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Recent Top Quark and Electroweak Measurements from CDF: Constraining the Standard Model Higgs

Recent Top Quark and Electroweak Measurements from CDF: Constraining the Standard Model Higgs. Eva Halkiadakis Rutgers University March 16, 2007 IFAE Seminar Barcelona. The Standard Model. The Standard Model is a good “ theory”

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Recent Top Quark and Electroweak Measurements from CDF: Constraining the Standard Model Higgs

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  1. Recent Top Quarkand Electroweak Measurements from CDF:Constraining the Standard Model Higgs Eva Halkiadakis Rutgers University March 16, 2007 IFAE Seminar Barcelona

  2. The Standard Model The Standard Model is a good “theory” Experimentally verified its predictions to incredible precision Almost all particles predicted by SM have been found But it does not explain everything Riddle of masses Why is there a hierarchy of masses? Higgs not yet observed It is required by the Standard Model

  3. Mtop vs. MW Interactions with Higgs gives particles mass. Its mass is tied to Mtop and MW.

  4. Outline Motivation Fermilab Tevatron Top Physics Overview Top Pair Production: Is top produced as expected? Total Cross Section Ratio of gg/qqbar Top Pair Production Top Quark Mass Electroweak Physics New Measurement of W Mass New Higgs Mass Limits Summary

  5. Fermilab Tevatron Batavia, Illinois p p proton-anti-proton collisions √s = 1.96 TeV Discovered the top quark in 1995! Will run until 2009

  6. Top Quark Discovery Discovered by CDF and DØ in 1995 during Run I of Tevatron Top > 10 years old! Final Run I analyses ~110pb-1 ~30 events per experiment “Precision Era” in Run II Collected > 2 fb-1 > factor of 20 more data! Can only be studied at Tevatron until LHC turns on! Want lots of top events to study its properties!

  7. Integrated L Weekly record: 40 pb-1 /week/expt Total delivered: ~2.5 fb-1 /expt Total recorded: >2 fb-1 /expt Record peak L ~2.8x1032 cm-2s-1 Expect ~4fb-1 delivered by end of year! TeVatron and CDF Performance

  8. Why Is Top So Special? Quark Masses t b c s d u GeV/c2 • Top is MASSIVE! Mtop= 172.5  2.3 GeV (TEWG hep-ex/0603039) • Decays before hadronization! • top ~ 10-25 s,  ~ 1.5 GeV >> QCD ~200 MeV • Spin transferred to decay products • Special role in EWSB? • Top Yukawa coupling to Higgs is “natural” (~1) • Mtop together with MW constrains MHiggs • Probes physics at • much higher energy • scales than other • known fermions …. Log scale! 5 orders of magnitude between quark masses! Is there anything beyond the SM????

  9. Top Quark Pair Production TevatronLHC (ttbar) ~7 pb~830 pb qqbar ~85%~10% gg ~15%~90%

  10. Top Quark Decay Modes golden channel

  11. Typical Collisions Look Like This: Can YOU find the W boson, top quark, or even the Higgs?

  12. CDF Detector at FNAL

  13. Identifying Top • leptons (e,and) •  (missing ET) • quarks (jets) • b-quarks (“b-tag” jet)  b-tag b-tag = MET jet jet

  14. Physics With Top W helicity Branching ratios Rare decays Non-SM decays Decay kinematics |Vtb|  Production cross section Production process Resonance production Production kinematics Spin polarization SM top production?  Top charge Top spin Top lifetime Top mass  Anomalous couplings

  15. Is Top Produced As Expected? Measure the total cross section Test QCD in high Q2 regime Deviations from SM expectations could indicate non-SM productions mechanisms Or new physics in the top sample?

