Single top efficiencies with pileup

1
Single top efficiencieswith pile-up

• Marcello Barisonzi
• Zdenko van Kesteren

2
Samples

• Sample single top (t-chan) events
• no background
• ?Br 54.2 pb
• AOD events, full simulation
• At low luminosity and high luminosity
• with pile-up
• 85k low luminosity (1.6 fb-1)
• 33k low luminosity with pile-up (0.6 fb-1)
• Broken sample muons are not reconstructed
• in pile-up sample

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Program

• Can we use the same analysis on pile-up sample as
  on the sample without?
• Forward jet selection, pTgt50, ?gt2.5
• Isolated lepton, pTgt20 GeV
• One identified b-jet, pTgt50 GeV
• How do the efficiencies differ?
• How do kinematic variables change?
• multiplicities
• jet scale, pT spectrum
• top mass

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Total ET and missing ETbefore pre-selection
Without pile-up With pile-up
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Multiplicities
Njet-lightcone size 0.4
Nb-jet cone size 0.4
Electron multiplicity
Without pile-up With pile-up
Njet-lightcone size 0.7
Nb-jet cone size 0.7
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pT spectra
Leading b-jet Second b-jet cone size 0.4
Light jet cone size 0.4
Leading b-jet Second b-jet cone size 0.7
Light jet cone size 0.7
Cone size 0.4 ? 2 GeV Cone size 0.7 ? 5 GeV
Shift in pT observed pile-up adds energy in jet
cone
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Massplots
mtop 174.6 1.1 GeV
mtop 177.2 1.6GeV
?mtop ? 2.6 GeV (2.5 ?)
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Efficiencies
9
Conclusions

• Data is broken (absence of muons in pile-up
  sample)
• First look at pile-up in single top
• Efficiencies comparable for both samples
• Slight increase in light jet multiplicity in
  pile-up sample observed
• Spectra of jets
• Ljets slight increase for low pT
• bjets increase in average energy
• Reconstructed top mass slightly larger in pile-up
  sample
• Detailed study of pile-up requires larger MC
  statistics