Physics with Top Quarks Prof. Robin Erbacher University of California, Davis Lepton-Photon 2007

Something about top history Top Discovery! Tevatron Run 1 1994-5 R. Erbacher - LP07

Top Rediscovered in Run 2 R. Erbacher - LP07

Periodic Table of the Particles 5 orders of magnitude! R. Erbacher - LP07

New Physics?!? Many top properties measurements just beginning to have sensitivity: lots about top still to understand! R. Erbacher - LP07

Top physics is one of the more sexy things to study at the Tevatron… R. Erbacher - LP07

Top Event Decays Top Quark Production Top Properties W helicity (V-A) Branching ratios Top to charged higgs Top sample (W+c) FCNC Top Quark Production Mechanism Top Pair Cross Section Ewk Production (single top) Forward-backward asymmetry Resonances decaying to top stop production Top Properties Top Mass Top Quark Width Charge of Top Quark R. Erbacher - LP07

Events Characterized by W Decays tWb ~ 100% R. Erbacher - LP07

Dilepton Decay Mode R. Erbacher - LP07

Lepton+Jets Decays R. Erbacher - LP07

All-Hadronic Decays R. Erbacher - LP07

- Muon + jets event with 2 tagged b-quark jets Jet 2 Jet 1 MIP signal In calorimeter Jet 2 secondary vertex interaction point Jet 1 secondary vertex interaction point Muon + jets event with 2 tagged b-quark jets R. Erbacher - LP07

Strong Pair Production at the Tevatron How is top produced? ~85% Rarely!! Strong Pair Production at the Tevatron ~15% One top pair each 1010 inelastic collisions at s = 1.96 TeV R. Erbacher - LP07

Electroweak Single Top Production New Resonance Production? s-channel ~1 pb t-channel ~2 pb New Resonance Production? R. Erbacher - LP07

Fermilab, Chicago, IL U.S.A. Fermilab Tevatron Tevatron DØ CDF Chicago Booster Wrigley Field p source Main Injector Fermilab, Chicago, IL U.S.A. R. Erbacher - LP07

General purpose detectors capable of many different physics measurements Top physics uses almost all detector systems R. Erbacher - LP07

Top Quark Production Production mechanism Top pair cross section EWK production (single top) Forward-backward charge asymmetry Resonances decaying to top Search for stop production R. Erbacher - LP07

Does t-tbar production match NLO prediction? (ggtt)/(pptt) = 0.07 ± 0.16 (NLO: gluon~15%, quark~85%) (neural net analysis: fg < 0.33 @ 68% CL) R. Erbacher - LP07

(tt) = Luminosity *  Top Pair Production Cross Section: t-tbar! Nevents - Nbackground (tt) = Luminosity *  t-tbar! Top Pair Production Cross Section: As QCD predicts? Only SM top? By heavy particles? R. Erbacher - LP07

Event topology Discriminant: No b-jet Top pair tagging Requiring two tt=8.1 ± 0.9(stat)± 0.5(sys) pb Requiring two identified b-jets: Ultra pure top pair sample Lepton + Jets Top pair R. Erbacher - LP07 tt=8.2 ± 0.5(stat)± 0.9(sys) pb

Many new dilepton measurements! Dilepton Selection Cross Section (Mtop =175 GeV) 2 Tight Leptons (1.2 fb-1) tt= 6.2 ± 1.1(stat)± 0.7 (sys) pb Lepton+Track (1.1 fb-1) tt= 8.3 ± 1.3(stat)± 0.9 (sys) pb Lepton+Track+btag (1.0 fb-1) tt= 10.1 ± 1.8(stat)± 1.3(sys) pb 2 Tight Leptons (1.0 fb-1) tt= 6.8 ± 1.2(stat)± 0.9(sys) pb 2 T+ L+T+btag comb (1.0 fb-1) tt= 6.0 ± 0.9(stat)± 0.8(sys) pb Lepton+Tau+btag (1.0 fb-1) tt= 8.3 ± 1.9(stat)± 1.4 (sys) pb Many new dilepton measurements! Tau Lepton channels difficult! Expected xs*BR = 0.12 from theory *BR(ttl++2+2b) = 0.19±0.08(stat) ± 0.07(syst) pb ! R. Erbacher - LP07

