1. Top quark production and properties at D0 E. Shabalina for the D0 collaboration RAS conference November 26-30, 2007

2. Top quark Special place in FNAL physics program Special place in FNAL physics program The only place where top quarks are produced The only place where top quarks are produced 12 years since the discovery 12 years since the discovery The heaviest fundamental particle The heaviest fundamental particle m t = 170.9±1.8 GeV (~1% precision)m t = 170.9±1.8 GeV (~1% precision) Close to a gold atomClose to a gold atom Mass close to scale of electroweak symmetry breaking Mass close to scale of electroweak symmetry breaking May shed light on EWSB mechanism Decays as a free quark Decays as a free quark  = 5×10 -25 s << QCD -1 Passes spin information to its decay products Allows to test V-A structure of SM

3. Top quark properties Produced mostly in tt pairs at the Tevatron Produced mostly in tt pairs at the Tevatron 85% qq, 15% gg85% qq, 15% gg  = 6.8 ± 0.6 pb at NLO  = 6.8 ± 0.6 pb at NLO Dataset: ~1 fb -1, ~10 times more than Run I Dataset: ~1 fb -1, ~10 times more than Run I Precise measurements of top quark properties are possible Precise measurements of top quark properties are possible Most of the current knowledge comes from the studies of top quark pairs Most of the current knowledge comes from the studies of top quark pairs Production of single top quarks: next talk by E. Boos Production of single top quarks: next talk by E. Boos p p t b WW q q’ t b W+W+ ll X Productioncross-section Resonantproduction Production kinematics Top charge asymmetry Top Mass W helicity |V tb | Branching Ratios Rare/non SM Decays Anomalous Couplings CP violation Top Spin Top Charge Top Width _ _ _ _ Production mechanism

4. 4 Top decay channels SM decay: SM decay: E. Shabalina RAS conference 11/26/07 Top pair final states are classified based on W decays Dilepton (ee, μμ, eμ) Dilepton (ee, μμ, eμ) Both W’s decay leptonicallyBoth W’s decay leptonically Lepton (e or μ) + jets Lepton (e or μ) + jets One W decays leptonically, one hadronicallyOne W decays leptonically, one hadronically All-hadronic All-hadronic Both W’s decay hadronicallyBoth W’s decay hadronically τ had +X τ had +X

5. B-jet identification Top, Higgs signal contain b- jets Top, Higgs signal contain b- jets Most of backgrounds do not Most of backgrounds do not B-hadron lifetine ~ 1 ps B-hadron lifetine ~ 1 ps B-hadron travels L xy ~1 mm before decay B-hadron travels L xy ~1 mm before decay Combine properties of reconstructed secondary vertexes and displaced tracks in 7-variable network Combine properties of reconstructed secondary vertexes and displaced tracks in 7-variable network Working point: efficiency ~54%, fake rate ~1% tt event tagging probability ~70% tt event tagging probability ~70% 11/26/07 E. Shabalina RAS conference 5

6. Dilepton channel 11/26/07 E. Shabalina RAS conference 6 57 candidates with nj>=2, 43.9 expected signal,13.3 background use events with 1 jet in emu channel to increase acceptanceeeµµ eµ nj>=2 eµ nj>=1 Z/* 2.42.73.65.5 diboson0.40.51.43.4 fake0.20.41.81.2 Total bckg 3.03.66.710.2 ttbar9.55.828.67.1 Observed1693216 22.5%For m top = 175 GeV  = 6.8 (stat) (syst) ± 0.4(lum) pb ee,eµ,µµ :  = 6.8 (stat) (syst) ± 0.4(lum) pb +1.2  1.1 +0.9  0.8

7. 7 Dilepton combination E. Shabalina RAS conference 11/26/07 Lepton+track channel Looser selection – apply b-tagging Looser selection – apply b-tagging Orthogonal to dilepton Orthogonal to dilepton Use events with nj=1 and nj>=2 Use events with nj=1 and nj>=2 16 candidates with nj>=2 18 expected signal 3.2 background Combined (L=1 fb -1 ) @ m top = 175 GeV CDF best (L=1 fb -1 ) in lepton+track (no dilepton veto): 19%  = 6.2 ± 0.9 (stat) (syst) ± 0.4(lum) pb dilepton :  = 6.2 ± 0.9 (stat) (syst) ± 0.4(lum) pb +0.8  0.7 19.5%

