1 / 22

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 +.

chakaluka-davis
Download Presentation

TOP QUARK STUDIES FROM CMS AT LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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… 

More Related