background uncertainty! Single Top Production: Rate  |Vtb|2 in SM Sensitive to H+, 4th gen, W’, FCNC, … Signature ~ SM Higgs SM cross section ~3 pb Wbb Wcc Wc non-W Mistags tt Z/Dib Backgrounds! Best channels S/B~1/20 Signal smaller than background uncertainty! 1/2 SM cross section Add tevatron xs plot w/ st normalized to one R. Erbacher - LP07

multivariate techniques can coax signal out from large backgrounds neural network Boosted decision tree multivariate techniques can coax signal out from large backgrounds boosted decision trees, matrix element reconstruction, bayesian neural networks, likelihood discriminants R. Erbacher - LP07

D0 Single top results D0 Results: Search for Single Top 3.4! DØ Combination: 3.6 Boosted decision trees 3.4! Expected significance: 2.3 Taken from users meeting talk-- clean it up a bit. Expected sensitivity: 2.1 First direct measurement of Vtb: 0.68 <|Vtb|< 1 @ 95%CL or |Vtb| = 1.3 ± 0.2 s+t= 4.9 ±1.4 pb s= 1.0, t =4.0 pb PRL 98 18102 (2007) R. Erbacher - LP07

Results for Single Top from CDF New CDF Results: Search for Single Top Observed p-value = 0.09% / 3.1 Expected p-value = 0.13% / 3.0 3.1  Evidence Came much earlier than predicted due to experimental creativity and hard work. LF: Observed p-value = 0.31% / 2.7 Expected p-value = 0.20% / 2.9 Upper limit: 5.14 pb at 95% CL (Bayesian calculation). Median expected limit in background-only pseudoexperiments:
2.06 pb Matrix element: Observed p-value = 0.09% / 3.1 Expected p-value = 0.13% / 3.0 s+t= 2.7 ± 1.2 pb s= 1.1, t =1.3 pb s+t= 3.0 ± 1.2 pb s= 1.1, t =1.9 pb Expected sensitivity: 2.9 Observed significance: 2.7 Expected sensitivity: 3.0 R. Erbacher - LP07

|Vtb|= 1.02 ± 0.18 (expt) ± 0.07 (theory) Using the Matrix Element cross section measurement, CDF determines |Vtb| assuming |Vtb| >> |Vts|, |Vtd| CDF Run II Preliminary L=1.5 fb-1 t-channel s-channel |Vtb|= 1.02 ± 0.18 (expt) ± 0.07 (theory) Z. Sullivan, Phys.Rev. D70 (2004) 114012 D0 |Vtb|>0.68, |Vtb| = 1.3 ±0.2 R. Erbacher - LP07

Forward-Backward Production Asymmetry Forward-Backward Production Asymmetry Afb Forward-Backward Production Asymmetry No asymmetry expected at LO 4-6% expected at NLO in parton frame J. Kuhn, et al. No asymmetry for gg initial states. Qq states with the same final state interfere due to different C eigenstates Reduced asymmetry for tt+jets. Can only see this at the Tevatron? Diagram interferences for qq Smaller asymmetry in lab frame R. Erbacher - LP07 Reduced Asymmetry in tt+jet -- Uwer, et al.

(Uncorrected for reconstruction) First Afb Result from D0 Afb < 0 > 0 How would new physics look? F: fraction of top pair events produced via Z' resonance Replace a Z’ for the gluon in the diagram For MZ' = 750 GeV: F < 0.44 (expected) F < 0.81 (observed) Afb= 12 ± 8(stat) ± 1(syst) % (Uncorrected for reconstruction) R. Erbacher - LP07