  16. Top Quark Samples For example, in 1 fb-1 of integrated luminosity: Branching Ratio + trigger 200 dilepton 1000 lepton + jets 2000 all-hadronic 7000 tt events produced event selection Main backgrounds W+jets, WW, WZ, DY mistag, W+hf, V V, non-W QCD multijets S/B ~ 2:1 S/B ~ 3:1 S/B ~ 1:5 50 dilepton 200 lepton + jets (with b-tag) 300 all-hadronic (with b-tag)

  17. Lepton + Jets Cross Section control L ~ 695 pb-1 ttbar l+jets 158 events  4 jets  1 b-tag signal

  18. Top Production Cross Section Measurements in all channels using different methods are found to be consistent. Ongoing effort to have a Tevatron combined average. Most precise single measurement ~14%! Tevatron Goal: 10% uncertainty/experiment with 2fb-1.

  19. Is Top Produced As Expected? How much vs. ? Measure ratio of gg/qq top pair production  Use the kinematics of the production and decay Test pQCD and sensitive to new physics 85% qq annihilation In qq annihilation events ttbar prefer to have like spin. 15% gg fusion In gg fusion events ttbar prefer to have unlike spin. Like Spin Unlike Spin

  20. Top Pair Production Mechanism L ~ 695 pb-1 ttbar l+jets 167 events  4 jets  1 b-tag Herwig MC Analysis Strategy Use an Artificial Neural Network (NN) 8 input variables (production + decay) top velocity and production angle 6 decay angles NN trained to distinguish ttbar gg events from a sample of gg+qq ttbar events cosθ* in ttbar rest frame, angle between the top and the right incoming parton Make templates of the “probability” (output of NN) of the event to be gg produced Minimize likelihood Two signal terms (qq/gg production) Background term

  21. Top Pair Production Mechanism We fit for gg fraction of ttbar events. We ensure a physical result by using Feldman-Cousins Method. True gg Fraction Result: 68% C.L.: < 23% 95% C.L.: < 51% Fitted gg Fraction

  22. Top Quark Mass Now we believe what we see is top, let’s measure it’s properties: Top quark mass! How? Each event has 2 top quarks Two chances to measure its mass in each event Ideally: We don’t live in an ideal world….

  23. Measuring Mtop is Challenging! • Combinatorics: • Experimental observations are not as pretty as Feynman diagrams! • Which jets go with which quarks? Final State from Leading Order Diagram What we measure

  24. Measuring Mtop is Challenging! • Determine true “parton” energy from measured jet energy in a cone Jet energy scale (JES) Determine the energy of the quarks produced in the hard scatter We use the Monte Carlo and data to derive the JES Jet energy scale uncertainties Remaining differences between data and Monte Carlo from all these effects JES has historically been dominant systematic for Mtop!

  25. Jet Energy Scale Uncertainty About 3% of Mtop when convoluted with ttbar pT spectrum

  26. Handles On Measuring Mtop b-tagging Reduces combinatorial and physics backgrounds In-situ JES calibration Use Wjj mass to measure JES uncertainty Scales directly with statistics! Constrain the invariant mass of the non-b-tagged jets to be 80.4 GeV/c2 Mjj

  27. Mtop Measurements At The Tevatron Robust program of top quark mass measurements Many measurements in all the different channels  consistency Different methods of extraction with different sensitivity  confidence Combine all channels and all methods precision As I cannot cover them all, I will present the most precise.

  28. Matrix Element Analysis Technique Experiment Signal event Background event Signal event = Signal event = Signal event X X Background event Experiment CDF adaptation of method used by D0 in Run I Nature Vol 429, June 2004 Optimizes the use of kinematic and dynamic information Build a probability for a signal and background hypothesis Likelihood simultaneously determines Mtop, JES, and signal fraction, Cs:

  29. Matrix Element Analysis Technique W(x,y) is the probability that a parton level set of variables y will be measured as a set of variables x (parton level corrections) dnis the differential cross section: LO Matrix element For a set of measured variables x: JES sensitivity comes from W resonance All permutations and neutrino solutions are taken into account Lepton momenta and all angles are considered well measured Background probability is similar, no dependence on Mtop f(q) is the probability distribution than a parton will have a momentum q

  30. Mtop Results L ~ 940 pb-1 ttbar l+jets 166 events exactly = 4 jets,  1 b-tag World’s most precise measurement!

  31. Future of Mtop @ CDF We surpassed our Run II goal of measuring to 3 GeV/c2 precision Have made extrapolations based on present methods Upper limit: Only (stat) improves with luminosity Lower limit: Everything improves with luminosity Reality: likely somewhere in between With full Run-II dataset CDF should measure Mtop to < 1%

  32. The Other Axis: Measuring MW From the Tevatron: δMtop = 2.1 GeV => δMH / MH = 18% Equivalent δMW = 12 MeV for the same Higgs mass constraint “Old” world average δMW = 29 MeV progress on δMW now has the biggest impact on Higgs constraint!

