The truth about the top quark from CDF

The “truth” about the “top” quark from CDF Véronique Boisvert University of Rochester Royal Holloway University of London CERN seminar February 19 th 2008 1

The Standard Model 2

What we don’t know… Ø Incorporate neutrino mass in the SM in a natural way Ø Strong CP problem: Why QCD does not break CP? l Electric dipole of the neutron: -16 QCD e cm d. N~5 x 10 • d. N< 3. 0 x 10 -26 e cm so QCD < 10 -10 • naturalness: QCD O(1) so fine tuning Higgs mass should be around 1016 Ge. V, not O(100 Ge. V) Ø Planck scale so different from the Electroweak scale Ø Hierarchy Problem 3

What we don’t know… 4

Higgs Mass Electroweak observables put strong constraints on the Higgs mass Ø Higgs enters into radiative corrections of EW boson Ø l l Ø Only logarithmically Top mass enters quadratically… Higgs largest coupling is to the top quark 5

Ø … Top mass is so large…Maybe the Top quark is not just a normal quark… maybe it’s involved more directly in the electroweak symmetry breaking mechanism! 6

An Example of this… Ø “Little Higgs” models l Similarly to SUSY predict new particles to cancel Higgs mass divergences • Fermions cancel fermions and bosons cancel bosons • “nonlinearly realized symmetry” l Predictions: • One or several Higgs with relatively small masses • At least one heavy fermion (T) m < 2 Te. V to cancel the top • New heavy gauge bosons (Z’) l Signatures in Tevatron top quark sector: • Z’ forward-backward asymmetry to tt pair 7

So far… Ø Looked at Standard Model l Hierarchy problem • Electroweak symmetry breaking mechanism is involved • Top quark seems to be an important player and could give us clues Ø Top l l l Physics: Next… Top Factory: Tevatron Top Production Top measurements 8

Current Top Factory: Tevatron Ø World’s highest energy collider (until this summer…) l Ø Run I (1992 -1996) l l l Ø √s = 1. 8 Te. V 6 x 6 bunches, 3 s spacing 100 pb-1 int. luminosity Upgrades to the accelerator: l l Ø Proton-antiproton Synchrotron Main injector Pbar recycler/e-cooling Run II (2001 -2009) l l √s = 1. 96 Te. V © J. 396 ns Lück spacing 36 x 36 bunches, 9

Tevatron Performance Ø Record Luminosity achieved for a hadron collider: l ~2. 86 E 32 cm-2 s-1 Design 1500 pb-1 2007 Base 750 pb-1 2006 Ø 2005 2004 2003 Fiscal Years Expect 6 -7 fb-1 by October 2009 3. 2 fb-1 delivered 2. 7 fb-1 on tape 80 -90% Operating Efficiency 10

Collider Detector at Fermilab Comparison of CDF with ATLAS Electron of 100 Ge. V and hadron of 100 Ge. V CDF: (ECAL)~ 2. 0% (HCAL)~8% ATLAS: (ECAL)~1. 2% (HCAL)~5. 8% Drift. Calorimeter chamber outer tracker: showers much better defined with ATLAS Example of consequence for top physics: Probability of. Silicon jet faking an electron vertex detector: is much reduced at ATLAS (IP)~40 m, (z(less coverage--out to | |<2. 8 QCDtracking background reason 1) 0)~ 70 m, Central calorimeter: Plug calorimeter: coverage out to | |<3. 0 Muon chambers: coverage out to | |<1. 0 11

Collider Detector at Fermilab 2. 5 MHz ØChallenges L 1 Trigger 20 k. Hz L 2 Trigger at high L: Trigger rates out of control (L 1, L 2) l. So high dead time l. Processing time (L 3) l. Data size & transport l 600 Hz L 3 Trigger 90 Hz Muon Extension Trigger Cross-Section (nb) 20 MB/s Offline Reconstruction Simulation 1 PB/yr physics cross-section! Data Handling 12

Silicon detector Ø One of the biggest silicon detectors currently online l Ø (722 K channels, 6. 2 m 2) Cannot be accessed for maintenance l l l ‘space probe’ engineering and operation Needs to ‘live’ longer than designed for 1. 35 cm away from the beam • improved performance • a dangerous place to be Silicon hits-on-track efficiency 94. 8% if requiring 3 r-f layer hits Ø 9 m resolution for residuals Ø The key to top and B physics Ø 13