Afb CDF First Afb Results from CDF Afb=(28 ± 13(stat) ± 5(syst) ) % NLO: (4-7%) in y*Ql Compare with D0 result: Afb(bkg sub)=(14.4 ± 6.7(stat) ) % Numbers of events measured in two bins: positive and negative values of y.Ql The asymmetry value is background subtracted and corrected for smearing effects of ttbar pair reconstruction with the inversion of 2x2 matrix Afb=(28 ± 13(stat) ± 5(syst) ) % (Fully corrected) R. Erbacher - LP07

Resonances decaying to ttbar New Resonance Production? New D0 Result! See Talk by K. Tollefson Today: Tevatron Striking Results Bump-hunting for Xttbar! R. Erbacher - LP07

(Limits on BR v. stop mass) Can SUSY stop hide alongside top? Stop Search Single-variable separation poor; Construct multivariate discriminant. No evidence for stop (Limits on BR v. stop mass) R. Erbacher - LP07

Top Properties Top Mass Top Quark Width Charge of Top Quark R. Erbacher - LP07

Top Quark Mass: Important EWK Parameter Key role in BSM physics models Constrains the Higgs mass Heavy: Unexpected role in EWSB? Challenges: combinatorics, b-tagging efficiencies, jet energy scale. Solutions: sophisticated analyses, in-situ Wjj calibration What a theorist sees… R. Erbacher - LP07 What an experimentalist sees

Top mass: Exciting Program of measurements at the Tevatron New for summer 2007! New for summer 2007! (not included in March combination) Most precise! R. Erbacher - LP07

Top mass dilepton Many new top dilepton mass results! Combining channels helps: D0 matrix weighting + D0 neutrino weighting  ~4% better for same luminosity Matrix Element Weighting Neutrino-weighting Lepton Pt R. Erbacher - LP07

New Ideas New Ideas! Top mass with cross section constraint: trades stat uncertainty for theory LEPTON+JETS DILEPTON dilepton Top mass extracted from cross sections: Compare to theory and across channels! Consistent with kinematic measurement? Cross section constraint gains you precision in stat at the expense of theory. You gain only until stat~sys NLO QCD calcs including higher order resummations. (Put the mass dependence in here?) Cacciari, Mangano, et al hep-ph/0303085 R. Erbacher - LP07

Top mass Best per channel Mtop=171.6 ± 2.0 GeV/c2 Snapshot: most precise per channel Top mass Best per channel Most precise! all-hadronic from winter 2007: Mt=170.4 ± 3.7(stat+JES) ± 2.1(sys)GeV/c2 Mt=170.4 ± 3.1(stat) ± 3.0(sys)GeV/c2 R. Erbacher - LP07

Top mass summary and combination World Average March 2007: Top mass summary and combination Mtop=170.9 ± 1.9 GeV/c2 See P. Petroff’s Talk (next) for electroweak implications Note that no new averages will be made until CDF/D0 systematics effort is finished with some studies D0-CDF Joint Systematics Effort Underway! New combinations will follow… R. Erbacher - LP07

Top Top quark width Quark Width t < 12.7 @ 95% CL Mt = 175 GeV < 7.5 @ Mtop=170 Blessed July 26th! First direct measurement of top width in run 2! (Lifetime limit with 300 pb-1 from CDF set indirect measurement) R. Erbacher - LP07

Exclude top charge exotic Top Quark Charge: +2/3? Top Quark Charge: -2/3? f+ = 0.87 P-value = 0.31 Are we observing Standard Model top? Standard Model top has charge +2/3 Alternative hypothesis: exotic quark with charge -4/3* Difficult to measure (“t”W+b or W-b) W charge measured through the lepton (straightforward) Bottom charge inferred from jet (difficult) Correctly pair the lepton and b jet (difficult) Select and fully reconstruct top events in lepton+jets (2 b-tagged jets) and dilepton channel (≥1 tagged jet) Determine: flavor of b-jet charge of W (lepton) pairing between W and b (2 fit and Mlb) D0 result with 300 pb-1: See no evidence for exotic model so far… Exclude top charge exotic model XM of -4/3* with 87% C.L. *Chang,Chang,Ma ‘99 R. Erbacher - LP07

