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Top Physics at CDF

Top Physics at CDF. Gervasio Gómez Instituto de Física de Cantabria Corfu-2005. History I. 1964: CP violation in Kaon system 1973: Kobayashi & Maskawa predict 3 quark generations 1970-73: Standard Model (SM) 1975-77: discovery of t lepton (3rd generation)

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Top Physics at CDF

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  1. Top Physics at CDF Gervasio Gómez Instituto de Física de Cantabria Corfu-2005

  2. History I • 1964: CP violation in Kaon system • 1973: Kobayashi & Maskawa predict 3 quark generations • 1970-73: Standard Model (SM) • 1975-77: discovery of t lepton (3rd generation) • 1977: resonance observed in p+nucleonm+m-: (b-bbar) discovererd • Study of b quark properties • Qb=-1/3 (1978) y (1982) • I3=-1/2 (1984) • Implies existence of an additional quark (top): 3rd generation weak isospin partner of the b quark • A long search for the TOP quark begins! Corfu, 6-Sept-2005

  3. Why must top exist? Once determined Cancellation of anomalies such as: Requires existence of a t quark with: All anomalies cancel exactly if, for each family: Corfu, 6-Sept-2005

  4. History II • 1983: Discovery of W, Z with masses as predicted in SM • 1994: G(Z) in LEP & SLC exclude a 4th generation neutrino with Mn<MZ/2 • Top is almost certainly the last SM fermion • 1995: precision EW measurements • Mtop inferred from higher order EW corrections which depend on the fermion masses • Mtop  178 GeV/c2 • 1995: discovery of top in CDF and D0 • Mtop  175 GeV/c2 • By far the heaviest fundamental particle • about 200 times heavier than the proton! • Mass  EW scale • Special role in EWSB? (origin of fermionic mass) • Higgs is the only SM particle which has so far eluded detection Corfu, 6-Sept-2005

  5. Booster p source Main Injector and Recycler Tevatron • P-Pbar • Collisions every 396 ns • Beam energy 980 GeV • s = 1.96 TeV • Inst. Lum. ~2x1032 cm-2s-1 Corfu, 6-Sept-2005

  6. CDF Detector Corfu, 6-Sept-2005

  7. Tevatron: Top Production at Tevatron single top: top-antitop pairs: 85% ~2 pb 15% ~1 pb ~ one top event every 10 BILLION inelastic collisions Corfu, 6-Sept-2005

  8. Hadronization time NO top hadrons Top Decay final state given by W+ W- decays Event Classification ttlnlnbb dilepton 5% ttlnqqbb lepton+jets 30% ttqqqqbb hadronic 45% here lepton = e or m Corfu, 6-Sept-2005

  9. Top Detection • Events are energetic • Large total transverse energy: Ht • Events are central and spherical • ||< 2.0, aplanarity • High energy jets and isolated leptons • missing Et from neutrino in leptonic modes • High Et jets • Two high ET b-jets • Displaced secondary vertex • Soft lepton inside jet • Possible additional jets from gluon radiation (isr,fsr) Corfu, 6-Sept-2005

  10. B hadrons are long-lived semileptonic B hadron decay Vertex displaced tracks Soft Lepton Tagging Tagging B-jets • Top events contain B hadrons • Only 1-2% of dominant W+jets background contains heavy flavor • Great S/B improvement 55% 0.5% Top Event Tagging Efficiency False Tag Rate (QCD jets) 15% 3.6% Corfu, 6-Sept-2005

  11. Top Pair Cross Section • Measure in different samples • Understand top kinematics • Understand heavy flavor content • Cross check results • Validate top samples for other top measurements • Test of SM predictions • Sensitivity to physics beyond SM • Background to Higgs and SUSY searches Corfu, 6-Sept-2005

  12. control signal includes kinematical and geometric acceptance and branching fraction Cross Section: dileptons • Selection: 2 leptons (e, m), 2 jets, high MET • Second lepton can be “loose” -- even an isolated track • Main backgrounds: DY, dibosons, & “fakes” jlepton Corfu, 6-Sept-2005

  13. Cross Section: l+jets+B-tag • Selection: 1 lepton (e, m), >=3 jets, high MET • Btag: require at least 1, 2 tags • Main backgrounds: W+HF, QCD, W+jets (mistags) ≥ 1 tag ≥ 2 tags Corfu, 6-Sept-2005

  14. x-sec: l+jets+kinematics • Selection: 1 lepton (e, m), >=3 jets, high MET • NO Btag: higher statistics, worse S/B • Main backgrounds: W+jets, QCD, EW kinematic distributions: likelihood or NN NN: Corfu, 6-Sept-2005

  15. Cross Section Measurements Measurements consistent with each other….. … and with theory error bars: red=stat, blue=total Corfu, 6-Sept-2005

  16. Standard Model Fermions SM Fermions Fermion masses are free parameters of the SM. For quarks: ~173 GeV ~330 MeV ~1.5 GeV ~500 MeV ~330 MeV ~5 GeV Corfu, 6-Sept-2005

  17. Mass in the SM Mechanism through which fermions acquire mass not fully understood In SM, Higgs mechanism: “doublet” of scalar fields in weak isospin space With potential: with m2<0 ground state=minimum=vev: EW scale Mass term in lagrangian ground state does not have original L symmetry: spontaneous EWSB Scalar particle (spin 0): Higgs (not yet observed) Boson masses: Yukawa coupling for each fermion Fermion masses: Corfu, 6-Sept-2005