The Standard Model Top CDF Ø Top quark is isospin partner of b quark: l l l Ø Charge = +2/3 Spin = 1/2 Mass = ? ? ? How is top produced: l inel=70 mb so 7 M events/s at 1032/cm 2 s but 1 tt in 1010 events Less QCD bckgd -reason 2 Tevatron: • qq vs gg is 85% vs 15% • For mt=175 Ge. V/c 2: l ATLAS tt (theo) 6. 7± 0. 8 pb • top are nearly at rest l Pythia Herwig LHC: Pythia tt • qq vs gg is ~10% vs 90% • For mt=175 Ge. V/c 2: l NLO tt (theo) 830± 100 pb • more momentum available HEPG-level PT of ttbar (Ge. V) 14

Single Top Production Ø LHC Electroweak production: Ø Different New Physics l l s-channel: New resonances t-channel: FCNC =60 pb Measurement of |Vtb| if assume SM Ø Anomalous Wtb coupling Ø CP violation: Ø s-channel t-channel s=10 pb LHC s=0. 88 0. 07 pb s=250 pb LHC t=1. 98 0. 21 pb 15

Standard Model Top mt>m. W+mb so dominant decay t Wb Ø If assume unitarity B(t Wb)~100% Ø Top decays before it feels non-perturbative strong interaction l. Can study the bare quark (eg spin) l No top-hadrons or tt-quarkonium l Top spin transferred to decay products l 16

Studying the top quark Top Mass W helicity Top Width Production cross-section Resonance production Top Lifetime Anomalous Couplings W+ CP violation Top Charge p t, t’ Production kinematics Top Spin Polarization l+ Top Spin b X _ _ p t Rare/non SM Decays _ b q W- _ q’ Branching Ratios |Vtb| 17

Next Ø Top pair cross section measurements • Dilepton • Lepton + Jets • All hadronic Ø Measuring tt is crucial: l l l Window to NP Look at all possible channels Starting point for most properties analysis • Literally… selection is the same so can use same acceptance scale factors and same background predictions l tt is background for searches 18

Triggers used by Top group Ø Physics triggers ØELECTRON_CENTRAL_18 L 1_CEM 8_PT 8 l. L 2_CEM 16_PT 8 l. L 3_ELECTRON_CENTRAL_18 l ØMUON_CMUP 18_L 2_PT 15 L 1_CMUP 6_PT 4 l. L 2_CMUP 6_PT 15 (was L 2_CMUP 6_PT 8) l. L 3_MUON_CMUP_18 l Analysis requirements For lepton p. T: > 20 Ge. V Calibration triggers (prescaled!!): • Example of trigger efficiencies: l ~ 14 ØMUON_CMX 18_L 2_PT 15 • Tag & Probe using Z’s l Monitoring l. L 1_CMX 6_PT 8_CSX Recently • Tracking: l b-tagging: 0. 9838(3) dep. ) l. L 2_CMX 6_PT 15 • • L 1: Prescaling is part( of the statistical prescaled uncertainty of b-tagging efficiency • L 2: 0. 9993(1) (was L 2_CMX 6_PT 10) b-tagging efficiency is among • L 3: 0. 9966(2) dominant systematics of l. L 3_MUON_CMX_18 analyses using b-tagging • Calorimetry: ØTOP_MULTI_JET • L 1: 100% • L 2: ET dep. • L 1_JET 10 • L 3: 100% l. L 2_FOUR_JET 15_SUMET 175 all hadronic channel • Total for top analyses: (was SUMET 125) b tagging matrix • Dilepton: mistag 0. 9772(44) 19 l. L 3_FOUR_JET 10 • L+J: 0. 9755(55) Ø l

Cross section in dilepton channel Ø Event Selection: l 2 leptons ET>20 Ge. V with opposite sign l ≥ 2 jets ET>15 Ge. V l Missing ET >25 Ge. V (and away from any jet) l Ø HT=p. Tlep+ETjets+MET>200 Ge. V Backrounds: l Drell-Yan: • Large • Must have “fake” MET • Estimate from data l W+jets: • Large • Must have jet faking lepton • Estimate from data l Diboson (WW, ZZ, …) • Small • Estimate from MC 20

Cross section in dilepton channel X = DY prediction MC data X N(W+jets)data = Fakes prediction 21

