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Top Physics at CDF
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  1. Top Physics at CDF Gervasio Gómez Instituto de Física de Cantabria Seminari del IFIC, 3-May-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! IFIC, 3-May-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: IFIC, 3-May-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 IFIC, 3-May-2005

  5. The Standard Model (SM) SM Fermions Fermion masses are free parameters of the SM. For quarks: ~175 GeV ~330 MeV ~1.5 GeV ~500 MeV ~330 MeV ~5 GeV IFIC, 3-May-2005

  6. Mass in the SM Mechanism through which fermions acquire mass not fully understood In SM, Higgs mechanism: “doublet” of scalar fields 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: IFIC, 3-May-2005

  7. Booster p source Main Injector and Recycler Tevatron • P-Pbar • Collisions every 396 ns • Beam energy 980 GeV • s = 1.96 TeV • Inst. Lum. ~5x1032 cm-2s-1 IFIC, 3-May-2005

  8. CDF Detector IFIC, 3-May-2005

  9. Tevatron: Top Production at Tevatron single top: top-antitop pairs: 85% ~2 pb 15% ~1 pb ~ one top event every 10 BILLION inelastic collisions IFIC, 3-May-2005

  10. 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 IFIC, 3-May-2005

  11. 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) IFIC, 3-May-2005

  12. 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% IFIC, 3-May-2005

  13. 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 IFIC, 3-May-2005

  14. 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 CDF most precise: IFIC, 3-May-2005

  15. Cross Section: l+jets+B-tag • Selection: 1 lepton (e, m), >=3 jets, high MET • Btag • Main backgrounds: W+HF, QCD, W+jets (mistags) CDF most precise: IFIC, 3-May-2005

  16. 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 CDF most precise: IFIC, 3-May-2005

  17. Cross Section Measurements Measurements consistent with each other….. dilepton lepton + jets hadronic … and with theory error bars: red=stat, blue=total IFIC, 3-May-2005

  18. Top Mass Mt  175 GeV  Yukawa coupling  1 Special role in EWSB? Dominant parameter in radiative corrections: quadratic in mt , logarithmic in mH Mt from precision EW measurements IFIC, 3-May-2005

  19. Top Mass in Run-I Weight in average 6% 7% 22% 58% 7% mH (GeV) Mtop all-jets D result is not included in Tevatron average: Mtop = 178.015.7 GeV/c2 IFIC, 3-May-2005

  20. 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 IFIC, 3-May-2005

  21. 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 IFIC, 3-May-2005

  22. 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! IFIC, 3-May-2005

  23. 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 IFIC, 3-May-2005

  24. Mtop: DLM • “Dynamical Likelihood Method” : ME technique • 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 (19% for l+4j with b-tag) IFIC, 3-May-2005

  25. 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 IFIC, 3-May-2005

  26. Newest Template Result Combined–Log(L) Expected error NEW IFIC, 3-May-2005

  27. Other template measurements b-tagged l+jets: Dileptons: • b-tagged l+jets w/ multivar templates: • Probability for Mt from likelihood based on MC multidimensional templates IFIC, 3-May-2005

  28. Best Mtop Measurements error bars: red=stat blue=total IFIC, 3-May-2005

  29. 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 IFIC, 3-May-2005

  30. Single top MC Templates IFIC, 3-May-2005

  31. W+ q* n l+ t SM: 0.3+0.7+0 W Helicity SM (V-A) prediction: tWT : left handed W (30%) tW0 : longitudinal W (70%) test of V-A tWb vertex Kinematic distributions for the different helicity states are different Lepton Pt IFIC, 3-May-2005

  32. dilepton and lepton+jets lepton+jets W Helicity IFIC, 3-May-2005

  33. Search for H+ IFIC, 3-May-2005

  34. Search for 4th generation t’ • Same selection as kinematic top xs • Fit Ht to t’,t,W+jets and QCD • Likelihood for different Mt’ (one such plot for each point) IFIC, 3-May-2005

  35. Other Top Measurements IFIC, 3-May-2005

  36. Summary & Outlook • All measurements consistent with SM • 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 • Reduced Jet Energy Scale uncertainty • 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 • dF0 reduced uncertainty (now 50-100%) • Mass limit on t’ IFIC, 3-May-2005

