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Charles Plager UCLA

_. The Truth, The Standard Model Truth, And Nothing But The Truth? A View of the Top of CDF. Charles Plager UCLA. Outline. The Tevatron. Top Quark Physics and CDF. Top Pair Cross Section. Top Quark Mass. Single Top Cross Section. Top Quark Properties. Summary.

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Charles Plager UCLA

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  1. _ The Truth, The Standard Model Truth, And Nothing But The Truth? A View of the Top of CDF Charles Plager UCLA SLAC HEP Seminar, March 5th 2009

  2. Outline The Tevatron Top Quark Physics and CDF Top Pair Cross Section Top Quark Mass Single Top Cross Section Top Quark Properties Summary SLAC HEP Seminar, March 5th 2009

  3. 350 ¢ 1030 cm–2 s–1! Tevatron Run II: 2001–2009 (2010?) • Proton-antiproton collider: √s = 1.96 TeV. • 36×36 bunches, collisions every 396 ns. • Record instantaneous peak luminosity: • Luminosity goal: 7 – 8 fb–1 of integrated luminosity by 2009, running in 2010 currently under discussion. • Two multi-purpose detectors: CDF and DØ. Fermi National Accelerator Laboratory – Aerial View Tevatron 315 ¢ 1030 cm–2 s–1. 290 ¢ 1030 cm–2 s–1. 290 ¢ 1030 cm–2 s–1. 2 km 3 SLAC HEP Seminar, March 5th 2009

  4. Tevatron Performance • Tevatron continues to perform very well: • More than 6.1 fb–1 delivered. • More than 5.1 fb–1 recorded by CDF. • Regularly record 200 pb-1 a month. The Tevatron just delivered 73 pb-1 in single week! 6.1 fb–1 5.1 fb–1 Run I Total (~100 pb-1) Tevatron Store Number SLAC HEP Seminar, March 5th 2009

  5. Outline The Tevatron Top Quark Physics and CDF Top Pair Cross Section Top Quark Mass Single Top Cross Section Top Quark Properties Summary SLAC HEP Seminar, March 5th 2009

  6. - - Top Quark History • CDF and DØ Run I announced the top quark discovery March, 1995. • This discovery did not “just happen”: • Other experiments had been looking for the previous 20 years with no (real) top quark discovery. • PETRA (DESY): e+e- • SppS (CERN): p p • LEP I (CERN): e+e- • Run I was in its fourth year (after three years of Run 0 and many years of designing, building, and commissioning the detectors). TOP TURNS TEN TOP TURNS FOURTEEN SLAC HEP Seminar, March 5th 2009

  7. A Quick Note About Scale Cross Sections at Ös = 1.96 TeV For those not intimately familiar with Tevatron high pT Physics: Top: 1 in 10 Billion Reducingandunderstanding backgrounds is the key. 0.4 SLAC HEP Seminar, March 5th 2009

  8. Top Quark Review • Top: the Golden quark ( ~ 175 GeV/c2) • Only fermion with mass near EW scale. • 40 times heavier than the bottom quark. • Very wide (1.5 GeV/c2) • The top quarks decay before they can hadronize. • We can study the decay of the bare quark. • Usually observed in pairs. • Fundamental question: Is it the truth, the Standard Model (SM) truth, and nothing but the truth? • Did we really find the top quark? • Is it the SM top quark? • Is it only the SM top quark? • The top quark is an ideal place to look for Beyond the Standard Model Physics! - tt Pair Lepton + Jets Decay _ SLAC HEP Seminar, March 5th 2009

  9. New Era of Top Precision Physics! • CDF now have more than forty (40 !!!) times as much integrated luminosity as we did when we discovered the top quark in Run I! • With the data we have recorded, we are now able to have large, very pure top samples. • Of the almost 50 results that CDF sent to the summer conferences, more than half were in top physics! Double B-Tag W + Jets Candidates SLAC HEP Seminar, March 5th 2009

  10. What Can We Study About Top Quarks? _ Top physics is very rich. Branching ratios Rare decays Non-SM decays Decay kinematics W helicity |Vtb| Production cross section Production mechanism Resonance production Production kinematics Spin polarization Top charge Top spin Top mass Top width In today’s talk. Public CDF analyses. SLAC HEP Seminar, March 5th 2009

