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Recent Measurements of the Top Quark from Fermilab

Recent Measurements of the Top Quark from Fermilab. Kevin Lannon The Ohio State University For the CDF and D0 Collaborations. Note to Slide Readers.

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Recent Measurements of the Top Quark from Fermilab

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  1. Recent Measurements of the Top Quark from Fermilab Kevin Lannon The Ohio State University For the CDF and D0 Collaborations

  2. Note to Slide Readers This presentation makes heavy use of animations. Several slides to do make sense unless viewed in animated form. I recommend viewing this presentation as a slide show. K. Lannon

  3. The Top Quark and the Standard Model Top quark needed to complete the “period table” of the Standard Model • Top quark discovery • Late 1970’s: Existence suggested by discovery of b quark • 1980’s: Existence required for consistency of Standard Model • Eluded experimental observation for two decades • 1995: Observed at Tevatron • Properties of top quark that made discovery difficult also make study interesting! K. Lannon

  4. Top Quark is Special Quark Masses t b c s d u GeV/c2 • Top is really massive • Comparable to gold nucleus! • In Standard Model: Mass related to coupling to Higgs (Yukawa coupling) • Top Yukawa coupling near unity (natural value?) • Why are couplings for other quarks so small in comparison? • Special relationship between top and Higgs? • Top quark decays very quickly (10-24 seconds) • Decays before hadronization • No hadron spectroscopy • Momentum and spin transferred to decay product 5 orders of magnitude between quark masses! K. Lannon

  5. The Tevatron Accelerator Highest energy accelerator in the world (Ecm = 1.96 TeV) World record for hadron collider luminosity (Linst = 2.86E32 cm-2s-1) Only accelerator currently making top quarks Run I (1992-1995) Integrated 105  4 pb-1 luminosity Discovery of the top quark Run II (2001-present) Integrated > 2.5 fb-1 and counting! Precision study of top quarks K. Lannon

  6. Tevatron Performance • Integrated luminosity at CDF and D0 • Total delivered: ~2.7 fb-1 to each experiment • Total recorded: ~2.2 fb-1 (~ 20 Run I!) at each experiment • So far for top analyses, used up to ~1 fb-1 • More analyses with 1.2-2.0 fb-1 in progress for summer • Doubling time currently ~1 year • Future: ~4 fb-1 by end of 2007, ~8 fb-1 by 2009 Integrated Luminosity Peak Luminosity Today’s Presentation: ~1 fb-1 Analyzed by Summer K. Lannon

  7. CDF and D0 Detectors • General purpose detectors capable of many different physics measurements • Top physics uses almost all detector systems D0 CDF K. Lannon

  8. Top Quark Production at Tevatron • QCD pair production • NLO = 6.7 pb • First observed at Tevatron in 1995 ~85% ~15% s-channel t-channel • EWK single-top production • s-channel: NLO = 0.9 pb • t-channel: NLO = 2.0 pb • First evidence! ??? • Other?: K. Lannon

  9. SM Top Quark Decays • Particular analyses usually focus on one or two channels • New physics can impact different channels in different ways • Comparisons between channels important in searching for new physics BR(tWb) ~ 100% K. Lannon

  10. Top Signatures b-jet: identified with secondary vertex tag Electron or muon Jet: shower of particles Neutrino: Missing ET Dilepton Lepton + Jets All Hadronic K. Lannon

  11. Top Production Rates • Like finding a needle in a haystack . . . . Needle in haystack (approx.) • Efficient Trigger • ~90% for high pT leptons • Targeted event selection • Distinctive final state • Heavy top mass • Advanced analysis techniques • Artificial Neural Networks One top pair each 1010 inelastic collisions at s = 1.96 TeV K. Lannon

  12. Top Quark Physics is Rich Parallel Sessions • Systematically limited measurements • Cross section (~12% precision) • Mass (~1% precisions) • Statistically limited measurements • Most other measurements of top quark properties • Top quark charge • Top quark production mechanism • Searches • Single top production • Resonant production • Top to charged Higgs J14, R14 J14, R14 C14, F1, X13 F1, J14, K14, R14, T14 K13, K14, J14 K. Lannon

  13. Measuring the Top Cross Section • Agreement between theory and experimental important test of top quark properties (spin, couplings, mass) • Techniques form basis for top properties measurements • Key: separating top from backgrounds • Two main techniques: Event Kinematics: central, spherical events with large transverse energy HT scalar sum of lepton, jet, and missing ET Presence of b-jets: Detected through long life-time of the B hadrons. Decays at displaced vertex K. Lannon

  14. Recent Cross Section Results L=900pb-1 L=900pb-1 Lepton + Jets Individual Measurements approaching same precision as theoretical calculation Session R14 (Monday) Excess of events with  3 energetic jets +  1 b-tag Dilepton Channel Excess of events with  4 energetic jets and “top-like” kinematics (determined by a multivariate discriminant technique • Excess of events with • Two high pT leptons • Two energetic jets • Missing ET K. Lannon

  15. Cross Section Summary • Measurements in many different channels • Experimental precision approaching theoretical uncertainty (~12%) • Working on Tevatron combination Several cross section talks in Session R14 (Monday) CDF Run II Preliminary K. Lannon

  16. Why Measure the Top Mass? • It’s the most striking feature of the top quark! • Consistency of mass and cross section  Standard Model Top? • Related to the Higgs mass through radiative corrections to the W mass • Provides indirect constraint on Higgs mass • More precision  Tighter constraint • Tevatron Run II goal • Uncertainty < 3 GeV/c2 with 2 fb-1 data • New Goal: Uncertainty ~ 1 GeV/c2 by end of Run II MW  M2top MW  ln MHiggs Summer 2006 Updated Result in Next Talk Already exceeded! K. Lannon