  37. Backup Slides IFIC, 3-May-2005

  38. 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 IFIC, 3-May-2005

  39. 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: IFIC, 3-May-2005

  40. W Helicity from lepton Pt l + jets dilepton IFIC, 3-May-2005

  41. Publishing Mtop for 15 years IFIC, 3-May-2005

  42. Matrix Element at D • Last result from Run I: June, 2004 • Reduced the statistical uncertainty from 5.6 to 3.6 (expected error from 7.4 to 4.4) => 2.4 times more data • Total uncertainty from 7.3 (lepton+jets CDF) to 5.3 (D0) • Run II results from D and CDF coming soon! IFIC, 3-May-2005

  43. Phase space x LO ME for top or BG (W+4j) PDFs Probability for observable x given parton y (Ex: quark ET jet ET) Mass: D0 RunI • Statistical uncertainty reduced: 5.6 to 3.6 GeV/c2 • Equivalent to Lx2.4 ! • Likelihood vs. mt for each event: • Likelihood gives effective weigh to each event • Maximize combined likelihood to extract mt mt = 180.1  3.6(stat)  3.9(syst) GeV/c2 IFIC, 3-May-2005

  44. Template Results from D • Topological • No b-tagging requirement • Construct a discriminant using topological variables (DLB) to improve S/B • At least one b-tagged jet: • no requirement on discriminant DLB • First top mass at D top mass measurement with b-tagging ttbar candidates 69 S/B~3/1 Reconstructed Mtop (GeV) ttbar candidates 94 S/B~1/1 Reconstructed Mtop (GeV) IFIC, 3-May-2005

  45. Other Matrix Element based Mtop • DLM: only a signal probability, requires b-tagging • New results with decrease JES and more data coming soon! • Ideogram: Uses same kinematic fit as D template method, and includes DLB discriminant in likelihood fit • Uses background probability IFIC, 3-May-2005

  46. Implications for MHiggs • New combined D0 mass: • Mt = 179.0 ± 5.1 GeV/c2 • New World Average: • Mt = 178.0 ± 4.3 GeV/c2 • Global EW fit using new average • LEPEWWG method • (hep-ex 0312023) • Best-fit MH 113 GeV/c2 • Upper limit @ 95% C.L. : • 237 GeV/c2 Yellow region excluded (direct search): MH < 114.4 GeV/c2 @95% CL IFIC, 3-May-2005

  47. Futuro: LHC ¡Una verdadera fábrica de top! Tevatron: x~0.18 LHC: x~0.025 0.8 to 8 ttbar/sec 1 año a baja luminosidad: 10 fb-1: 8x106 sucesos ttbar IFIC, 3-May-2005

  48. CMS y ATLAS Detectores multi-propósito adaptados al acelerador LHC: Electrónica rápida Alta granularidad Buena resolución Buena identificación de jets, muones, missing Et, vértices desplazados, trazas IFIC, 3-May-2005

  49. j2 j1 b-jet j2 j1 b-jet t t Masa del top en el LHC • Leptón+jets: • Tag 2 b-jets • Identificar leptón y MET • Usar jets con Mjj más cercano a Mw • Reconstruir Mtop=Mjjb • Pares ttbar de alto Pt: • Back-to-back • Hemisferios opuestos • Menos fondo combinatorial • Menor JES sys (alto Pt de los jets) • Pero los jets del W se sobreponen • Sumar todos los clusters en un cono alrededor de la dirección del top • Restar Underlying Event • Dependencia en DR Combinando todos los canales: dm ~1 GeV IFIC, 3-May-2005

  50. 1.6 TeV resonance Mtt Resonancias Reconstrucción de Mtt para búsqueda de resonancias SM Higgs (BR smaller with respect to the WW and ZZ decays) MSSM Higgs (H/A, if mH,mA>2mtop, BR(H/A→tt)≈100% for tanβ≈1) Otros modelos: Technicolor, strong ElectroWeak Symmetry Breaking, Topcolor, “colorons”, … IFIC, 3-May-2005