  11. Top Pair Decay Modes • According to the SM, top quarks almost (?) always decay to Wb. • When classifying the decay modes, we use the W decay modes: • Leptonic • Light leptons (e or ) • Tauonic () • Hadrons SLAC HEP Seminar, March 5th 2009

  12. The CDF II Detector Central Muon Detector Hadronic Wall Calorimeter Central Calorimeter (Em/Had) Plug Calorimeter (Em/Had) Solenoid Magnet Forward Muon Detector Protons Antiprotons y z x Luminosity Monitor [CDF] Central Outer Tracker Silicon Vertex Detectors SLAC HEP Seminar, March 5th 2009

  13. Important Tool: Particle ID • For many analyses, we need a very pure set of high pT electrons and muons. • Electrons (as we reconstruct them): • Have charged particle track. • Leave almost all of their energy in the electromagnetic calorimeter. • Ask for no other nearby tracks. • We do not want leptons from (heavy flavor) jets. • Muons: • Have charged particle track. • ~ Minimum ionizing (leave little energy in either the electromagnetic or hadronic calorimeter) • Find a “stub” of a track in dedicated muon detector systems on outside of CDF. • Ask for no other nearby tracks. K§, SLAC HEP Seminar, March 5th 2009

  14. Important Tool: Jet Reconstruction • We think of partons, but we reconstruct jets. • We need to convert “raw” jets to “corrected” jets - Jet Energy Scale (JES) correction. • Takes into account detector effects, neutral particles in jets, particles outside of the jet cone, underlying events, multiple interactions, … SLAC HEP Seminar, March 5th 2009

  15. Important Tool: . • Unlike e+ e- colliders, we don’t know what hit what. • We don’t know pz of the collision. • We do know px and py Use “transverse missing energy” ( or MET). • General idea: • Add up all (vector) energy in the XY plane, both “clustered” (part of reconstructed jets, leptons, etc.) and “unclustered.” • Reality: • Need to take into account jet corrections, muons, underlying events, extra interactions (pileup), … Close-up View of Layer 00 Silicon Detector Muon SLAC HEP Seminar, March 5th 2009

  16. Important Tool: B Jet Tagging • Since we (often) expect t  W b, b jet tagging is a very important tool. • Most backgrounds do not have bottom quark jets. • We rely on the long b quark lifetime. • B hadrons can travel several millimeters before decaying. • Use displaced vertices or many displaced tracks (impact parameter). Close-up View of Layer 00 Silicon Detector b-tag 2.4 cm b-tag jet jet SLAC HEP Seminar, March 5th 2009

  17. Top Physics Finally Makes Prime Time The Big Bang Theory! Mondays on CBS. Top Branching Fractions Top FCNC SLAC HEP Seminar, March 5th 2009

  18. Studying Pairs of Tops SLAC HEP Seminar, March 5th 2009

  19. Outline The Tevatron Top Quark Physics and CDF Top Pair Cross Section Top Quark Mass Single Top Cross Section Top Quark Properties Summary SLAC HEP Seminar, March 5th 2009

  20. Top Pair Cross Section Measurements • Why measure cross section? • Theory has precise estimate(s - see next slide). • New physics will affect different modes differently. • E.g., t ! H+ b, H+! decay is not equally well reconstructed in all decay modes. • Important to check assumptions and tools • With b tagging, using neural net, etc. • Need to understand sample composition for properties measurements. • Cross section formula: • Where: • - number of observed events, - background estimate. • - geometric acceptance, reconstruction efficiencies (e.g., lepton ID, b-tagging), and relevant branching fractions (e.g., W decays). • - integrated luminosity. SLAC HEP Seminar, March 5th 2009

  21. Theoretical Top Pair Cross Section • Easy Question: What is the theory cross section for top pair production at the Tevatron (√s = 1.96 TeV)? • Not-as-easy Answer: Depends on (in descending order of importance): • Top mass. • NLO vs NNLO parton distribution functions (PDF). • Who you ask. • NLO PDF and 175 GeV top mass: 6.7 pb. • World average top mass !172.5 GeV )+0.5 to +0.6 pb. • NLO !NNLO PDF: )+0.2 to +0.3 pb. • Cacciari et al.!Kidonakis and Vogt: )+0.1 pb. SLAC HEP Seminar, March 5th 2009

