Outline

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Jet studies at CDF in Run II
La ThuileFri. Mar. 14, 2003
Rob Snihur University College London for the CDF
collaboration

• Outline
• Motivation
• Inclusive jet cross section
• Dijet mass
• Jet shapes
• Summary

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Motivation

• Tevatron jet factory
• Probe highest energy scales
• Higher vs ? higher s (factor 3 for ET gt 500 GeV)
• Already more jets than in Run I
• Test fixed-order QCD
• look for deviations ? new physics
• Constrain PDFs
• Analyses
• Inclusive jet cross section (counting jets)
• Dijet Mass (bump hunting)
• Jet Shapes Energy Flow

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Tevatron CDF
Upgraded Tevatron at Fermilabvs 1.8 TeV ?
1.96 TeV Higher s(jet)
NLO QCD
s(jet) ratio Run II / Run I

• Collider Detector at Fermilab (CDF)
• New plug calorimeter (1.1 lt h lt 3.6)
• New tracking system
• Upgraded trigger

jet ET (GeV)
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Highest Energy Jets in Run II
Jet 2 ET 546 GeV (raw) hdet -0.30
Jet 1 ET 583 GeV (raw) hdet 0.31

• Run 152507 Event 1222318
• Dijet Mass 1364 GeV (corr)

CDF Run II Preliminary
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Inclusive Jet Cross Section

• Repeat Run I analyses
• Use CDF cone jet algorithm with R 0.7 (JetClu)

• Event selection cuts
• zvertex lt 60 cm

• ? ET lt 1500 GeV

• Require fully efficient trigger
• Apply jet energy corrections (same as in Run I)

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Systematic Uncertainties
Luminosity uncertainty 6
Largest uncertainty
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Corrected Log

• 8 orders of magnitude!
• Highest ET jets ever!

CTEQ 6.1 hep-ph/0303013
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Corrected Linear
CDF Run II Preliminary
JetClu cone R 0.7, vs 1.96 TeV

s ratio Data / CTEQ6.1
CDF data

5 Energy scale uncertainty
CTEQ 6.1 uncertainty
Inclusive jet ET (GeV)
Good agreement (within uncertainties)
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Run II I

• Higher s in Run II due to higher vs
• Many uncertainties cancel in the ratio

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Dijet Mass

• Higher s in Run II due to higher vs
• 3 more bins at high dijet mass!

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Run II I
Consistent with inclusive jet cross section
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Limits
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Jet Shapes
narrow
?(r)
fat
r
Differential jet shape definition
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Data HERWIG
CDF Run II Preliminary

• Narrower jets at high ET low ?
• HERWIG agrees well with data

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Calorimeter vs. tracking
CDF Run II Preliminary

• Use COT tracks with pT gt 0.5 GeV
• Agrees with calorimeter-based shape
• Agrees with PYTHIA

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Energy flows

• Look outside the jet
• Probe the underlying event

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Energy flows
CDF Run II Preliminary
Increasing ??jet
Increasing ?jet
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Summary

• CDF has preliminary measurements in Run II
• Inclusive jet cross section
• Dijet mass
• Jet shapes energy flow
• Higher vs ? more jets at high ET
• Data samples w/ higher statistics than Run I
• Dominant systematic jet E-scale
• General agreement w/ fixed-order QCD calculations
  Monte Carlos

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Outlook

• Reduced systematics
• More data
• Forward jets

• Different jet algorithms
• Other jet analyses
• Dijet angular distribution
• s(b-jet)