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tth, (h → bb): Cuts-Based analysis status/progress

tth, (h → bb): Cuts-Based analysis status/progress. Chris Collins-Tooth 06-Feb-2007. Samples. Using Common Analysis, v00-01-05 (see TWiki) https://uimon.cern.ch/twiki/bin/view/Atlas/TthhbbAnalysis - ttH_rootples_Example_Analysis Signal tth(h → bb): 5340 (forced l + )

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tth, (h → bb): Cuts-Based analysis status/progress

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  1. tth, (h→bb): Cuts-Based analysis status/progress Chris Collins-Tooth 06-Feb-2007

  2. Samples • Using Common Analysis, v00-01-05 (see TWiki) • https://uimon.cern.ch/twiki/bin/view/Atlas/TthhbbAnalysis - ttH_rootples_Example_Analysis • Signal tth(h→bb): • 5340 (forced l + ) • 5341 (forced l - ) • Backgrounds used: • 5855 AcerMC gg->ttbb (QCD) • 5214 AcerMC gg->ttbb (EW) • 5212 MC@NLO/Herwig ttjj (jj=bb removed).

  3. Cuts Used (see v00-01-05) • Lepton: • e: Pt>25 GeV; EtCone<15 GeV;isEM 0x4FF; auth=1||3. • .mStaco: Pt>20 GeV; 2/dof<50 < ; EtCone40<50 GeV. • Jets: 6j; Pt>20 GeV; ||<5. • bJets: 4bj; bjetWeight 5. • Neutrino Solution: use colinear appx if no solution. • Sample 5212 (ttjj) only: remove if 4 unique bquarks • MWlep/had: 80.4  25 GeV. • Mt: 175  20 GeV. • Background + Combinatorics: Pt(J12+J22)>75 GeV (see later)......

  4. Signal and BG Efficiencies. • Latest “full sim” is Compared to Cammin [ATL-PHYS-2003-024] • Applied same cuts as Cammin and saved v00-01-05 • On the whole encouraging. • Problem with ttjj • many events had >=4 unique b-quarks • Had to remove them, as ttjj(jj=bb)  ttbb

  5. Signal and BG Efficiencies. higher jet mult. in MC@NLO? • Latest “full sim” is Compared to Cammin [ATL-PHYS-2003-024] • Applied same cuts as Cammin and saved v00-01-05 • On the whole encouraging. • Problem with ttjj • many events had >=4 unique b-quarks • Had to remove them, as ttjj(jj=bb)  ttbb

  6. Signal and BG Efficiencies. higher jet mult. in MC@NLO? cut on 2 tops too harsh? • Latest “full sim” is Compared to Cammin [ATL-PHYS-2003-024] • Applied same cuts as Cammin and saved v00-01-05 • On the whole encouraging. • Problem with ttjj • many events had >=4 unique b-quarks • Had to remove them, as ttjj(jj=bb)  ttbb

  7. Signal and BG Efficiencies. higher jet mult. in MC@NLO? 25% 47% cut on 2 tops too harsh? 15% 30% 17% 47% • Latest “full sim” is Compared to Cammin [ATL-PHYS-2003-024] • Applied same cuts as Cammin and saved v00-01-05 • On the whole encouraging. • Problem with ttjj • many events had >=4 unique b-quarks • Had to remove them, as ttjj(jj=bb)  ttbb

  8. Moving on..... • Look at signal and BG normalised to 30 fb-1 • Problem: BG samples not big enough! Use AF? • No sensible distributions yet! – Can’t do shape analysis!

  9. Optimisations/Cuts.. • Lots of cut optimisations to consider; also new cuts like Pt(J12+J22)>75 GeV on bJets forming Higgs • I will add this cut to the CVS-based analysis

  10. A Cut: Pt(J12+J22)>70 GeV on bJets forming H • Red circles: signal (+ black dot = “correct” bjets). • Others: backgrounds #5855 ttbb[QCD] #5340 poslep #5341 neglep Pt J1 Pt J1 Pt J1 Pt J2 Pt J2 Pt J2 #5214 ttbb[EW] #5212 ttjj

  11. “Higgs bJets”: order by bjetWeight • Currently, analysis in CVS produces Higgs from highest Et bJets if >2 remain after t/tbar. • Tried using bjetWeight to order the jets if >2 “left over”. • No difference really, as most (~99%) of the selected events have only 2 bJets! • we have to improve how we reconstruct the tops to beat combinatorics!

  12. Common Analysis: things I don’t like... • Removal of ttjj where jj=bb • Truly awful to devise algorithm to do this in tthhbbClass.cxx (!) • Settled on removing events with 4 or more UNIQUE TRUTH b-quarks in ttjj. • Typical Herwig b->bMeson->b: check mother, grandmother etc. to see if b is unique • We also see eg: b-g-g-g-g-g-bbar where ‘b’ is mother of ‘bbar’, and ‘b’ has no mother. • Output ntuple ‘improved-data’ has a new attribute to allow one to remove these events for ttjj: “my_truthUniqueBQuarks” (remove ttjj event if >=4). • doplots.C is a root macro in CVS and cuts out these events • runtth.sh makes 10 ntuples for samples 5212 • the list of input files is too large for my shell (zsh) • these have to be merged manually into “5212All.root” • merge: TChain ch("improved-data");ch.Add("5212*.root");ch.Merge("5212All.root"); • top-mass window seems too harsh. • jet calibration.. is it even done??

  13. Other things to implement • Add soft muons(+n??) back to Jets. • Jet energy corrections based on v12. • See if there’s any way of improving combinatorics. • D=0, instead of colinear solution. • Improve Whad light jets (use 3+ jets?- Simon?). • S/BG discrimination with Neural Net (Helen). • Bill’s fitting code. • Others people would like to see / I have forgotten?? • Volunteers????? • Not enough events for a BG shape analysis.

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