  22. “Lepton + Jets” + B-Tag Cross Section • Start with well – identified lepton and transverse missing energy consistent with a leptonic W decay. • Sample now dominated by W + associated jet production. • Other backgrounds “under control.” • Idea: • Look at each “jet bin” separately. • Take out all “understood” backgrounds (including top pair events). • What’s left is all W + jets events. • Use this to predict how many will have an identified B jet. • Sounds easy enough… • Reality: • W + heavy flavor jets are a small fraction, but very important in tagged analysis. ) Use W + 1 and 2 jet bins in data to measure. • All jets (fake lepton) difficult to estimate in MC ) Use data to measure SLAC HEP Seminar, March 5th 2009

  23. The Pieces • “Simple” b-tagging is not enough ) NN “flavor separator” • Use data in W + 1 jet and 2 jet bins. ) Measure: • W + bottom, W + charm, W + light flavor content. • QCD (fake) background is very difficult to model using MC. • We use “anti-electron” events. • Objects that are “electron-like” but do not meet at least two specific criteria • No real lepton ) No real . • Fit distributions. SLAC HEP Seminar, March 5th 2009

  24. “Lepton + Jets” B-Tagged Results SLAC HEP Seminar, March 5th 2009

  25. Outline The Tevatron Top Quark Physics and CDF Top Pair Cross Section Top Quark Mass Single Top Cross Section Top Quark Properties Summary SLAC HEP Seminar, March 5th 2009

  26. Why Measure Top Mass • Fundamental “parameter” in Standard Model. • Almost all SM predictions of top quark properties depend on top mass. • Coupled with W and Higgs masses. • Is the SM self-consistent? SLAC HEP Seminar, March 5th 2009

  27. Top Mass History SLAC HEP Seminar, March 5th 2009

  28. Lepton + Jets Top Mass • “Simple” top mass • Use same selection as Lepton + Jets b-tagged cross section • Use 2 fitter to reconstruct top mass: • Loop over many permutations – take best 2. • Make templates. • Create likelihood and fit for top mass. • Note that jet resolution or jet energy scale (JES) is a very big issue. Object Resolution Unclustered Energy Constraints W mass constraints Top mass “constraints” SLAC HEP Seminar, March 5th 2009

  29. Reducing Jet Energy Scale Uncertainties • In many of our decay modes (e.g., lepton + jets, all-hadronic), we reconstruct W bosons as two jets. • Since we know the true W mass, we can use this as an “in-situ calibration” of our JES systematic uncertainty. • Likelihood now depends on both top mass and JES. SLAC HEP Seminar, March 5th 2009

  30. Template Mass Results SLAC HEP Seminar, March 5th 2009

  31. Matrix Element Techniques • Basic idea: Use Fermi’s Golden Rule: Reconstructed object - parton transfer functions Input 4 Vectors Matrix Element Integration over phase space Parton distribution functions Signal (mtop) Background SLAC HEP Seminar, March 5th 2009

  32. Matrix Element L+J Top Mass • Also uses • B-tagged lepton + jets selection • Includes likelihood cut. • 19 dimensional integration! • Includes angular uncertainty in jets. SLAC HEP Seminar, March 5th 2009

  33. Matrix Element L+J Top Mass Results • First ever single quark mass analysis to have better than 1% precision. SLAC HEP Seminar, March 5th 2009

  34. Studying Single Top SLAC HEP Seminar, March 5th 2009

  35. Outline The Tevatron Top Quark Physics and CDF Top Pair Cross Section Top Quark Mass Single Top Cross Section Top Quark Properties Summary SLAC HEP Seminar, March 5th 2009

  36. Why Single Top? • “The Tevatron found top quarks produced in pairs in Run I. Why bother looking for single top production?” • Top pair production is QCD. Single top production is electro-weak. • Direct measurement of Vtbwith no assumption of three generations. • Single top decay can look very similar to SM Higgs decay, but can have a larger cross section by an order of magnitude or more. • If we can’t find single top, would anybody believe we can find Higgs boson? • Single top is an important background to Higgs. t - Channel : 2 pb s - Channel : 1 pb SLAC HEP Seminar, March 5th 2009