Cross section in dilepton channel s(tt) = 6. 2 ± 1. 1 (stat) ± 0. 7 (syst) ± 0. 4 (lumi) pb 22

That number is actually… Dozen numbers for a given electron and muon selection 23

Cross section in L+J channel Ø Event selection: l 1 lepton ET>20 Ge. V l ≥ 3 jets ET>15 Ge. V l l l Missing ET >20 Ge. V HT=p. Tlep+ETjets+MET>200 Ge. V ≥ 1 jet: secondary vertex tag with significant positive decay length Ø Backgrounds: l W+jets • Use data and MC l QCD • Use data 24

b tagging in top events Ø b hadrons are massive: l l Tagging eff per Top evt: 15% Transition into lighter flavors Semileptonic decay: 20% Mistag rate: 3. 6% • Soft Lepton Tag Ø b hadrons have life time: l l ct~460 m, travel few mm Make secondary vertex • Sec. Vtx tagger 44% 25

b tagging in Top events B-jet Jet 3 Jet 4 26

Cross section in L+J channel s(tt) = 8. 2 ± 0. 5 (stat) ± 0. 8 (syst) ± 0. 5 (lum) pb 2 b tags 1 b tag s(tt) = 8. 8 ± 0. 8 (stat) ± 1. 2 (syst) ± 0. 5 (lum) pb 27

Cross section in all hadronic Ø Selection: l l 6 N jets 8 with p. T>15 Ge. V/c DRmin 0. 5 1 b tagged NN discriminant > 0. 94 Ø discriminate Huge QCD background ! 11 kinematic variables in neural net 28

Summary of Top cross sections Ø Can already test theory estimate Ø Soon can test among different channels 29

Ø Looked l So far… at Standard Model Hierarchy problem • Electroweak symmetry breaking mechanism is involved • Top quark seems to be an important player and could give us clues Ø Top l l Physics: Top Factory: Tevatron Top Production Top cross section measurement Top properties measurements 30

Top Mass W helicity Top Width Production cross-section Resonance production Top Lifetime Anomalous Couplings W+ CP violation Top Charge p t, t’ Production kinematics Top Spin Polarization l+ Top Spin b X _ _ p t Rare/non SM Decays _ b q W- _ q’ Branching Ratios |Vtb| All CDF Top results: http: //www-cdf. fnal. gov/physics/new/top. html 31

Why Measure Top Charge “Top” is SM Top (Q=+2/3) or something more exotic related with EWSB? Ø Alternative to +2/3 Ø l l (Q 1, Q 4)R Q 4 q=-4/3 Better global EW fit • gb. L shift: larger mt • gb. R shift: mixing of b. R with (Q 1, Q 4)R l l l 2. 5 s deviation mt~274 Ge. V/c 2 Higgs triplet D. Chang et. al. Phys. Rev. D (59) 1999 091503 Choudhury, Tait, Wagner, PRD 65, 053002 (2002) 32

How to measure the |charge| X W+b or W-b (and cc)? Ø Ingredients: Ø l ? 1) Charge of W • Charge of lepton l l Ø 2) Pairing between W and b 3) Flavor of b jet Datasets: l ? ? Use cross section meas. • Dilepton (single tagged) • Lepton+Jets (double tagged) b or b ? 33

Wb pairing Ø Dilepton Channel: l l l Calculate Mlb 2, order 4 values in ascending order Mlbmax 2 > 21, 000 Ge. V 2/c 4 Choose combination without Mlbmax 2 L 1 b 1 =39% P=95% D 2=0. 32 L 2 b 2 D=2 P-1 Ø Lepton+Jets Channel: Constraints: W mass, top mass, etc. l l l Same 2 as in top mass analyses 12 combinations x 2 (pz neutrino) l Double tagged events: • 4 combinations l Take min 2 combination and require < 9 e=53% P=86% e. D 2=0. 27 34

Top Mass 2 UE=Unconstrained Energy (energy outside tt interaction) Ø Fit modifies pt of leptons and jets Ø l l Improves resolution Improves probability of correct assignment Constrained or unconstrained fit Ø 24 possible combinations (2 pz possible) Ø Ø Performance of correct b assignment: l l (take lowest 2 combination) 1 “tight” b-tag constrained fit: 60% 2 “loose” b-tag constrained fit require lowest 2 < 9: 84% 35

b flavor tagging Dil: e=87% P=61% e. D 2=0. 10 L+J: e=98% P=61% e. D 2=0. 13 Ø Need to calibrate in data! Compare: Jet. Q(away jet) vs Q( ) PTrel Soft Jet axis x b tagged B 0 pbd duu b Correct for: b c x Mixing Away Jet b tagged Need to obtain non-b fraction: Use PTrel fit Extrapolate to high p. T, Use Away Jet Mvtx SF=1. 01 ± 0. 01(stat) ± 0. 02(syst) 36

