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Physics with Top Quarks

Physics with Top Quarks

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Physics with Top Quarks

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  1. t 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

  3. Top Rediscovered in Run 2 Top Rediscovered in Run 2!

  4. Periodic Table of the Particles 5 orders of magnitude!

  5. Top Event Decays • 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

  6. Events Characterized by W Decays tWb ~ 100%

  7. Dilepton Decay Mode

  8. Lepton+Jets Decays

  9. All-Hadronic Decays

  10. - Jet 2 MIP signal In calorimeter secondary vertex interaction point Jet 1 interaction point secondary vertex Muon + jets event with 2 tagged b-quark jets

  11. 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

  12. Electroweak Single Top Production s-channel ~1 pb t-channel ~2 pb New Resonance Production?

  13. Chicago WrigleyField Fermilab, Chicago, IL U.S.A. Booster CDF DØ Tevatron p source Main Injector Fermilab Tevatron

  14. Top Quark Production • Production mechanism • Top pair cross section • EWK production (single top) • Forward-backward charge asymmetry • Resonances decaying to top

  15. Does t-tbar production match NLO prediction? (ggtt)/(pptt) = 0.07 ± 0.16 (NLO: gluon~15%, quark~85%) (neural net analysis: fg < 0.33 @ 68% CL)

  16. Nevents - Nbackground (tt) = Luminosity *  t-tbar! • Top Pair Production • Cross Section: • As QCD predicts? • Only SM top? • By heavy particles?

  17. Event topology Discriminant: No b-jet tagging Top pair Requiring two identified b-jets: Ultra pure top pair sample Top pair

  18. Many new dilepton measurements! Tau Lepton channels difficult! *BR(ttl++2+2b) = 0.19±0.08(stat) ± 0.07(syst) !

  19. Z/Dib tt Wbb non-W Mistags Wcc Wc • Single Top Production: • Rate  |Vtb|2 in SM • Sensitive to H+, 4th gen, • W’, FCNC, … • Signature ~ SM Higgs • SM cross section ~3 pb • Backgrounds! • Best channels S/B~1/20 • Signal smaller than • background uncertainty!

  20. 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

  21. D0 Single top results DØ Combination: 3.6 Expected significance: 2.3 3.4! D0 Results: Search for Single Top Boosted decision trees Expected sensitivity: 2.1 First direct limit on Vtb: 0.68 <|Vtb|< 1 @ 95%CL s+t= 4.9 ±1.4 pb

  22. Results for Single Top from CDF 3.1 Evidence New CDF Results: Search for Single Top 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

  23. CDF Run II Preliminary L=1.5 fb-1 s-channel t-channel Using the Matrix Element cross section measurement, CDF determines |Vtb| assuming |Vtb| >> |Vts|, |Vtd| |Vtb|= 1.02 ± 0.18 (expt) ± 0.07 (theory) Z. Sullivan, Phys.Rev. D70 (2004) 114012 D0 |Vtb|>0.68

  24. Forward-Backward Production Asymmetry Forward-Backward Production Asymmetry Afb No asymmetry expected at LO 4-6% expected at NLO in parton frame J. Kuhn, et al. Diagram interferences for qq Smaller asymmetry in lab frame Reduced Asymmetry in tt+jet -- Uwer, et al.

  25. Afb > 0 < 0 First Afb Result from D0 How would new physics look? F: fraction of top pair events produced via Z' resonance For MZ' = 750 GeV: F < 0.44 (expected) F < 0.81 (observed) Afb= 12± 8(stat) ± 1(syst) % (Uncorrected for reconstruction)

  26. Afb CDF Compare with D0 result: Afb(bkg sub)=(14.4± 6.7(stat) ) % First Afb Results from CDF NLO: (4-7%) in y*Ql Afb=(28± 13(stat) ± 5(syst) ) % (Fully corrected)

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

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

  29. Top Properties • Top Mass • Top Quark Width • Charge of Top Quark

  30. Top Quark Mass: Important EWK Parameter • 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… What an experimentalist sees

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

  32. 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

  33. New Ideas DILEPTON LEPTON+JETS New Ideas! Top mass with cross section constraint: trades stat uncertainty for theory dilepton Top mass extracted from cross sections: Compare to theory and across channels! Consistent with kinematic measurement? Cacciari, Mangano, et al hep-ph/0303085

  34. Top mass Best per channel Mtop=171.6 ± 2.0 GeV/c2 Snapshot: most precise 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

  35. Top mass summary and combination World Average March 2007: Mtop=170.9 ± 1.9 GeV/c2 See P. Petroff’s Talk (next) for electroweak implications D0-CDF Joint Systematics Effort Underway! New combinations will follow…

  36. Top quark width Top Quark Width t < 12.7 @ 95% CL Mt = 175 GeV

  37. Top Quark Charge: -2/3? Top Quark Charge: -2/3? f+ = 0.87 P-value = 0.31 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

  38. Top Event Decays • W helicity (V-A) • Toplight charged higgs • Branching Ratios • Top sample (W+c) • FCNC

  39. t-W-b Coupling V-A? t-W-b Coupling The V-A character of the decay makes the helicity of the W only F0 = 0.70, F- = 0.30, F+ = 0 (left-handed, longitudinal, right-handed) cos* = angle between lepton and top in W rest frame

  40. W helicity 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 f+<0.14 @ 95%CL CDF1(1.7 fb-1) : f+=0.01 ± 0.05 ± 0.03 f+<0.12 @ 95%CL CDF2(1.7 fb-1) : f+=-0.04 ± 0.04 ± 0.03 f+<0.07 @ 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

  41. Simultaneous measurement of  and Branching Ratio +0.094 Simultaneous measurement of  and Branching Ratio New measurement by D0! See Talk by K. Tollefson Today: Tevatron Striking Results +0.87 tt = 8.10-0.82 (stat+syst) ± 0.49 (lumi) pb R= 0.991-0.085 (stat+syst)

  42. Limits on charged higgs Ratio of Cross Sections: Limit 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): B(tH+b)<0.35 @95% CL Expected: B(tH+b)<0.35 @95% CL Previous CDF result with 200 pb-1 explores other parameter spaces.

  43. 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

  44. Summary

  45. Backups

  46. D0 single top expected and observed

  47. How to extract top width

  48. Afb and higher orders

  49. 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% CDF Single Top: What Changed ? • 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