctuate N expected with gaussians: • N PE,EXP BKGR = σEXP BKGR L • N PE,EXP V+A= εV+AσTTBAR f TRUE • N PE,EXP V+A= εV+AσTTBAR f TRUE • Compute expected fractions of BKGR, and signal V+A,V-A • Fill ramdomly BKGR,V+A,V-A pseudo-templates with NPE,BKGR, N PE,V+A, NPE,V-APE events from BKGR,V+A,V-A templates. • Perform fit: input f TRUEfree parameters f V+A σttbar σBKGR, output f V+A FITTED

  20. 1000 PE´s with a fixed true value of fV+A For each pseudo-experiment: Get 95% CL by ‘scanning’ the likelihood function along the fV+A axis. After all 1000 PE’s at different f V+A true: a distribution of 95% CL’s. 95% CL contours: 1K PE scanning f TRUE in [0,1] Confidence Level SYSTEMATICS NOT YET INCLUDED

  21. 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 l+jets 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 V+A 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 fV+A with CDF data.

  22. BACKUP SLIDES

  23. From Run I: • Solenoid • Central muon system • Central calorimeter ||= 1. CDF Run II Detector • New For Run II: • Front-end DAQ • Trigger:Track (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.

  24. 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 ? 5 orders of magnitude 11 years after the top quark discovery

  25. Where do I get this? Data used here • 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

  26. Acceptance versus Top Mass Raw acceptance changes by +0.055% per Δ(MTOP) = 1 GeV or Δ(Acc) = -0.016%

  27. 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

  28. Lepton+Jets Channel: b Tagging 2 b tags HT>200GeV

  29. Top dilepton candidate Nrun=193031 Nevt=7271850

  30. From Tevatron to the LHC

  31. e & μ in • Central e: ||<1.2 • Et>20-25 GeV • EM cluster + Drift chamber track,Pt>10 GeV • Plug e: 1.2<||<2.0-2.8 • EM cluster (+ Silicon track) • measured with Zee Trigger : 100%, Et>30 GeV ID  : >[80-94]% • Loose : • High Pt isolated track pointing to a gap in the - coverage ||<1.2 • Tight  : • pointing to a  -stub ||<1. •  measured with Z  • Trigger : 88%-95% • ID  : 85%-90% e &  at CDF Run II Drift chamber Track quality |d0|<0.2,0.02 cm MIP: Eeom<2 GeV Ehad<6 GeV E Ehad/Eem<0.055,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.

  32. 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 V+A in the tWb vertex. • Mlb observable. • Likelyhood technique. • Pseudoexperiments and expected limit. • Conclusions & Prospects.

  33. e & μ in • Central e: ||<1.2 • Et>20 GeV • EM cluster + Drift chamber track,Pt>10 GeV • Plug e: 1.2<||<2.5 • EM cluster (+ Silicon track) • Loose : • High Pt isolated track • (drift chamber) • pointing to a gap in the - coverage • Tight  : • pointing to a  -stub e &  at CDF Run II Drift chamber ID: Track quality |d0|<0.2,0.02 cm MIP: Eeom<2 GeV Ehad<6 GeV ID: Ehad/Eem<0.055, Shower profiles.. E • Veto cosmics using timing and track information. • Veto  from jets (mostly b) using calorimeter isolation.

  34. Cosq* in Lepton+Jets: (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) W Helicity Combined result: f+ = 0.04 ± 0.11 (stat) ± 0.06 (syst) 0.0<f+<0.25 at 95%CL CDF combined (162pb-1): 0.0<f+<0.27 at 95%CL

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