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“Optimizing Semi-Leptonic Top Reconstruction at Johns Hopkins University event”

This study explores the semi-leptonic top reconstruction at Johns Hopkins University event, focusing on mini-isolation techniques and leptonic cuts efficiencies for boosted tops. The research emphasizes avoiding MET for discrimination and not b-tagging inside of jets to improve event generation and reconstruction processes. Using PYTHIA event generation software, the study evaluates various isolation cone definitions and mini-isolation methodologies to enhance top reconstruction and discrimination against physics and instrumental backgrounds. Efficiency and cut analyses provide insights into isolating top events from heavy flavor decays and radiative processes, contributing to a comprehensive strategy for experimentalists. This comprehensive approach aims to optimize the identification and reconstruction of semi-leptonic tops while minimizing background interference, leading to more accurate experimental results at the Johns Hopkins University event.

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“Optimizing Semi-Leptonic Top Reconstruction at Johns Hopkins University event”

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  1. Semileptonic Boosted Tops Brock Tweedie Johns Hopkins University 10 July 09 K. Rehermann & B.T., To Appear

  2. The Problem b-jet l ~ mt / pt n Isolation probability (DRbl > 0.4)

  3. Our Philosophy • Try to use these nonisolated leptons • Avoid using MET for discrimination • Do not b-tag

  4. Leptons Inside of Jets • Physics backgrounds • Heavy flavor (prompt and radiative) • p+ decays in flight • Instrumental backgrounds • p0C “e” • p+C “m” Save for real experimentalists!

  5. Event Generation • PYTHIA and HERWIG ttbar continuum and generic dijet • Includes prompt heavy flavor, light meson decays-in-flight in LHC-like detector volume • Basic requirement: muon with Pt > 30 GeV • ~4% pass rate for dijet…per-jet probability ~2% I will exclusively use PYTHIA plots / #s. HERWIG is practically identical.

  6. m+jets Event Reconstruction • Set aside leading muon • Put remaining particles into perfect 0.1x0.1 calorimeter • Cluster with C/A • Set R according to Ht in hemisphere opposite the muon • Jet Pt > 50 GeV • Leading jet == hadronic top • Jet closest to muon == b-jet from semilep top

  7. Semi-Leptonic Tops vs Light Jets b b • m + jet + MET • hard m and MET • mT(m+MET) ~ mW • mass = mt n n b n m b m p m K • m + jet + MET + JUNK • Soft/collinear singularities • Splittings more common late in the shower (more gluons!)

  8. Mini-Isolation DR ~ mt / Ptt DR ~ ? DR ~ mb / Ptb DR ~ mb / Ptb m n m n B B B W t

  9. Mini-Isolation • Many options for cone definition: • R ~ 1/Ptb ~ 1/Ptm • R ~ 1/Ptt • R = fixed # • … • They all perform comparably • R ~ 1/Ptm convolves additional discriminating power from muon Pt distributions

  10. Mini-Isolation Isolation cone DR = (15 GeV) / Ptm top light jet W+jets Demand >90% isolated

  11. (Thaler & Wang) xm = 1 - mb2/mbm2 top light jet W+jets Demand xm > 0.5

  12. Mini-Isolation After xm Cut top light jet W+jets

  13. xm After Mini-Isolation Cut top light jet W+jets

  14. Efficiencies of Leptonic Cuts (Pt ~ 1 TeV)

  15. Efficiencies of Leptonic Cuts (Pt ~ 2 TeV)

  16. Semi-Leptonic Tops vs W-strahlung b q’ • m + jet + MET • hard m and MET • mT(m+MET) ~ mW • mass = mt n n q b n m W m m • m + jet + MET • hard m and MET • mT(m+MET) ~ mW • mW < mass < sqrt(s-hat)

  17. Ideal Top Mass Distributions top light jet W+jets

  18. DRbm • Wjj MadGraph 2 C 4 top light jet W+jets

  19. Ideal-Mass vs DRbm Discrimination

  20. Efficiencies of Leptonic Cuts (Pt ~ 1 TeV)

  21. Efficiencies of Leptonic Cuts (Pt ~ 2 TeV)

  22. Backgrounds with Top-Mass Cut Now use MET for global even reco. Define hn == hm. Hadronic top-mass cut efficiencies: et ~ 85% / eq/g ~ 25%

  23. Backgrounds with Top-Tag

  24. Resonance Efficiencies (incorporates m+jets BR) top-mass cut top-tag

  25. Summary • Assuming this all works in the detector, light QCD can be made negligible practically “for free” • In principle, rejection factors at the ~50,000 level • Allows for a comfortable margin of theory error • W-strahlung is still non-negligible • O(1) rejection “for free” by exploiting geometry

  26. Summary • Still various additional discriminators after incorporating MET • mT(top), m(top) • Internal angular variables • Possibilities for improvements in high-Pt t-tagging and b-tagging

  27. Summary • We will be seeing how these perform in full CMS simulation in the coming months

  28. Extras

  29. Resonances

  30. Discovery Reach Estimates S/sqrt(B) > 5 & S > 15 G = 0% G = 15%

  31. Subjet Rates * old PYTHIA results

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