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TOP QUARK STUDIES FROM CMS AT LHC

TOP QUARK STUDIES FROM CMS AT LHC. Marc M. Baarmand Florida Institute of Technology PHYSICS AT LHC Prague, Czech Republic, July 6-12, 2003. b. q’. p. Top Quark Physics. W Helicity. Top Mass. l +. Top Width. Anomalous Couplings. Production cross-section. Top Spin. W +.

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TOP QUARK STUDIES FROM CMS AT LHC

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  1. TOP QUARK STUDIES FROM CMS AT LHC Marc M. Baarmand Florida Institute of Technology PHYSICS AT LHC Prague, Czech Republic, July 6-12, 2003

  2. b q’ p Top Quark Physics W Helicity Top Mass l+ Top Width Anomalous Couplings Production cross-section Top Spin W+ CP Violation Top Charge p n Resonance production t b _ X Production kinematics _ _ t q Rare/non SM Decays W- _ Branching Ratios |Vtb| ; Single top production

  3. Topics in This Talk • Top production properties • Top cross section • Top mass • Top spin effects • Top-antitop spin correlations • Anomalous couplings • FCNC in top physics • Non-Standard-Model decays of top • Search for charged Higgs • Single top production; top partial width, Vtband spin effects…  see talk by Sherstnev • More in proceedings of “SM physics (and more) at the LHC” CERN 2000-004

  4. Standard Model: t  Wb dominates, BR for ttfinal states 21% t + X m + jets 44% e + jets e + e e + m (Drell-Yan) 15% m + m all - hadronic 15% 1% 3% 1% (W-g fusion) Top Quark Production and Decay • Strong tt pair productionEW single top quark production

  5. tt Production Cross Section • Motivation • tt cross section is a test of QCD predictions • Inclusive and differential cross sections • A discrepancy may indicate possible new physics • Production via a high mass intermediate state • Non Wb decay model • Measurements performed using various final states • Dilepton channels • ee, e and  • Lepton + jets channels • e+jets, +jets: topological analysis and b-tagging • All hadronic channel • Topological variables and b-tagging • Neural networks techniques • Trilepton channels

  6. CDF dilepton DØ dilepton DØ topological CDF lepton-tag DØ lepton-tag CDF SVX-tag CDF hadronic DØ hadronic CDF combined DØ combined 4.7 -6.2 pb theory Berger et al. Bonciani et al. Laenen et al. Nason et al. Tevatron tt Cross Section RUN 1 D: PRL 79 1203 (1997); CDF: PRL 80 2773 (1998)(+updates)

  7. tt Production at LHC • tt cross section at LHC (√s = 14 TeV)  830 pb • LHC is a Top factory: 108 tt in 100 fb-1 • Measurement of s with high statistical precision • Measurement of ds/pT up to TeV in pT • Full understanding of top needed for evaluation of backgrounds to Higgs, SUSY, etc. • Challenge is to control systematics • Experiment: a few percent?! • Theory: currently 12% but expect improvements (next slide) • Relation to top mass: • Within SM expect Dmt/mt 0.2 Ds(tt)/s(tt) • If 5% precision in cross section is achieved • Indirect determination of mt withDmt 1.8 GeV!

  8. Theoretical Uncertainties PDF: ±10% scale: ±6%

  9. t H W W W W b Top Quark Mass • Fundamental parameter of Standard Model • Tevatron Run 1: 174.3  5.1 GeV • Affects predictions of SM via radiative corrections Measurements of MW = 80.398±0.041 GeV and mt constrain MH • Large mass of top quark • Yukawa coupling  1 • Clues about electroweak symmetry breaking! Light Higgs !

  10. CMS Top Mass Studies • Lepton + jets • Dmt = 1.0 – 1.5 GeV depending on pT modeling and calibration precision • W-jj, b-jet resolution, combinatorics… • Dilepton • Dmt ≤ 2 GeV obtained from correlation between M(e m) and mt

  11. Promising Channel • l + J/y channel • Dmt ≤ 1 GeV strong correlation between M(l J/y) and mt • Sensitivity to b fragmentation function • Small BR (5x10-5) • Suitable for high luminosity data !

  12. tt Spin Correlations • tt → l+ l’- X (l=e,m) with pure V-A top decays • Expect C = 0.332 for LHC using CTEQ4L L. Sonnenchein CMS PhD thesis

  13. CMS Study Fit  C = -0.021 ± 0.022 C = 0.331 ± 0.023 PYTHIA 6.1 + M.E. by S. Slabospitsky ISR, FSR, multiple int., detector response included, corrected for selection cuts

  14. FCNC in Top Quark Physics • Flavor Changing Neutral Current couplings tVc and tVu; V = g, g, Z • Absent at tree-level and highly suppressed in SM • Present through loop contributions • Observation of top quark FCNC processes • New Physics!

  15. FCNC in Top Decays • tt pair production • Background processes

  16. Branching Ratios • Expected constraints on “BR” = Г(tVq) / Г(SM) • Tevatron Run 2 • LHC – CMS • Linear e+ e- collider . BR’s significantly constrained – allowing test of SUSY scenarios

  17. Non-SM Decays of Top • Supersymmetry • Presently observed bosons and fermions would have more massive superpartners (SUSY is a broken symmetry) • SUSY Higgs sector – two Higgs doublets (MSSM) • 5 states (h0,H0,A0,H+,H-) survive after giving W & Z masses • H LEP limit 77.4 GeV (LEP Working Group 2000) • Decay t  H+ b can compete with t  W+ b • H couples to heaviest fermions  detection through breakdown of e / m / t universality in tt production

  18. DØ Indirect search for t  H+ b; disappearance of SM t  W+ b Direct search for t  H+ b; with H+t n for large tan b PRL 88, 151803 (2002) Tevatron Search - Run 1 CDF Direct search for t  H+ b; with H+t n for large tan b PRD 62, 012004 (2000) H+ W bb H+ t n H+ c s B(t  H+ b) < 0.36 @ 95% CL if B(H+t n)  1 and MH < 160 GeV

  19. Expectation from Tevatron Run 2 Excluded regions expected from Run 2 Large regions of parameter space for MH < mt remain to be searched!

  20. CMS Search • One CMS study searches for excess of t jets in tt events • t jets identified as narrow hadronic jets • dilepton deficit used to enhance the search min L to exclude tWb (2s) min L to discover tHb (5s) Possible to explore MH < 160 GeV and 2<tanb<40 with 30 fb-1

  21. Charged Higgs Boson • 5 s discovery reach for light and heavy Higgs • See talks by A. Nikitenko R. Kinnunen Search in top quark decays

  22. Summary • Top quark physics is rich, exciting and doable at low luminosity LHC • SM: EW and QCD tests • BSM: probe SUSY • Today’s signal, tomorrow’s background • Top quark (pair and single) production is the main background to processes with multi lepton + jets in final state, e.g. SUSY • Although top will be explored at Tevatron, it will have to be re-visited at LHC for high statistics studies • Dmt ≤ 1 GeV • BR for FCNC tVq  10-3 - 10-6 • Lots of work and fun ahead… 

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