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

in PYTHIA8J. 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):A. With FxFx merging option (ickkw=3)

B. 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)

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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

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Some numbersProcess NNLO

Xsec (pb)

Frac Neg

weights

Matching Eff 1jmax

Effective Xsec(pb)

Matching Eff 2jmax

Effective Xsec(pb)

Gen CPU time*

tt0j FxFx 693.0 0.25 0.26 244.7 0.26 244.7 1h

tt1j FxFx 746.4 0.39 0.50 485.2 0.27 262.9 6.5h

tt2j FxFx 600.7 >24h

tt0j NoFxFx

652.3 0.25 - - - - <1h

tt1j NoFxFx

715.4 0.40 - - - - 5.6h

tt2j NoFxFx

656.4 0.41 - - - - >24h

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*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 (same ptj value?)

- 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…

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

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1 jet Max comparison

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Total number of jets (1jmax)

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FxFx FxFx

NoFxFxNoFxFx

Radiated pT>10 jets & pT>30

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FxFx FxFx

NoFxFxNoFxFx

2j 1j

1st and 2nd leading jets

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FxFx FxFx

NoFxFxNoFxFx

1st and 2nd radiated jets

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FxFx FxFx

NoFxFxNoFxFx

30GeV 30GeV

3rd and 4th leading jets

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FxFx FxFx

NoFxFxNoFxFx

3rd and 4th radiated jets

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FxFx FxFx

NoFxFxNoFxFx

Normalized FxFx vs NoFxFx

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FxFx FxFx

NoFxFxNoFxFx

Normalized FxFx vs NoFxFx

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FxFx FxFx

NoFxFxNoFxFx

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?

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