Brian Cox Rencontres de Vietnam August 2004

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5th Rencontres de Vietnam, August 5th - 11th
2004
Jet Physics at 2 TeV
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Jet Physics at the Tevatron

• Compared to HERA -
• lower x at same Q2
• higher Q2 at high x

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Sensitivity to PDFs - a look back at Run I
gq subprocess factor of 2 increase from CTEQ4M -
CTEQ4HJ
Only flexibility is in the high-x gluon - led to
CTEQ4HJ pdfs with greater statistical weight
given to the Tevatron high ET jet data
Stump et. al. JHEP 0310046,2003
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Run II inclusive jet cross sections from CDF
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The Kinematics of Jet Production at Tevatron
Central (y0)
Forward (y2)
ET200 GeV
ET400 GeV
ET200 GeV
ET100 GeV
Stump et. al. JHEP 0310046,2003
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Inclusive Jet cross sections binned in rapidity

• no disgreement but large errors - larger pdf and
  energy scale uncertainties in forward region
• working hard to reduce energy scale uncertainty
  in forward region

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Dijet Cross Sections
Consistent with inclusive jet cross sections
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From PDFs to the Final State
Inclusive and dijet cross sections
Azimuthal decorrelations and jet substructure
Thanks to Markus Wobisch
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Dijet Azimuthal Decorrelations
Df distribution directly sensitive to higher
order QCD radiation without requiring 3rd jet to
be found
Thanks to Markus Wobisch again
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Dijet Azimuthal Decorrelations
Increasingly peaked at p as pT increases
Untuned pythia significantly different from
HERWIG and data - more ISR improves matters
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Jet Substructure
Fraction of transverse momentum outside inner
cone r 0.3
Well described by PYTHIA tune A (sensitive to
underlying event structure as well as quark /
gluon initiator parton and parton showering
models)
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Summary
More luminosity, higher invariant mass reach,
more sophisticated jet algorithms, ongoing
understanding of jet energy scale -gt RunII jet
physics is well underway