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FxFx merging in tt+(up to) 2jets with aMC@NLO in PYTHIA8

FxFx merging in tt+(up to) 2jets with aMC@NLO in PYTHIA8. J. Fernandez (with many thanks for the comments and prompt answer from Josh Bendavid). Setup and settings (I). pp>t t~ +0,1,2j @13TeV generated in separated multiplicity samples (100k events each) using aMC@NLO v2.1.1 (No PS):

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FxFx merging in tt+(up to) 2jets with aMC@NLO in PYTHIA8

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  1. FxFx merging in tt+(up to) 2jets with aMC@NLO in PYTHIA8 J. Fernandez (with many thanks for the comments and prompt answer from Josh Bendavid)

  2. Setup and settings (I) • pp>t t~ +0,1,2j @13TeV generated in separated multiplicity samples (100k events each) using aMC@NLO v2.1.1 (No PS): • With FxFx merging option (ickkw=3) • With NO merging option (ickkw=0) • Same options for the rest: • Running options: • cteq6_m = pdlabel ! PDF set • average = event_norm ! Normalize events to sum or average to the X sect. • F = fixed_ren_scale ! if .true. use fixed ren scale • F = fixed_fac_scale ! if .true. use fixed fac scale • 4 = maxjetflavor • PYTHIA8 = parton_shower ! PS set to OFF in any case • Jets options: • 1 = jetalgo ! FastJet jet algorithm (1=kT, 0=C/A, -1=anti-kT) • 0.7 = jetradius ! The radius parameter for the jet algorithm • 10 = ptj ! Min jet transverse momentum • -1 = etaj ! Max jet abs(pseudo-rap) (a value .lt.0 means no cut) J. Fernández

  3. Setup and settings (II) • Hadronized with PYTHIA8 (interfaced through CMSSW_7_1_0_pre7) • Script provided by Josh Bendavid • Key parameters: • 'JetMatching:coneRadius = 1.', • 'JetMatching:qCut = 30.', • 'JetMatching:qCutME = 10.', • 'JetMatching:nQmatch = 4', • 'JetMatching:nPartonsNow = 0', # 1 for 1j, 2 for 2j • 'TimeShower:nPartonsInBorn = 2', # 3 for 1j, 4 for 2j • 'JetMatching:nJetMax = 1‘ #2 to merge 0j+1j+2j J. Fernández

  4. Some numbers • *Generation time on a dedicated 32-core multiCPU Xeon. In addition grid process time must be added… • - Xsec values do not match those from Table 5 of arXiv:1405.0301v1 (sameptjvalue?) • - Many problems running t t + 2j NNLO: 359 subprocesses, some (residual) subprocesses getting stuck over and over, and crashing after 16h… (P0_gg_ttxgg/GF62, P0_gg_ttxgg/GF61, P0_gg_ttxgg/GF22). Need them all successfully completed in order to merge properly the full result… J. Fernández

  5. Caveats for plots • Gen Jet: any Jet AK4 • Radiated Jet: any Gen Jet not matched (dR<0.1) to any top decay product • qCut = 30 GeV • Two validation checks: • FxFx merging vs Born level contributions • FxFx merging vs NoFxFx (simple adding of histograms according to weights) • Normalization required to compare same scales J. Fernández

  6. 1 jet Max comparison J. Fernández

  7. Total number of jets (1jmax) FxFx FxFx NoFxFx NoFxFx J. Fernández

  8. Radiated pT>10 jets & pT>30 FxFx FxFx 1j 2j NoFxFx NoFxFx J. Fernández

  9. 1st and 2nd leading jets FxFx FxFx NoFxFx NoFxFx J. Fernández

  10. 1st and 2nd radiated jets FxFx FxFx 30GeV 30GeV NoFxFx NoFxFx J. Fernández

  11. 3rd and 4th leading jets FxFx FxFx NoFxFx NoFxFx J. Fernández

  12. 3rd and 4th radiated jets FxFx FxFx NoFxFx NoFxFx J. Fernández

  13. Normalized FxFx vs NoFxFx FxFx FxFx NoFxFx NoFxFx J. Fernández

  14. Normalized FxFx vs NoFxFx FxFx FxFx NoFxFx NoFxFx J. Fernández

  15. Questions • 0.7 = jetradius ≠ 'JetMatching:coneRadius = 1.‘ • aMC@NLO seems to force it to 1. when FxFx is enable in a warning message but LHE file keeps the 0.7 value • Grid pack working in 7XY? Using code from aMC@NLO independent of CMSSW for the moment • LHAPDF interface, full or lite? • CPU time in tt +2j? • If SIM&RECO CMSSW step fails for some events, are the weights still valid? • Should use sum = event_norm instead? • Differences in xsec obtained wrt those in Table 5 of arXiv:1405.0301v1 • Cross/section dependes on parton_shower/ickkw parameters? J. Fernández

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