status of nlojet++ for dijet angular distributions
DESCRIPTION
Status of NLOjet++ for dijet angular distributions. Lee Pondrom 20 April 2010. Ingredients. 1.1 fb -1 jet100 triggered data 1E10 nlojet++ events with CTEQ6 2E6 Pythia events with full CDFSim and CTEQ5 1E6 ‘standalone’ Pythia events with CTEQ6 and ISR, FSR turned off. Pythia first. - PowerPoint PPT PresentationTRANSCRIPT
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Status of NLOjet++ for dijet angular distributions
Lee Pondrom
20 April 2010
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Ingredients
• 1.1 fb-1 jet100 triggered data
• 1E10 nlojet++ events with CTEQ6
• 2E6 Pythia events with full CDFSim and CTEQ5
• 1E6 ‘standalone’ Pythia events with CTEQ6 and ISR, FSR turned off.
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Pythia first
• We have to use Pythia to correct the data to the hadron level.
• We use a calculation of the subprocess cross sections to understand Pythia.
• We learn that to reproduce the Pythia angular distributions, the 2->2 subprocesses with nonidentical final state partons must be u<->t symmetrized.
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22 symmetrized jet_chi cross sections
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Key to previous slide
• q1q2->q1q2 t channel gluon exchange• q1q2bar->q1q2bar t channel gluon• q1q1->q1q1 t channel gluon• q1q1bar->q2q2bar s channel annihilation• q1q1bar->q1q1bar s and t channels• q1q1bar->glueglue s channel annihilation• glueglue->glueglue/q1q1bar s and t • q1glue->q1glue compton
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2->2 subprocesses
• The peaks at =1 come from the u<->t symmetrization
• The t channel gluon exchange cross sections dominate, which is the motivation for the choice of scale Q2=pT
2.
• Now that we understand Pythia born, let us look at nlojet++ born
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2->2 Pythia compared to nlojet born and jet_chi
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Normalization
• Each set of four mass plots has one overall normalization.
• All programs agree on the 1/mass4 dependence of the cross section.
• Nlojet++ born agrees better with Pythia as the mass increases.
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conclusion
• We understand Pythia. It agrees well with the data, and strengthens the Pythia based quark substructure analysis.
• To compare nlojet++ to the data, we need to correct the data to the hadron level using Pythia
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Nlojet++ has no CDF trigger
• After jet energy corrections the 100 GeV trigger moves to about 120 GeV
• ET= M/(1+)=(Msin(*))/2 which has to be removed, in addition to other instrumental effects.
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120 GeV trigger threshold cut in the angular distribution
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correct the data to the hadron level using Pythia MC
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Corrected data agree well with hadron level Pythia Q2=pT
2
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2 for hadron level data compared to Q2=pT
2 Pythia noqsub
• 20 bins one parameter fits
• Mass 2
• 600 GeV 32
• 700 GeV 38
• 800 GeV 17
• 900 GeV 17
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2 fits to quark substructure 600 GeV mass
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2 fits to quark substructure 700 GeV mass
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2 fits to quark substructure 800 GeV mass
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2 fits to quark substructure 900 GeV mass
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summary
• Mass bin noqsub 2 TeV 3 TeV 2
• 600 GeV 22.7 20.1 22.9
• 700 GeV 32.8 20.0 44.3
• 800 GeV 16.4 58.3 7.5
• 900 GeV 13.4 29.2 33.8
• No clear pattern
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Run nlojet++ 1010 events 0=ETavge
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Vary 0 in NLOjet++
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Fit nlojet++ to hadron level data
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2 for one parameter fits to first 12 bins of data with nlojet++
• Mass GeV 0=Etav 0.7Etav 1.4Etav• 600 75 110 78• 700 75 48 65• 800 36 48 35• 900 37 35 37
• No fit is particularly good, compared to Pythia
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ETave compared to mjj These two scales were fit to the data in Pythia
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Compare lo and nlo 0=ETaveK factor 1.1
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Compare lo and nlo 0=mjj
K factor 1.44
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2->2 born level calculations, Pythia
• Pythia ‘stand alone’. 1E6 events• All initial and final radiation turned off:
mstp(61)=mstp(71)=mstp(81)=mstp(111)=0. No CDFSim. Q2=pT
2 mstp(32)=2.• QCD processes msub(381)->msub(386)
switched on.(qq->qq etc).• Ckin(1)=400, ckin(3)=90, lower limits on ŵ,
and on pT . Same cuts in the main CDF MC.
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Cuts in nlojet++
• For 2 partons with highest ET
• ET>10 GeV
• ||<2
• Cone size D=0.7 in (,) space
• Rsep = 1.3. D and Rsep govern when the third parton is included with one of the other two to form a ‘jet’. Should have no effect on a born calculation.
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2->2 and full Pythia compared
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Conclusions from this exercise
• 2->2 Pythia and full Pythia at the parton level look the same. ISR and FSR have little effect.
• Hadron level Pythia looks like the data.
• Nlojet++ born does not agree with 2->2 Pythia.
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Status
• The large K factor for mjj is reason to be suspicious of the accuracy of the nlo calculation for that scale.
• Etave has a more modest scale differece between lo and nlo calculations.
• Pythia fits the data better than nlojet++• I have not achieved as good a limit on
quark substructure using hadron level Pythia or nlojet++.
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