Toplight charged higgs Top Event Decays W helicity (V-A) Toplight charged higgs Branching Ratios Top sample (W+c) FCNC R. Erbacher - LP07

t-W-b Coupling t-W-b Coupling V-A? The V-A character of the decay makes the helicity of the W only F0 = 0.70, F- = 0.30, F+ = 0 (longitudinal, left-handed, right-handed) cos* = angle between lepton and top in W rest frame R. Erbacher - LP07

t-W-b Coupling: W Helicity 1-d fit: Fix F0=0.7, fit for F+ D0(1 fb-1) : f+=0.02 ± 0.05 ± 0.05 f+<0.14 @ 95%CL CDF1(1.7 fb-1) : f+=0.01 ± 0.05 ± 0.03 f+<0.12 @ 95%CL CDF2(1.7 fb-1) : f+=-0.04 ± 0.04 ± 0.03 f+<0.07 @ 95%CL 2-d fit: Fit for F0, F+ together CDF1(1.7 fb-1) : f0=0.38 ± 0.22 ± 0.07 f+=0.15 ± 0.10 ± 0.04 CDF2(1.7 fb-1) : f0=0.61 ± 0.20 ± 0.03 f+=-0.02 ± 0.08 ± 0.03 1.7 fb-1 V-A: F0=0.7, F-=0.3 V+A: F0=0.7, F+=0.3 R. Erbacher - LP07

Simultaneous measurement of  and Branching Ratio New measurement by D0! See Talk by K. Tollefson Today: Tevatron Striking Results one analysis is performing the simultaneous xs and R measurement. From that we extract V_tb. Let me call this R=R_b since it's the top decay Br into a b-quark over the top decay Br into all quarks. It is thus a measurement which is sensitive on b disappearance. +0.87 tt = 8.10-0.82 (stat+syst) ± 0.49 (lumi) pb +0.094 R= 0.991-0.085 (stat+syst) R. Erbacher - LP07

Limits on charged higgs Ratio of Cross Sections: Limit on Charged Higgs! Limits on charged higgs R=(pptt)l+jets/(pptt)ll R=1.21 ± 0.26 (stat+sys) Assume tH+b, H+cs only. If MH=MW (not ruled out by LEP): If you get questions about our assumptions on the charged Higgs model:a charged Higgs at 80 GeV which decays predominantly hadronically could be realised in the following scenarios:- general multi-Higgs-doublet model (MHDM). It was demonstrated that such a leptophobic charged Higgs boson with a mass of 80 GeV could lead to noticable effects at the Tevatron if tanbeta < 3.5.- within MSSM: large radiative corrections from SUSY-breaking effects can lead to a suppression of Hｱ -> tau nu compared to Hｱ -> cs. Ah maybe interesting as well: LEP was not sensitive to a 80 GeV charged Higgs because it was in the W mass peak. B(tH+b)<0.35 @95% CL Expected: B(tH+b)<0.25 @95% CL Previous CDF result with 200 pb-1 explores other parameter spaces. R. Erbacher - LP07

First: W+c Cross Section Algorithm Use soft lepton tagger (h.f. jets) Wc: TL, SLT charges are fully anti-correlated, large charge asymmetry A Backgrounds: W+l.f., nonW QCD, DY, etc mostly charge symmetric except DY Observable: same sign subtracted events N(OS) – N(SS) g+s : ~ 90%, g+d: 10% No direct measurement before, reduce systematic uncertainties on many other measurements, probe s-quark PDF and determine Vsc R. Erbacher - LP07

Search for tZc: FCNC Search for tZc: FCNC Tree level FCNC No FCNCs in SM at tree level Allowed in higher order penguins Light quark penguins observed e.g. b→sγ observed by CLEO in 1995, BR O(10-4) Not yet observed for top SM BR: O(10-12) New Physics models predict BRs up to O(10-2) SUSY, Higgs doublet, Warped extra dimensions (J. A. Aguilar-Saavedra, Acta Phys. Polon. B35 (2004) 2695) CDF: First Run 2 limits, better than LEP! See Talk by K. Tollefson Today: Tevatron Striking Results Penguin R. Erbacher - LP07