  37. Predicted Event Yield Background uncertainty is much larger than expected signal.  Makes counting experiment impossible! CDF RunII Preliminary, L=2.7 fb-1Predicted Event Yield in W+2jets Top pairs “relatively easy” SLAC HEP Seminar, March 5th 2009

  38. Analysis Techniques For Single Top • CDF used four different analysis techniques: • Matrix Element method (similar to top mass) • Neural Network • Exploits correlations between variables • Boosted Decision Trees • Likelihood Ratio • Why four different analysis techniques: • Very complicated analyses: Cross checks are important. • Even though analyses use the same events, combination of these analyses can give us more sensitivity. SLAC HEP Seminar, March 5th 2009

  39. pb pb pb pb Latest CDF Results . Strong evidence at ~4 level Combination in Progress SLAC HEP Seminar, March 5th 2009

  40. Neuro-evolution optimization NEAT Way to Combine Single Top • In the process of updating combinations for latest single top analyses. ) • Input: Discriminant of each analysis for each event. • Evolve neural network (including binning) to combine multiple single top analyses. Neuro-evolution of augmenting topologies (“NEAT”). • Selected for “discovery potential,” not minimizing cross section uncertainty. • Exp. p-val.: 5.1σ (13% improvement) • Obs. p-val.: 3.7σ (9% improvement) • σ = 2.2 ± 0.7 pb • |Vtb| > 0.66 @ 95% CL. SLAC HEP Seminar, March 5th 2009

  41. Single Top Combination With AIB • AIB: Asymmetric Iterative BLUE: • BLUE – Best Linear Unbiased Estimator • Well known technique for combining correlated measurements. • Input: Measured cross section from each analysis • Generated correlated PEs and measured correlations. • AIB, by definition, has same central value as BLUE, and • Results: • p-Values • 4.7 expected • 3.7 observed • Compatibilities: • Three measurements: • 87% • SM expectation 2.864 pb: • 14.8% (< 1.1) CDF Run II Preliminary 2.2 fb-1 SLAC HEP Seminar, March 5th 2009

  42. Breaking News! CDF and DØ each announced 5  Observation of Single TopLast Night! SLAC HEP Seminar, March 5th 2009

  43. CDF’s Observation of Single Top SLAC HEP Seminar, March 5th 2009

  44. CDF Single Top, Continued SLAC HEP Seminar, March 5th 2009

  45. DØ’s Observation of Single Top SLAC HEP Seminar, March 5th 2009

  46. Outline The Tevatron Top Quark Physics and CDF Top Pair Cross Section Top Quark Mass Single Top Cross Section Top Quark Properties Summary SLAC HEP Seminar, March 5th 2009

  47. × × Forward-Backward Asymmetry In Top Production • Why do we expect an asymmetry? ) Interference between diagrams Positive Asymmetry Negative Asymmetry SLAC HEP Seminar, March 5th 2009

  48. Forward-Backward Asymmetry In Top Production • How do we measure it? • Use kinematic fitter to reconstruct top, anti-top event. • In tt frame: • Use Qlep¢  y as discriminating variable. • In pp frame: • Use - Qlep¢ cos(h). • Calculate Afb. _ _ SLAC HEP Seminar, March 5th 2009

  49. Forward-Backward Asymmetry In Top Production _ _ tt Frame pp Frame SLAC HEP Seminar, March 5th 2009

  50. It is the relative reconstruction efficiency  acceptance that determines the relative yield. • is the relative acceptance when one top decays to the Wb while the other decays to the new decay, XY. • is the relative acceptance when both top quarks decays to the new decay, XY. • Compare expected yield to observed number of candidate events. • Create Feldman-Cousins acceptance bands using number of observed events. • t ! Zc, t ! gc, t !c, t ! Invisible. Search for Invisible Top Decays • What do we mean by “invisible?” • Not (well) reconstructed as double b-tag lepton + jets. • What would happen if there were a large branching fraction to an invisible decay? For example, • Br (t !Invisible) = 10%? • Br (t ! Wb) = 90% • P (tt ! Wb Wb) = 81% • ) For a purely invisible decay, we should have an 19% deficit when we look at the L + J event yield for a given theoretical cross section. XY SLAC HEP Seminar, March 5th 2009

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