In situ calibration: status of ? jet and Z jet

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In situ calibration status of ?jet and Zjet

• Outline
• Introducrtion
• ?jet status
• Zjet reminder
• Conclusions and future work

S. Jorgensen IFAE
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Introduction

• Motivations
• ? and Z0 are well calibrated objects at EM scale
  balancing the recoiling hadronic system
• potentially large statistics available
• pT range from 20 GeV to 60 GeV
• Z(?ll)jet (2Hz)
• ?jet ( 0.1 Hz)
• reserving 1Hz for downscaled trigger
• pT range gt 60 GeV
• ?jet (2Hz)
• Zjet ( 0.1 Hz)
• Issues to be understood
• Detector effects response, showering
• Physics effects fragmentation, gluon radiation
  (multijets)
• Compare different methods of analyses and the two
  data samples

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?jet 1 pT balance

• Rome data. Athena 10.0.1
• select gamma
• select highest pT jet
• apply phi back-to-back cut

? pT
Parton pT
pT balance (pT parton pT photon)/ pT
photon Fit peak region iterating a gaussian fit
between s around the most probable value
http//agenda.cern.ch/fullAgenda.php?idaa057453
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?jet 2 pT balance

• Biases on pT for the different jet algorithms

Algorithms Cone 0.7 Cone 0.4 Kt
Parton level 1 - 0 1 - 0 1 - 0
Recon level 2 - 0 15 - 7 10 - 2
To understand differences Cone7 and kT, study
underlying event, min.bias noise, etc
Standard H1 weighting calibrated for the C7
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?jet 3 UE

• Want to find the mean Et for EU. We look to the
  transverse region of the event avoiding 60
  degrees on both sides of photon and jet
  (suggested by the standard model group)

60o
Protojet recon lvl
Protojet particle lvl
Tower
Et (MeV)
Et (MeV)
Et (MeV)
Mean transverse energy

Tower 15.1 0.2 MeV
Recon protojet towers after applying noise supression 15.8 0.2 MeV
Particle protojet particles in one tower 19.1 0.4 MeV
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?jet 4 Jet size

• Jet constituent Et versus deltaR (const R jet
  R) (one entry per tower)

C7
Kt
C4
Et (GeV)
Particle level
deltaR
deltaR
deltaR
C4
Et (GeV)
Recon level
deltaR
deltaR
deltaR
Why is the size so big?
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?jet 5 Jet size

• Jet constituent Et density versus deltaR
  (integrated Et in a 0.1 ring and divided by the
  area)

C7
Kt
C4
Et (GeV)
Particle level
deltaR
deltaR
deltaR
Et (GeV)
Recon level
deltaR
deltaR
deltaR
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• ?jet 6 Dijet background

Default CBNT cuts S/B10 Optimised
cuts S/B30 Efficiency ? 90
Efficiency ? 15
low pT sample ltETgt30 GeV
Data sample Athena 7.2.0 DC1 data
Mean (-0.6, 0.6) window Cone 0.4 Cone 0.7 kT
Signal -13 0.8 2 0.9 1 0.9
Background -15 2 1 2 -1 2
remaining jet background p0
statistical error
C. Deluca. Rome Workshop
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• Zjet Relative calibration across the detector
  at HAD scale

pTbalance calibrated jets
Z??e?e?
hlt2.5
Calibration or Reconstruction problem for h gt
2.5 ? More study needed.
hgt2.5
Data sample Rome Athena 10.0.1
J. Proudfoot. Rome Workshop
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• Zjet Relative calibration across the detector
  at EM scale

Z??e?e?
pTbalance
Jet response (Etmiss projection)
10.0.1 Rome
??jet?
??jet?
(E?)
(E? ?????? ?)

• see dips at eta 1.5 and 3.2, and perhaps 0.8
• Expected from particle-level comparisons (F.
  Paige/S. Padhi)
• Pt balance flatter in eta
• E (and Response) is increasing with ? both R
  and balance see this
• out-of-cone showering also increases with eta
  only balance sees that effect ? cancels higher
  response giving flatter balance

B. Kehoe. Rome Workshop
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• Methods to Study Jet Energy Scale

• Pt balance
• Calculated from leading jet and photon/Z
• Sensitive to out-of-cone showering, underlying
  event, gluon radiation in addition to detector
  effect
• Need to disentangle different effects
• Etmiss Projection
• Etmiss (vector sum over everything in
  calorimeter)
• Sensitive to particle response only
• not effects from algorithm applied to recoil
• For further information on this method see Doug
  Schoutens talk

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• Comparing Z and ?

Z??e?e?
Compared with ? Offset of approx. 0.05 relative
to Zjet
Z??e?e?Balance -0.109 Z?????? Balance -0.111
Statistical error 0.3
J. Proudfoot. Rome Workshop
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Future work

• Conclusions
• These events are useful to compare the different
  jet algorithms
• And to do the relative energy calibration through
  the detector
• Ultimately would provide useful information on
  absolute energy calibration
• Future work
• Continue studies on both gammajet and Zjet
  events and chech the agreement between them
• Continue EU studies
• More diagnostic of the jet algorithm behaviour at
  recon level
• Use different datasets with different level of
  underlying events to help understand the
  difference of Kt and C7 algorithms
• See how this affects the pT balance for different
  energies