  18. Top Mass Special role in EWSB? Mt  173 GeV  Dominant parameter in radiative corrections: quadratic in mt , logarithmic in mH Mt from precision EW measurements Corfu, 6-Sept-2005

  19. Measuring Mtop Challenging: LO ME final state: • Lepton+jets • Undetected neutrino • Px and Py from Et conservation • 2 solutions for Pz from MW=Mln • Leading 4 jets combinatorics • 12 possible jet-parton assignments • 6 with 1 b-tag • 2 with 2 b-tags • ISR + FSR • Dileptons • Less statistics • 2 undetected neutrinos • Less combinatorics: 2 jets CDF sees: Largest uncertainty: Jet Energy Measurement Corfu, 6-Sept-2005

  20. Jet Energy Corrections Determine true “particle”, “parton” jet E from measured jet E • Non-linear response • Uninstrumented regions • Response to different particles • Out of cone E loss • Spectator interactions • Underlying event Corfu, 6-Sept-2005

  21. Mtop: DLM • “Dynamical Likelihood Method” (see Kuni Kondo’s talk) • Likelihood vs. mt per event from LO ME for ttl+4j and “transfer functions” for quark ET  jet ET • Minimize -ln L (combined likelihood from all events) Background mapping function: measured to true mass for a given bkg fraction (14.5% for l+4j with b-tag) Corfu, 6-Sept-2005

  22. Template Technique • Determine mass of the top quark using a quantity strongly dependent on the top quark mass Mtop (usually Reconstructed Mtop) • Determine the Reconstructed Mtop per event: Minimize a 2 expression for the resolutions and kinematic relationships in the ttbar system. Choose jet to parton assignment and Pz based on best fit quality. Build signal and background templates • Obtain the measurement from the data: Compare Reconstructed Mtop from data with same from randomly generated and simulated signal at various input top mass (Mtop) and backgrounds using an unbinned likelihood fit Signal Template Background Template Data Best signal + background templates to fit the data L = Lshape x Lbackground Corfu, 6-Sept-2005

  23. Newest Template Result Combined–Log(L) in situ JES from W->jj Corfu, 6-Sept-2005

  24. Best Mtop Measurements red=stat uncertainty blue=total uncertainty Corfu, 6-Sept-2005

  25. Single Top Search • Direct measurement of |Vtb|2 • Sensitive to new physics • W’, anomalous couplings, FCNC • Final state: lepton, MET, 2 jets & at least 1 b-jet • Challenging • Small cross section • tt now background • Large additional backgrounds Corfu, 6-Sept-2005

  26. Single top MC Templates Corfu, 6-Sept-2005

  27. Summary & Outlook • All measurements consistent with SM • Several results not shown due to lack of time • Recently published or submitted: • “Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2)=1.96 TeV Using Dilepton Events”, Phys. Rev. Lett 93, 142001 (2004) • “Search for Electroweak Single Top Quark Production in p anti-p Collisions at S**(1/2)=1.96 TeV”, Phys. Rev. D 71, 012005 (2005) • “Measurement of the W Boson Polarization in Top Decay at CDF at S**(1/2)=1.8 TeV”, Phys. Rev. D71, 031101(R) (2005) • “Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2)=1.96 TeV Using Kinematic Fitting of B-Tagged Lepton+Jet Events”, hep-ex/0409029 • “Measurement of the t anti-t Production Cross Section in p anti-p Collisions at S**(1/2)=1.96 TeV Using Lepton+Jet Events with Secondary Vertex B-Tagging”, hep-ex/0410041 • “Search for Anomalous Kinematics in t anti-t Dilepton Events at CDF II”, hep-ex/0412042 • Hope for 2 fb-1 or more by end of 2007 • ds ~ 10% (now ~30%) • dm ~2-3 GeV (now 4.3 GeV from RunI) • Single Top: possible observation Corfu, 6-Sept-2005

  28. Backup Slides Corfu, 6-Sept-2005

  29. SM quick review SM quark and lepton lagrangian Predicts all experimental observations of quark and lepton interactions Covariant derivative fixed by gauge invariance under U(1)xSU(2)xSU(3) transformations: Defining: Corfu, 6-Sept-2005

  30. Fractional Systematic Uncertainty vs PT Run I Run II 2005 Run II 2004 Central  region Jet Energy Uncertainty • 2004 uncertainty • used for most mass results shown here • Dominant systematic uncertainty • New (2005) systematic uncertainty • Significant Improvement • Redoing mass analyses • Improved results soon ~factor of 2 decrease! Corfu, 6-Sept-2005

  31. Matrix Element Technique W(y,x) is the probability that a parton level set of variables y will be measured as a set of variables x • Determine mass of the top quark evaluating a probability using all the variables in the event, integrate over all unknowns • Sum over all permutations of jets and neutrino solutions • Background process probabilities are or not be explicitly included in the likelihood • Top mass: maximize i Pi (x;Mtop) • Each event has its own probability • Correct permutation is always considered (along with the other eleven) • All features of individual events are included, thereby well measured events contribute more information than poorly measured events dnis the differential cross section: LO Matrix element f(q) is the probability distribution that a parton will have a momentum q Corfu, 6-Sept-2005

  32. Template Result from CDF Systematic uncertainties –Log Likelihood vs Mtop, JES Measurement is more precise than the current world average! JES(s) Mtop (GeV) Most of these can be reduced with more data Corfu, 6-Sept-2005

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