  17. Measuring the Top Mass is Challenging What a theorist sees: What an experimentalist sees: • Measure jets, not partons • Account for bias and resolution  Jet Energy Scale • Determine which jet should be assigned to which parton  Combinatorics (up to 720 permutations for all hadronic decay!) • Don’t measure neutrino momentum Infer pT indirectly • Extra jets from radiation confuse things K. Lannon

  18. Jet Energy Scale • Determine parton energy from measurements in calorimeter • Correct for • Detector effects • Fragmentation/Hadronization • Underlying event • Energy scale determined from data and MC • Uncertainties in jet energy scale directly affect top mass uncertainties • Leading uncertainty without special treatment! K. Lannon

  19. In-Situ Jet Energy Scale Calibration • W mass known very precisely from other measurements • Use W mass reconstructed from jets to constrain jet energy scale • Uncertainty decreases as data increases • Key reason why we’re doing better than originally projected! K. Lannon

  20. Results: Lepton + Jets Channel World’s best • Both use • Matrix element technique • In-situ JES calibration 170.9 ± 2.2 (stat+JES) ± 1.4 (syst) GeV/c2 Session T14 (Monday) 170.5 ± 2.4 (stat+JES) ± 1.2 (syst) GeV/c2 K. Lannon

  21. Results: All-Hadronic • Combines matrix element and template techniques • First incorporation of in-situ JES calibration in all-hadronic channel • This measurement more precise than expected based on past performance! Session T14 (Monday) 171.1 ± 3.7 (stat+JES) ± 2.1 (syst) GeV/c2 K. Lannon

  22. Tevatron Combination • Many more measurements than can be discussed here • Combine for better precision • Best individual measurement: 1.5% • Combination: 1.1% uncertainty! • See next talk for impact on indirect Higgs constraints Top mass measurements in Sessions F1 (Saturday), J14, K14 (Sunday), and T14 (Monday) 170.9 ± 1.1 (stat) ± 1.5 (syst) GeV/c2 K. Lannon

  23. Top Charge • Are we observing Standard Model top? • Standard Model top has charge +2/3 • Alternative hypothesis: exotic quark with charge -4/3 • Difficult to measure (“t”W+b or W-b) • W charge measured through the lepton (straightforward) • Bottom charge inferred from jet (difficult) • Correctly pair the lepton and b jet (difficult) Exclude top charge of -4/3 with 81% C.L. Session K14 (Sunday) K. Lannon

  24. Top Production Mechanism Session J14 (Sunday) • Does ratio of qq tt and gg tt match theoretical expectation? • Depends on top mass, pdfs, etc. • Could be modified by non-standard production • Exploit correlation between low pT track multiplicity and number of gluons ~85% ~15% K. Lannon

  25. The Search for Single Top t-channel s-channel • Standard Model • Rate  |Vtb|2 • Spin polarization probes V-A structure • Background for other searches (Higgs) • Beyond the Standard Model • Sensitive to a 4th generation • Flavor changing neutral currents • Additional heavy charged bosons • W’ or H+ • New physics can affect s-channel and t-channel differently Tait, Yuan PRD63, 014018(2001) K. Lannon

  26. Signal and Backgrounds Backgrounds Other EWK Single-top Signature tt High pT e or  : MET Multi-jet QCD W + Heavy Flavor W + Light Flavor (Mistags) 2 High ETjets,  1 b-tagged Must use multivariate, kinematic techniques to separate signal from background Signal / Background ~ 1/20 Signal size ~ background uncertainty K. Lannon

  27. Multivariate Analysis Techniques Combine information from several variables into a single, more powerful discriminant • Six separate analyses • Used many different multivariate analysis techniques: Decision tree, matrix element, multivariate likelihood, neural network • Only moderate correlations among discriminants  Can combine results for greater sensitivity K. Lannon

  28. Single Top Results Normalized to fit deficit Matrix Element Neural Network Expected Signal Significance: 2.5 Expected Signal Significance: 2.6 2.3! Session X13 (Tuesday) Session F1 (Saturday) K. Lannon

  29. Single Top Results Expected Signal Significance: 2.1 Expected Signal Significance: 1.8 3.4! 2.9! Session X13 (Tuesday) Session X13 (Tuesday) K. Lannon

  30. All Single Top Results D0 Combination: 3.5 Session X13 (Tuesday) K. Lannon

  31. Limit on Vtb • (single top)  |Vtb|2 • First direct limit on Vtb • No assumption about number of quark generations • Assuming Standard Model production: • Pure V-A and CP conserving interaction • |Vtd|2 + |Vts|2 << |Vtb|2 B(t Wb) ~ 100% • Bayesian limits with flat prior between 0 and 1 Session X13 (Tuesday) 0.68 < |Vtb| < 1 at 95%CL (f1L = 1) K. Lannon

  32. Summary • Many more top physics results available than could be covered here • See public webpages for CDF and D0: • http://www-cdf.fnal.gov/physics/new/top/top.html • http://www-d0.fnal.gov/Run2Physics/WWW/results/top.htm • Very exciting times in top physics at the Tevatron • Top mass uncertainty 1.1%! • First evidence for single top production: > 3! • Cross section: Uncertainty on measurements approaching theoretical uncertainties • Just beginning to gain sensitivity to many top quark properties • Great place to search for new physics! • Stayed tuned for new results this summer K. Lannon

  33. Backup Slides K. Lannon

  34. Weights in the Combination CDF and D0 both crucial for best precision Better than expected performance from all-hadronic measurement  In-situ JES calibration K. Lannon

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