The KT Algorithm at D

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The KT Algorithm at DØ

• Veronica Sorin
• Universidad de Buenos Aires

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Outline

• Jet Algorithms
• KT Jet Algorithm at DØ
• Calibration of KT jets
• Physics Analyses
• Summary

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Jet Algorithms

• Parton jet q and g (before hadronization)
• Particle jet final state particles (after
  hadronization)
• Calorimeter jet measured object (after
  calorimeter shower)

Fixed Cone (RunI) KT (Ellis-Soper)
Iterative
Fixed cone of radius R
Overlapping cones split/merge
parameter Sensitivity to soft radiation
Recombination Distance parameter D
Infrared and collinear safe
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KT Algorithm at DØ (RunI)
Input List of preclusters
Is less than ?
Yes
Merge ij
No
Move i to list of jets
Anyleft?
Yes
No

• Produce list of jets

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Jet Momentum Scale Correction
Calorimeter jet
Particle jet

• Offset (O) Ur noise, pileup, multiple
  interactions, underlying event (ue)
• Response (Rjet) Pmeas / Ptrue
• (using transverse momentum balance in g-jet
  events)

No Showering correction (showering losses outside
cone)
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Luminosity dependent
. .
.
N(GeV)
UE(GeV)
3
1
2
1
D1.0
D1.0
30 lt PTlt 50 GeV
30 lt PT lt 50 GeV
h
h
2
1
1
2
Herwig detector simulation Overlayed to random
crossing
Herwig detector simulation Overlayed to
crossing with inelastic interaction
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Rjet Correction
Monte Carlo Closure
Rjet a b ln(Pjet) c ln2(Pjet)
Rjet
0.9
D1 (KT jets)
0.75
0
Pjet (GeV)
0
300
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Jet Structure
Subject Multiplicity (M) for quark and
gluons Test of QCD, discriminating variable to
tag quark jets in the final state
Cone jet
D0 Preliminary
KT jet
Re-run KT algorithm on all 4-vectors merged
into a jet
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Event Shapes
Thrust
Test QCD, Extraction of as , Non-perturbative
corrections
Jet Production (Inclusive Jet Cross Section ,
Sebastian Grinstein )
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Summary

• KT Jet Algorithm has successfully been
  implemented and calibrated at DØ
• Analyses in progress
• Improvements for RunII

Jet Algorithms http//www.physics.niu.edu/blazey/
jet_alg/jet_alg.html