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Observables to distinguish BSM Z'->tt vs QCD and W+jets in leptonic top decays at ATLAS

Observables to distinguish BSM Z'->tt vs QCD and W+jets in leptonic top decays at ATLAS. _. Madalina Stanescu-Bellu , DESY Under supervision of: Dr. Klaus M ö nig, DESY DPG Tagung 25 March 2014. Introduction ttbar resonances. E t miss. Muon. ttbar resonances: new particle X → ttbar

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Observables to distinguish BSM Z'->tt vs QCD and W+jets in leptonic top decays at ATLAS

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  1. Observables to distinguish BSM Z'->tt vsQCD and W+jets in leptonic top decays at ATLAS _ Madalina Stanescu-Bellu, DESY Under supervision of: Dr. Klaus Mönig, DESY DPG Tagung 25 March 2014

  2. Introduction ttbar resonances Etmiss Muon • ttbar resonances: • new particle X → ttbar • look for bump in the Mttbar spectrum • leptophobic topcolor Z’ : • a new Z-like boson • couples strongly to top • narrow: Γ/M ~ 3% (ATLAS resolution=7%) • color singlet transverse display of μ+jets ttbar event 10TeV data, Mttbar = 2.5 TeV ATLAS-CONF-2013-052

  3. Introduction ttbar resonances M ttbar • JET: • hadronic+em shower in calorimeters • ELECTRON: • tracks in the inner detector • em clusters => included in jets • MUON: • tracks in the inner detector + muon spectrometer • minimum ionizing particle (no energy left in the calorimeter) • => reconstructed separately from jets • TERMINOLOGY: • R2=dφ2+dη2 • fat jet (FJ): Anti-kT, R=1.0 • narrow jet (NJ): Anti-kT, R=0.4 RESOLVED BOOSTED probability of the top decay products to be within ΔR=0.8 10TeV Simulation ATL-PUB-PHYS-2010-008

  4. Selection of boosted ttbar events • semi-leptonic boosted events: • ttbar → Wb + Wb → lnb + qqb • PROBLEM:lepton might merge with the b – narrow jet • ATLAS default approach:resolved narrow jets and isolated leptons • my NEW approach: b – narrow jet and lepton in one fat jet • advantage: includes FSR , better for Mttbar calculation • fat jets (FJ): • pTFJ>350GeV (entire top decay to be in the FJ)

  5. Selection of boosted ttbar events hadronic top • HADRONIC TOP = HADRONIC FJ: • η<2, M>100GeV • opposite φ hemisphere to the lepton(in φ, because η varies due to PDF) leptonic top

  6. Selection of boosted ttbar events • LEPTONIC TOP: • NEW: • all above objects : same φ hemisphere • hadronic component: pT > 50GeV • no use of b-tagging • lepton close to FJ: ΔRlepton – FJ < 1 e- : already included in FJ μ- : add to FJ • (to be consistent to e- ) • u: reconstructed with M W constraint • η<1.5 (smaller than hadronic FJ case, for lepton space )

  7. Prompt vs decay μ in Z’->ttbar signal events prompt μ W nμ hadronic component t • decay μ: • resemble QCD => useful to understand QCD • could be badly reconstructed as prompt μ • high discrimination power: Mhadronic component • less discrimination power : ΔR μ - hadronic component b q W q t hadronic component PROMPT μ DECAY μ ATLAS simulation work in progress ATLAS simulation work in progress B meson q decay μ ΔR μ – hadronic component M hadronic component M hadronic component

  8. μ discrimination power ATLAS simulation work in progress ATLAS simulation work in progress • discrimination power Z’->ttbar 3TeV prompt μ (signal ) vs: • QCD: all variables • Z’->ttbar 3TeV decay μ : all variables (looks similar to QCD) • W+jets: ΔRμ– hadronic component

  9. e- calibration • search the candidate b-NJ: • NJ highest in pT, close to leptonic FJ • object different than lepton : ΔRlepton – NJ > 0.2 • there SHOULD BE : Eleptonic FJ ≥ Eb-NJ + Elepton

  10. e- calibration ABOVE diagonal leptonic FJ = b-NJ + FSR + lepton ON diagonal e- Eleptonic FJ [GeV] BELOW diagonal ATLAS simulation work in progress Eb-NJ+Elepton [GeV] e- : unexpected values below the diagonal μ- Eleptonic FJ [GeV] ATLAS simulation work in progress ATLAS simulation work in progress Eb-NJ+Elepton [GeV]

  11. e- calibration: pT balance leptonic vs hadronic top ABOVE diagonal BELOW diagonal ATLAS simulation work in progress ATLAS simulation work in progress NOT BALANCED pT leptonic top / pT hadronic top pT leptonic top / pT hadronic top ON diagonal ATLAS simulation work in progress leptonic top = b-NJ + FSR + lepton+ n pT leptonic top / pT hadronic top

  12. e- calibration: pT balance leptonic vs hadronic top replace leptonic top with resolved calculation

  13. RESOLVED e- calibration: pT balance leptonic vs hadronic top ABOVE diagonal BELOW diagonal ATLAS simulation work in progress ATLAS simulation work in progress Now unbalanced, because FSR is missing BALANCE RECOVERED !!! pT leptonic top / pT hadronic top pT leptonic top / pT hadronic top ON diagonal ATLAS simulation work in progress leptonic top = b-NJ + lepton+ n pT leptonic top / pT hadronic top

  14. e- calibration: pT balance leptonic vs hadronic top • cause of pT unbalance: • maybe b-NJ not fully included in leptonic FJ ? • ΔRleptonic FJ – bNJ = [0, 0.3] => b-NJ fully included in leptonic FJ • ΔRe - bNJ = [0.2, 0.5] => e- within [0.2, 0.5] to NJ are miscalibrated to hadronic jet energy scale BELOW diagonal BELOW diagonal ATLAS simulation work in progress ATLAS simulation work in progress ΔRe - bNJ ΔRleptonic FJ – bNJ

  15. Summary • found a few variables with discrimination power Z’ vs QCD and W+jets: • e- within [0.2, 0.5] to narrow jets: • are miscalibrated to hadronic jet energy scale • produce pT unbalance leptonic top - hadronic top

  16. BACKUP

  17. hadronic top p p hadronic component =leptonic FJ– lepton hadronic component lepton n leptonic FJ leptonic top = leptonic FJ + n

  18. hadronic top p p leptonic FJ = b-NJ + FSR + lepton b-NJ FSR lepton n leptonic FJ leptonic top = leptonic FJ + n

  19. hadronic top p p leptonic FJ = b-NJ + FSR + lepton b-NJ FSR lepton n leptonic FJ leptonic top = b-NJ +lepton +n

  20. Discrimination power Z’ (3TeV)vs W+jets vs QCD ATLAS simulation work in progress ATLAS simulation work in progress • Leptonic Top mass: • Separates QCD and Decay μfrom Z’ Prompt leptons • Ttbar mass: • Separates W+jets and QCD from Z’ Prompt leptons • Hadronic component mass of the leptonic top: • Separates Z’ decay μ from Z’ Prompt leptons ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ELECTRONS MUONS

  21. Electron Comparison E,Pt,Pz,M ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress E and Pt of Leptonic FatJet can be used to cut out W+jets

  22. Muon Comparison E,Pt,Pz,M ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress ATLAS simulation work in progress E and Pt of Leptonic FatJet can be used to cut out W+jets

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