Statistical treatment From Data N(SM), N(XM) then what? Ø Use Profile Likelihood method where ƒ+ is parameter of interest Ø l Get p-value according to SM • Prob of measuring ƒ+ <= value l Decide before looking at the data a value of =1% • =Prob of incorrectly rejecting the SM • =sensitivity= prob of rejecting the SM if XM is true = 87% Ø Since comparing 2 hypothesis (SM vs XM) compute a Bayes Factor: l l Ø Likelihood ratio and integrate over the nuisance parameters If use expectations get x+=102 out of 179 : 2 Ln(BF)=13. 1 ~ 3. 6 Also provide Feldman-Cousins bands for ƒ+ XM SM ƒ+ If p-valuedata>0. 01: exclude XM at 87% confidence If p-valuedata<0. 01: exclude SM at 99% confidence 37

Data Results Using 124 SM and 101 XM Ø Get ƒ+ = 0. 87 Ø p-value=0. 31 Ø Since this is >0. 01 Ø l Ø We exclude the XM with 87% confidence Bayes Factor is 12. 01~3. 4 l The data favors “very strongly” the SM over the XM 38

Feldman-Cousins band Ø +> 0. 40 at 95%CL 0. 46 at 90%CL Ø +> 0. 60 at 68%CL 39

W helicity measurement Ø Measurement possible because of large Top mass l Ø Top spin transferred to decay products Test V-A structure of the t. Wb vertex l EWSB predicts large longitudinal component: • At LO: 40

W helicity measurement Need to correct for acceptance effects! Ø Choose 3 analyses: l 2 involving cos * • Unfolding method • Template method l 1 making use of Matrix Element 41

Unfolding method results • Unfolding method Use MET for the neutrino four-momentum • • Fully reconstruct the tt event Calculate cos * Construct efficiency and migration matrix Fit helicity fractions using binned likelihood fitter Ambiguity for pz Try all possible hypothesis of assigning jets to partons • Build a quantity for each hypothesis: • P is a weighting factor for the chosen z component solution of the neutrino • Pb-light is measure of light quark likeness • 2 is constraint on mass of W, top and total transverse energy of the event 2 -D fit: Unfold cos * distribution 42

Unfolding method results Unfolding method Fully reconstruct the tt event Calculate cos * Construct efficiency and migration matrix Fit helicity fractions using binned likelihood fitter 2 -D fit: 1 -D fits: 43

Unfolding method results Unfolding method Fully reconstruct the tt event Calculate cos * Construct efficiency and migration matrix Fit helicity fractions using binned likelihood fitter Unfold cos * distribution 44

Template method results Template method Fully reconstruct the tt event Calculate cos * Construct templates for +, -, 0 W’s and background Fit helicity fractions using unbinned likelihood fitter Correct for acceptance effects 45

Template method results Template method Fully reconstruct the tt event Calculate cos * Construct templates for +, -, 0 W’s and background Fit helicity fractions using unbinned likelihood fitter Correct for acceptance effects 46

Template method results Template method Fully reconstruct the tt event Calculate cos * Construct templates for +, -, 0 W’s and background Fit helicity fractions using unbinned likelihood fitter Correct for acceptance effects 2 -D fit: 1 -D fits: 47

Matrix Element method Ø Obtain Likelihood for N events: Minimize Cs (tt fraction) using Minuit at each 0, obtain: -ln. L(X; 0) curve Ø Signal acceptance vs 0 l Analytical parameterization Ø 48

Matrix Element Method Ø Calibration: Pseudoexp and input vs 0 output l Slope < 1: • Eg NLO effects l Pull width vs 0 • Average is 0. 93 • Independent of 0 • Scale statistical uncertainty by 0. 93 Ø Results: 49

