Impact of jet calibration on w polarization studies using tt events with AOD full simulation

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Impact of jet calibration on w polarization
studies using tt events with AOD full simulation
C. Zhu CPPM/SDU

1. Physics motivations
2. Jet precalibration
3. Conclusions

with F. Hubaut, E. Monnier, P. Pralavorio, B.
Resende CPPM
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Motivations measuring polarization property of w
in ttbar semileptonic decay
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W polarization in top decay

• theoretical value of w polarization

Standard Model (Mtop175 GeV) 0.703 0.297 0.000
Longitudinal W (F0)
Left-handed W (FL)
Right-handed W (FR)

• experiment measurement

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Measurement method

• Selection cuts and reconstruction distort the
  parton level distribution
• Use an independent sample to parametrize these
  effects

parton level
Correction function
1/N dN/dcos?
1/weight
Reconstruction and cuts
cos?
1/N dN/dcos?
cos?
cos?
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Jet calibration
Jet energy precalibration

• Performed on all jets
• It tries to move the peak of energy difference
  distribution between reco jets and MC jets to 0
• Btaged jets (weightgt3) and light jets are
  precalibrated separately.

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(No Transcript)
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In situ calibration

• Alpha is limited inside 2s of energy resolution
• Jet resolution is set for each eta range

?lt0.6 0.6lt?lt1.0 1.0lt?lt1.4 1.4lt?lt1.8 1.8lt?lt2.5
4.90.03E 5.60.031E 7.00.04E 8.20.05E 9.30.04E
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W mass after insitu calibration

• events

Mass ( MeV)
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F0, FL,FR measurement systemetic error induced by
bjet miscalibration
F0
FL
FR
Bjet miscalibration ()
Bjet miscalibration ()
Bjet miscalibration ()
Slope of above plot F0 FL FR
45204521 (AOD) jet cone07 0.0019 -0.0031 0.0011
Atlfast 0.0017 -0.0036 0.0018
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data 45204521 (AOD) ( jet cone07) events
359006
Cos(Y)- Cos(Ytrue) Mean of gausian fit s
Without calibration 0.0130 /- 0.0021 0.0836 /- 0.0031
With only pre- calibration 0.0103 /- 0.0020 0.0819 /- 0.0029
With both calibration 0.0085/- 0.0018 0.0846/- 0.0030
events
Cos(Y)- Cos(Ytrue)
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data 4100 (AOD) (jet cone04) events 141042
Cos(Y)- Cos(Ytrue) Mean of gausian fit s
Without calibration 0.0057 /- 0.0028 0.0777 /- 0.0044
With only pre- calibration 0.0080 /- 0.0028 0.0808 /- 0.0045
With both calibration 0.0044 /- 0.0024 0.0763/- 0.0036
events
Cos(Y)- Cos(Ytrue)
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Summary

• Jet energy precalibration and in-situ calibration
  used in W and top polarization analysis.
• Jet energy rescaled up to 3
• Smaller than jet resolution 10
• ? no improvement on Y resolution (but shift
  slightly decreased)
• In situ calibration does not improve angle
  measurement resolution
• Cone7 jet in Toprex data versus Cone4 jet in
  MC_at_NLO data
• ? No improvement on Y resolution
• Future plan Combinatorial background study