8. 8 Hadronic  +lepton channel Important channel to expand top program (searches for non-SM top decays, H + ) Cross section: use all available top events, assume SM branching Cross section×Br for ttµ(e)+ h (other top contributions are considered to be background) µ+ e+ Selected 29 18 Expected 5.6 4.7 µ+ e+ Selected 29 18 Expected 5.6 4.7 ×Br = 0.126 SM: ×Br = 0.126 CDF (350 pb -1 ) 5 events selected 2.7±0.4 bckg E. Shabalina RAS conference 11/26/07  = 8.3 ± (stat) (syst) ± 0.5(lum) pb +1.4  1.2 +2.0  1.8 Br = 0.19 ± 0.08 (stat) ± 0.07(syst) ± 0.01(lum) pb Pretag After tagging

9. 9 Lepton+jets channel (topology) Update is expected soon, will include events with nj=3 Cross section (L=0.9 fb -1, m top = 175 GeV) Uncertainty 18.5% E. Shabalina RAS conference 11/26/07

10. 10 Top branching fractions =1 in SM  Assumed value of R changes the fraction of events with 0,1 and 2 tags  Perform simultaneous fit of R and ttbar cross section E. Shabalina RAS conference 11/26/07 0 tags, >=4 jets =3 jets>=4 jets 179 single, 58 double tags 76 double tags

11. Results 11/26/07 E. Shabalina RAS conference 11 R=1: 12% Using unitarity of CKM matrix Simultaneous fit result in good agreement with SM: CDF best (L=1.1 fb -1 ): 13%

12. Cross section summary 09/28/07 E. Shabalina (UIC) D0 collaboration meeting 12 The most precise single measurement in the world

13. 13 Cross sections ratio Extract as much physics as possible from the existing measurements Extract as much physics as possible from the existing measurements Ratio is sensitive to the non-W decays of top beyond SM tXb Simplified model: charged Higgs tH ± b with a mass close to W and exclusive H ±  cs (leptophobic higgs in MHDM: hep- ph/9509203, hep-ph/9401311, radiative corrections in MSSM: hep/ph/9907422) FC limit: B(t → H + b) < 0.35 @95% C.L. E. Shabalina RAS conference 11/26/07

14. 14 Top resonances No resonant production is predicted in SM No resonant production is predicted in SM Some models predict ttbar bound states: topcolor assisted technicolor predicts leptophobic Z’ with strong coupling to 3 rd generation Some models predict ttbar bound states: topcolor assisted technicolor predicts leptophobic Z’ with strong coupling to 3 rd generation Narrow width: width is dominated by detector effects Narrow width: width is dominated by detector effects Use lepton+jets events with >=1 b-tag Use lepton+jets events with >=1 b-tag Excluded mass range: M Z’ < 680 GeV @ 95% CL Expected M Z’ < 740 GeV CDF M Z’ < 725 GeV CDF M Z’ < 725 GeV No evidence for a narrow resonance Set upper limit on the  X ×B(Xtt)  tt =6.8 pb Z’ with mass 750 GeV E. Shabalina RAS conference 11/26/07 Search for bumps in ttbar reconstructed mass spectrum Z’

15. 15 Top charge asymmetry No asymmetry in QCD LO, 510% at NLO, even larger at NNLO No asymmetry in QCD LO, 510% at NLO, even larger at NNLO Depends on the region of phase space, any extra jet production Depends on the region of phase space, any extra jet production Reconstruct ttbar pair using kinematic fitter Reconstruct ttbar pair using kinematic fitter Extracted simultaneously with sample composition from the likelihood fit Extracted simultaneously with sample composition from the likelihood fit Do not correct for acceptance and reconstruction effects Do not correct for acceptance and reconstruction effects A = (12 ±8 (stat) ± 1 (syst))% Large positive asymmetry is predicted for Z’ production Leptophobic Z’ Not restricted to narrow Z’ Limits the fraction F of top pairs produced via Z’: E. Shabalina RAS conference 11/26/07 F<0.44 (exp), F<0.81(obs) for Mz’ = 750 GeV

16. 16 W helicity f + = 0.017±0.048 (stat)±0.047 (syst) f + < 0.14 @95% C.L. for f 0 =0.7 (fixed to SM value) Helicity = the relative direction between the spin and the particle's motion SM V-A vertex dictates the fractions extract from cos(*) distribution combine dilepton (two measurements per event and l+jets channels) E. Shabalina RAS conference 11/26/07 dilepton l+jets Model-independent measurement: simultaneously fit f 0 and f + simultaneously fit f 0 and f + measure angle between top quark and down-type fermion (lepton or d,s-quark) allows to use hadronic W-boson decays Coming soon