Summary of W helicity results + M 2 lb(0. 75 fb-1) 0 ME(1. 9 fb-1) Template 1 d (1. 9 fb-1) Template 2 d (1. 9 fb-1) Unfolding 1 d (1. 9 fb-1) Unfolding 2 d (1. 9 fb-1) 50

tt Front Back Asymmetry Ø First measurement of discrete symmetries of the strong interaction at high energies! l Tevatron favored over LHC for this (qq vs gg production) NLO QCD predicts overall charge asymmetry Not expected for strong interactions 4 -5% Kuhn-Rodrigo, 3. 8% MC@NLO But new productions mechanisms (Z’, top color) could appear as front back A 51

tt Front Back Asymmetry Ø Reconstruct production angle: l Ø Assign parton to jets using the top mass 2 Need to correct for: l Backgrounds: • Subtract bin by bin l Check shape running on data anti-tag sample • Afbbckd=-0. 5± 0. 01 (W+jets) l Reconstruction (mismeasured jet E, etc. ) and Acceptance (detection efficiencies) • Matrix inversion using MC 52

tt Front Back Asymmetry Ø Underlying distribution might look different from MC l Ø High number of bins (4) in matrix inversion take care of this Corrected Result: l l Afb=0. 17± 0. 07(stat)± 0. 04(syst) vs Afb. Theo=0. 04± 0. 01 53

tt Front Back Asymmetry Ø 2 nd analysis: l l Parton rest frame using A(parton rest frame) = 1. 3 A(lab frame) l Corrected Inclusive result: • Afb=0. 24± 0. 13(stat)± 0. 04(syst) • vs Atheofb=0. 06± 0. 01 54

Flavor Changing Neutral Currents Ø In the SM no FCNC at tree level l Need loop diagrams • B(t Zq)=O(10 -14) Ø New Physics enhances that BF l Ø Previous searches: l l l Ø Observation = New Physics! CDF Run I: B(t Zq)<33% at 95%CL L 3: B(t Zq)<13. 7% at 95%CL (HERA most sensitive to t (u, c) vertex) [after J. A. Aguilar-Saavedra, Acta Phys. Polor B 35 (2004) 2695] Perform analysis using 1. 9 fb-1 tt Wb Zq l l W qq and Z ll (4%) (Z+4 jets) Background is mostly Z+jets! 55

FCNC Event Selection Two quark jets form W boson Jet from b quark, can be combined with W to form top quark Additional jet, can be combined with leptons to form top quark l Divide sample into • Control (1 cut failed) • 0 b-tag (anti-tagged) • 1 loose b-tag (tagged) Two leptons (ee or µµ) with opposite charge, form Z boson 56

FCNC Ø Event selection: l l Ø Transverse mass: top more central than Z+jets Strongest discriminant: It’s all about backgrounds: l l l Z+jets: data and MC tt : rely on pythia and measured WZ, ZZ: rely on pythia 57

FCNC Z+jets: template fit to the data in control region and 2 signal regions Ø Diboson and tt are fixed (small) Ø Fit returns Ø l Z+jet and signal amounts • Shape is changed according to best fit of Jet Energy Scale l Ø Tagging rate Use MC for estimate of fraction of Z+jets in control region vs in signal regions l 20% uncertainty 58

FCNC Ø Feldman-Cousins limit obtained using full systematic studies l l B(t Zq)< 3. 7% at 95%CL 3. 5 times better than published best limit from L 3 (~10 x better than Run 1 results) 59

Top mass results 1. 9 fb-1 results presented at winter conferences! Lepton+Jets and Dilepton with in-situ JES calibration: (1. 1%) 171. 9 1. 7(stat+JES) 1. 0(syst) Ge. V/c 2 (1. 1%) 2. 2%! 60

Single top results D 0 paper: “Evidence for production of single top quarks”: PRL 98 181802 (2007) D 0’s paper: “Evidence for http: //www-cdf. fnal. gov/physics/new/top/public_singletop. html 61

The “truth” about the Top tt measurements consistent with SM Production cross-section Top Mass Top Width + l Anomalous consistent Top Spin with 0. 7 + consistent with 0 0 Top Lifetime W+ Top Charge AFB within 2 Resonance of SM value production W helicity Couplings CP violation p Charge -4/3 excluded ØNo hints of. Production New Physics in top sector… yet! t, t’ the b quark at 87% CL kinematics _ of final dataset! l. Only analyzed less than a third X Top Spin Polarization _ _ p t Rare/non SM Decays b q No hints of Flavor Changing W- Neutral Currents _ q’ Branching Ratios |Vtb| 62