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Top Quark Physics at TeV Energies

Top Quark Physics at TeV Energies. Quarks – origin and properties Spectroscopy of hadrons Mass and decay of top quark Production mechanism Spin and spin correlations Graviton and other dynamics. p. p.

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Top Quark Physics at TeV Energies

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  1. Top Quark Physics at TeV Energies Quarks – origin and properties Spectroscopy of hadrons Mass and decay of top quark Production mechanism Spin and spin correlations Graviton and other dynamics TopPhysATLAS-FJFI2008

  2. TopPhysATLAS-FJFI2008

  3. p p • What do we expect from a proton-proton collision at a centre-of-mass energy of 14 TeV? • Perturbative QCD is highly successful when applied to hard processes (large-pt) but cannot be applied to soft interactions (low-pt). TopPhysATLAS-FJFI2008

  4. TopPhysATLAS-FJFI2008

  5. TopPhysATLAS-FJFI2008

  6. TopPhysATLAS-FJFI2008

  7. stt(th)=825±150 pb NNLO-NNNLL: Kidonakis, Vogt, PRD 68 (03) 114014 8 millions tt pairs/year (1 pair/second) at low luminosity! qq->tt: 13% gg->tt: 87% Top decays classification: di-lepton, lepton+jets, all jets TopPhysATLAS-FJFI2008

  8. gg->tt: 87% Top decays classification: di-lepton, lepton+jets, all jets charge, mass, spin, decay, dynamics of production Top quark properties: TopPhysATLAS-FJFI2008

  9. 2005: M t= 172.7 ± 2.0 GeV Mh < 186 GeV TopPhysATLAS-FJFI2008

  10. Qt = +2/3 Qt = -4/3 Atlas • t coupling to photon • can be probed via t tbar  events • can also be used to confirm Q=2/3 • SM: • Br(t Wb)  99.9% • Br(t  Ws)  0.1%, • Br(t  Wd)  0.01% • Many Beyond SM models involve anomalous top couplings • Several possible rare decay modes (eg. FCNC) have clear experiment signatures and, if observed at the LHC, would be evidence for new physics pT() [GeV] TopPhysATLAS-FJFI2008

  11. Semileptonic channel: Atlas • 0.2% efficiency • Total background 5% • Mass extracted from jjb system • (-> large error from jet scale uncertainty) • Stat. error: ±0.25 GeV • Error from Pt(t) spectrum: ±0.4 GeV • Jet scale: DEj/Ej~1% -> DM~±0.3 GeV • Require: • Isolated lepton with pT(l)> 20 GeV • Exactly 4 jets (R=0.4), each with pT(j) > 40 GeV • No b-tagging used • Plot m(jjj) of combo with max pT mt  1-2 GeV TopPhysATLAS-FJFI2008

  12. Dilepton channel hep-ex/0403021, EPJCdir0403 TopPhysATLAS-FJFI2008

  13. Unfeasible at low luminosity • Independent from jet scale • Promising at high luminosity • Among main systematics: • b fragmentation mt  1 GeV TopPhysATLAS-FJFI2008

  14. f0 t t t b W Polarization in Top Decays hep-ex/0508061 TopPhysATLAS-FJFI2008

  15. V-A weak interaction determines the top quark decay in SM TopPhysATLAS-FJFI2008

  16. Polarization of Top TopPhysATLAS-FJFI2008

  17. « Spin studies in tt pairs » TopPhysATLAS-FJFI2008

  18. κ= 0 κ= -0.34 SM LO TopPhysATLAS-FJFI2008

  19. TopPhysATLAS-FJFI2008

  20. Atlas κ= 0 κ= -0.34 SM LO TopPhysATLAS-FJFI2008

  21. Neutral Higgs boson φ with unspecified CP parity W. Bernreuther, M. Flesch, P. Haberl – Phys. Rev. D58 (1998) a, ã – reduced scalar and pseudoscalar couplings (SM Higgs boson: a=1, ã=0) TopPhysATLAS-FJFI2008

  22. top quark Yukawa coupling can be measured from t tbar H production for m(H) < 130 GeV, Hbb is dominant decay • ttH final state is WWbbbb) • look for events with one W l, • the other W jj • pT(lep) > 20 GeV • Njet  6 with pT(jet) > 15 GeV • Nbjet = 4 TopPhysATLAS-FJFI2008

  23. Single Top Production 3,000,000 events/yr TopPhysATLAS-FJFI2008

  24. Atlas • there are large bkgnds (eg. tt [830 pb], Wbb [>300 pb]) with similar final states • ability to extract signal depends critically on detector performance, including • look at lepton, jet, bjet multiplicities, as well as kinematic distributions, to separate single top processes from ttbar, Wjj, Wbb, as well as from each other Jet eta TopPhysATLAS-FJFI2008

  25. Each process is sensitive to possible new physics in different ways • Some examples: • heavy W’  enhancement in s-channel W* • FCNC gu  t  enhancement in “Wg fusion” • It is important to measure each process separately • Also want to measure W, top helicities • Eg. sensitivity to V+A, anomalous couplings TopPhysATLAS-FJFI2008

  26. Graviton ? Only for Gravitation would be visible TopPhysATLAS-FJFI2008

  27. While supersymmetry is required for supergravity, it was normally assumed that any unification of forces would occur at the Planck scale ~1019 GeV very large hierarchy between the electroweak scale and gravitational scales New idea:Gravity may propagate in extra dimensions, while the gauge particles and fermions remain trapped in 3+1 dimensional spacetime extra dimensions n not necessarily small in size (millimeters) true Planck scale may be as low as the electroweak scale Gravity could start to play a role in experiments at ~ TeV LHC [hep-ph/9905257] TopPhysATLAS-FJFI2008

  28. Virtual graviton and top production [hep-ph/9811501, hep-ph/0010010] Errors on SM LHC For 0.3 0.5 1.0 pb Variation of cross section with variation of Ms scale at Tevatron and LHC For LHC the dashed lines correspond to errors on the SM cross section of 0.3, 0,5 pb At LHC it is expected that the Ms value 2.5-5 TeV can be probed in this channel Two models TopPhysATLAS-FJFI2008

  29. For pp collider Sensitivity large in forward/backward regions e.g. TopPhysATLAS-FJFI2008

  30. Phys.Rev. D70, p15015, 2004e-Print Archive: hep-ph/0409273 Helicity angle correlations in model with graviton (MD = 0.5 TeV, λ = 1) A = +0.97 The influence of extra-dimensions on the spin correlations of top-antitop quarks could be visible at the LHC in the case the effective scale MD is lower than ~1.5-2 TeV TopPhysATLAS-FJFI2008

  31. TopPhysATLAS-FJFI2008

  32. 1 TeV t t t b b b  c 1 GeV c c s s s  d d d  1 MeV u u u  e 1 keV e 1 eV • One of the most urgent problems in HEP to identify the mechanism of EWSB and mass generation, • in which the top quark may play a special role. • The LHC has a large potential for discovery of New Physics effects: e.g. heavy tt resonances, FCNC decays, etc… • Test some models beyond SM : • New type of interactions (resonant Higgs, extra-dimensions, …) • Modifications of SM couplings : • anomalous gtt couplings • anomalous Wtb coupling Top quark physics with special properties (high mass, fast decay,..) may open new Physics beyond Standard Model u d s c b t TopPhysATLAS-FJFI2008

  33. TopPhysATLAS-FJFI2008

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