  33. W and Z Production Number of candidates in ~200pb-1 : ~64000 W  e ~51000 W   ~2900 Z  ee ~4900 Z   Isolated, high pT leptons Missing transverse momentum in W's Z events provide excellent control sample Typically small hadronic (jet) activity

  34. W Mass Measurement W mass information contained in location of transverse Jacobian edge Provides cross-check of production model. Needs theoretical model of pT(W) Provides cross-check of hadronic modelling Insensitive to pT(W) to first order. Reconstruction of pTν sensitive to hadronic response and multiple interactions

  35. W Mass Measurement Quark-antiquark annihilation dominates (80%) Precise charged lepton measurement is the key (achieved ET precision ~0.03%) Recoil measurement allows inference of neutrino ET . Require small recoil U<15 GeV Use Z and Zee events to derive recoil model

  36. W Mass Measurement Strategy W mass is extracted from transverse mass, transverse momentum and transverse missing energy distribution Fast Simulation NLO event generator Model detector effects W Mass templates Detector Calibration 81 GeV Tracking momentum scale Calorimeter energy scale Recoil 80 GeV Data + Backgrounds Binned likelihood fit W Mass

  37. Detector Calibration: Lepton Energy Scale Energy scale measurements drive the W mass measurement Calibrate lepton track momentum with mass measurements of J/and  decays to  Calibrate calorimeter energy using track momentum of e from W decays Cross­check with Z mass measurement, then add Z's as a calibration point Z  ee Z  

  38. Detector Calibration: Recoil Calibrate recoil measurement with Z decays to e,  Cross­check with W recoil distributions W  e W  

  39. Transverse Mass Fits Mass fit results blinded with 100 MeV offset throughout analysis Upon completion, offset removed to determine final result W   W  e MW = 80417 ± 48 MeV (stat + syst) Electron+Muon combination yields P(2) = 7%

  40. Additional W Mass Fits Also fit ET and missing ET distributions in muon and electron channels and combine with transverse mass fits: W  e Electron ET MW = 80413 ± 48 MeV (stat + syst) Combination of all six fits yields P(2) = 44% W   Missing ET

  41. W Mass Systematics Systematic uncertainty on transverse mass fit Combined Uncertainty: 48 MeV for 200 pb-1

  42. W Mass Results New CDF result is the world’s most precise single measurement World average increases: 80392 to 80398 MeV Uncertainty reduced ~15% (29 to 25 MeV)

  43. Future of MW @ CDF Projection from previous Tevatron measurements Expect MW < 25 MeV with 1.5 fb-1 already collected

  44. Higgs Mass Limits Previous SM Higgs fit (LEPEWWG) : MH = 85 +39-28 GeV MH < 166 GeV @ 95 C.L. MH < 199 GeV @ 95 C.L. Including LEPII direct exclusion Updated preliminary SM Higgs fit (M. Grunewald, private communication): MH = 80 +36-26 GeV MH < 153 GeV @ 95 C.L. MH < 189 GeV @ 95 C.L. Including LEPII direct exclusion

  45. Summary We’ve come a long way since the top quark discovery! Entered precision era! We have 2fb-1 of data on tape and counting! Best Mtop measurement in the world @ CDF Surpassed our Run II goal. Should reach 1% precision with full Run-II data set. World’s most precise single measurement of MW Should measure to <25MeV with 2fb-1 The top/electroweak sector is a thriving field with an exciting future at the Tevatron. Until the discovery of the Higgs, we will continue to squeeze the SM by making high precision measurements. Helps us prepare for challenges of physics measurements ahead at the LHC!

  46. Backup

  47. Electroweak Fits

  48. SM Higgs at the Tevatron

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