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Z -> t t

Signal and branching fractions Backgrounds and Triggers for the different “signatures”. Z -> t t. Z -> t t ->. t t -> t h t h n n s* b = 82 pb t t -> t h e n n n 39 pb t t -> t h m n n n 39 pb t t -> m e n n n n 12 pb

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Z -> t t

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  1. Signal and branching fractions Backgrounds and Triggers for the different “signatures” Z -> t t

  2. Z -> t t -> ... • t t -> th th n n s*b = 82 pb • t t -> th e n n n 39 pb • t t -> th m n n n 39 pb • t t -> m e n n n n 12 pb • t t -> m m n n n n 6.2 pb • t t -> e e n n n n 6.2 pb

  3. Z -> t t -> ee/mm • Background: • Z-> ee , Z-> mm : s*b 30 times higher than for signal • as n in t decays aligned with t no difference in Df • leptons have lower pt for signal (bad…) • invariant mass - mZ • But be aware: g* contribution…

  4. pT electrons > 10 GeV (DIEL trigger) Z -> t t : .5% (.125) 20% of signal Z -> ee : 38% QCD: 0.02%: 1 event (from4528 events with pt>20 GeV) ee inv. mass < 60 GeV: 1% Z -> ee left reinvestigate single e with higher statistic Z -> t t -> ee

  5. pT muons > 4 GeV (DIMUON trigger) Z -> t t : 1.1% (.3% background), 36% Z -> mm: 36% QCD: 9% of events with pt>20 GeV inv. mm mass < 60 GeV: 9% Z -> mm left 0.6% from 800 W mn+fake Z -> t t -> mm

  6. Z -> t t -> e m • s = 12 pb • Physics background: WW-> e m n n (0.2 pb) top top-> b b e m n n • QCD via misidentification (Zee, Zmm,W…) • MU_EM: L1 e > 5 GeV, L2> 10 GeV L1,L2 m > 4 GeV

  7. em: 16% eff 28 events (22 in right category) with projecting the MET back-> Z mass statistics too low for a meaningful plot Z -> t t -> ee/mm/em

  8. Z -> t t -> th lep • Signal s = 39 pb each • Backgrounds: • QCD misidentification • Z(+ jets)-> ll + jets with misid+inefficiency • W(+jets) -> l + misid • WW -> e th n n • th: for now require NN>0.4

  9. Z -> t t -> th lep • Possible triggers (electron case):A) Single electron: e pt>15GeV B) electron+jet: e pt> 10 GeV, jet> 10GeV C) electron+t: e pt>5 GeV (needs track trigger) • Muon case: A) Single m : threshold 7 GeV B) m + jet: m pt > 4 GeV but jet ET>20 GeV C) m + t : m pt > 4 GeV and 5 GeV t

  10. Z -> t t -> th lep

  11. Z -> t t -> th th • Di tau trigger: needs track trigger • requires two tracks > 5 GeV, one with preshower + 2 jets > 3 GeV • difficult to study without trigger simulator...

  12. QCD blue: m red: e black: em Z -> t t -> th lep

  13. Z -> t t - needed: • Working trigger simulator with events that can be processed by it • root-tuples (or at least reco files) of: • Signal Z -> t t about 10k events • QCD files • W->e n, W-> m n, Z->other, same statistics • other backgrounds as top, b, WW

  14. Z -> t t - Conclusions • Only leptonic decays: • expect about 20% efficiency • probably only em mode usable • Leptonic hadronic mode: • efficiencies about 25% (40% without t req) • Only had: need trigger simulator • And overall: need more statistics …

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