Summary Summary The top quark is the least known quark, and the most interesting for new physics. The top physics program is very active at the Tevatron, with both precision measurements and first results appearing all the time. Beginning to have sensitivity to the unexpected in particle properties and in the data samples! R. Erbacher - LP07

Conclusions Conclusions R. Erbacher - LP07

Backups R. Erbacher - LP07

D0 single top expected and observed R. Erbacher - LP07

How to extract top width R. Erbacher - LP07

Afb and higher orders R. Erbacher - LP07

CDF Single Top: What Changed ? Likelihood improved treatment of kinematic ambiguities Bug fix in matrix element More MC statistic allows refined training Overall expected sensitivity gain: (as measured on 955 pb-1 analysis) :35% Matrix Element Separate treatment of single and double tag events More refined transfer functions Overall expected sensitivity gain: (as measured on 955 pb-1 analysis) :~10% Common Improvements new ALPGEN Monte Carlo W + Heavy Flavor normalization from W + 1 jet eve nts Define event selection on hadron level jets: CDF Top group wide change More meaningful to theorists Better understood (MET resolution, nonW model..) Causes event migrations: LF loses 1 gains 7 ME loses 5 gains 4 for highest discriminant region R. Erbacher - LP07

Event Yield of DPF and LP Analyses R. Erbacher - LP07

W + Heavy Flavor Estimate Method inherited from CDF Run I (G. Unal et. al.) Measure fraction of W+jets events with heavy flavor (b,c) in Monte Carlo Normalize fractions to W+jets events found in data New improvement: get normalization from W + 1 jet bin (instead of generic dijet sample) Note: Similar for W+charm background Correct data for non W+jets events Heavy flavor fractions and b-tagging efficiencies from LO ALPGEN Monte Carlo Calibrate ALPGEN heavy flavor Fractions from W + 1 jet bin Large uncertainties from Monte Carlo estimate and heavy flavor calibration (~25-30%) CDF Run II Reference for standard method: PhysRevD.71,052003 R. Erbacher - LP07

Heavy Flavor Normalization Improve heavy flavor estimate by calibrating it in W+1 jet side band Take advantage of NN based flavor separator Compare Loose Secondary Vertex mass and NN flavor separator output: consistent results within errors K-factor for heavy flavor: 1.4 ± 0.4 Applied to predict W + Heavy Flavor content of W + 2 jets bin mistags / charm ………. beauty R. Erbacher - LP07

Q*h and Mlnb cross-checks EPD > 0.9 EPD > 0.9 EPD > 0.966 EPD > 0.966 R. Erbacher - LP07

Sensitivity to New Physics and WH Single top rate can be altered due to the presence of New Physics: t-channel signature: Flavor changing neutral currents (t-Z/γ/g-c couplings) - s-channel signature: Heavy W boson, charged Higgs H+, Kaluza Klein excited WKK Z c t W,H+ s (pb) 1.25 t (pb) s-channel single top has the same final state as WHlbb => benchmark for WH search! Tait, Yuan PRD63, 014018(2001) R. Erbacher - LP07

Single Top Candidate Event t-channel single top production has a kinematic peculiarity: Distinct asymmetry in Q x  distribution: lepton charge (Q) x pseudo-rapidity =-log (tan/2) of untagged jet EPD > 0.9 Jet1 Jet2 Lepton Run: 211883, Event: 1911511 Central Electron Candidate Charge: -1, Eta=-0.72 MET=41.6 GeV Jet1: Et=46.7 GeV Eta=-0.6 b-tag=1 Jet2: Et=16.6 GeV Eta=-2.9 b-tag=0 QxEta = 2.9 (t-channel signature) EPD=0.95 R. Erbacher - LP07

The Likelihood 2D Fit Best-Fit Point: Each nuisance parameter fit for at each test value of the cross section. R. Erbacher - LP07

Cos(theta*) kinematics R. Erbacher - LP07