17. Top quark mass measurement Many techniques TemplateTemplate Matrix ElementMatrix Element Ideogram (hybrid of the above)Ideogram (hybrid of the above) Follow the same pattern: Measure the observable sensitive to the top quark mass Measure the observable sensitive to the top quark mass Map the partons to reconstructed objects (combinatorics!) Map the partons to reconstructed objects (combinatorics!) Calibrate with pseudo- experiments Calibrate with pseudo- experiments Extract the mass from the maximum likelihood Extract the mass from the maximum likelihood 11/26/07 E. Shabalina RAS conference 17 Require a clean mapping between reconstructed objects and partons Jet energy scale calibration is crucial W boson decay products allow to use the known W mass as an in-situ calibration tool

18. 18 Dilepton mass Neutrino weighting Scan potential top quark masses and rapidities Solve for the 4-vectors Assign weights based on comparison of calculated and reconstructed MET Form weight templates for each mass Fit signal and background templates to data Matrix weighting Scan potential top quark masses Solve for top quark momentum assume two leading jets are b-jets 4 solutions per ttbar Include detector resolution Calculate weight as a function of mass for each event E. Shabalina RAS conference 11/26/07 Underconstrained kinematics given two neutrinos 172.5±5.8(stat)±3.5(syst) GeV Dominant Systematics Dominant Systematics ±2 JES ±2.5 GeV ±2 b JES ±2.0 GeV ±0.9 GeV Template statistics ±0.9 GeV 4% 175.2±6.1(stat)±3.4(syst) GeV CDF: 2.5% @1.8fb -1 ME

19. 19 Matrix Element method Pioneered by D0 and provides the most accurate measurement of the top quark mass Calculate per-event probability density for signal and background as a function of the top quark mass using 4- vectors of reconstructed objects Multiply the event probabilities to extract the most likely mass Maximizes statistical power by using all event information Extremely CPU intensive (most recent result required >0.5 M grid-hours for integration) E. Shabalina RAS conference 11/26/07

20. 20 Lepton+jets mass (ME) LO matrix element is used to calculate probability Transfer functions: map measured quantities (x) to parton-level ones The jet energy calibration (JES) is a free parameter in the fit, constrained in-situ by the mass of hadronically decaying W 1.6% (CDF: 1.25% @1.7fb -1 ) E. Shabalina RAS conference 11/26/07 m=170.5± 2.4 (stat+JES) ±1.2 (syst) GeV  Use b-tagging information to reduce combinatorics  Weight each jet-parton assignment with b-tagging event probability 24 possible weighted assignments between jets and partons 0.9 fb -1

21. 21 Mass combination and summary New Tevatron average top mass is planned for Moriond’08 Requires a lot of work on systematics together with CDF E. Shabalina RAS conference 11/26/07 173.7±5.4 (stat)±3.4 (syst) GeV Dilepton combined: 173.7±5.4 (stat)±3.4 (syst) GeV 172.1 ± 1.5 (stat) ± 1.9 (syst) GeV D0 combined: 172.1 ± 1.5 (stat) ± 1.9 (syst) GeV 3.7% 1.4% 1.3% CDF

22. 22 Conclusion Top quark is the least knows quark and the most interesting for new physics Top physics has entered the era of precision measurements, we (finally!) have plenty of top quarks Many top properties measurements are just beginning to have sensitivity There is still a lot to understand about top! E. Shabalina RAS conference 11/26/07

23. Backup slides 11/26/07 E. Shabalina RAS conference 23

24. 24 Search for scalar top Stop is predicted by SUSY Consider m stop <= m top  1 + and  0 masses - close to their experimental lower limits m stop : 145-175 GeV  1 + : 105-135 GeV Same final state as ttl+jets Use kinematic fitter to reconstruct events to ttbar hypothesis Build discriminant to separate top from stop regular kinematic variables fit output Limit is 7-12 times higher than MSSM E. Shabalina RAS conference 11/26/07 stop

25. 25 Single top Since evidence ME and BNN analyses were updated Since evidence ME and BNN analyses were updated All three show similar sensitivity All three show similar sensitivity Results are combined Results are combined (tb+tqb)=4.7 pb p-value 0.014% significance 3.6 E. Shabalina RAS conference 11/26/07

26. 26 Mass from cross section What mass do we measure? Depends on the convention… Pole mass? MS? Pmas(6,1) in Pythia? – probably the closest given the analysis techniques Cross sections are less dependent on the details of signal simulation Extract for dilepton and l+jets channels independently Depends on theory prediction: Cacciari et al Kidonakis, Vogt (lepton+jets, Kidonakis and Vogt) E. Shabalina RAS conference 11/26/07 m=166.9± (stat+sys) (theory) GeV +5.9  5.2 +3.7  3.8