Inclusive Jet Cross Section Measurement at CDF

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Inclusive Jet Cross Section Measurement at CDF
Olga Norniella
IFAE-Barcelona
On behalf of the CDF Collaboration
La Thuile Tuesday 20th 2007
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Testing the Standard Model

• Measure inclusive jet cross section

• Stringent test of pQCD

• Over 8 orders of magnitude

• Tail sensitive to New Physics

• Probes distances up to 10-19 m

• Higher ?jet with respect to Run I

• Increased pT range for jet production

• Precise search algorithm is necessary to compare
  with theory

• kT algorithm is preferred by theory

• Separate jets according to their relative
  transverse momentum

• Infrared/collinear safe to all orders in pQCD

• No merging/splitting procedure

• No Rsep parameter is needed for comparison to
  pQCD

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Constraining the PDFs

• Measurements in the forward region are important

• Sensitive to PDFs

gluon PDF at high-x not well known
Measurements in the forward region allow to
constrain the gluon PDFs
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Jet cross sections with kT algorithm

• Results yJet lt2.1

Good agreement with NLO pQCD
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Data/NLO
Measurements in the forward region will
contribute to a better understanding of the gluon
PDF
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UE/Hadronization corrections

• For comparison to NLO pQCD calculations
  corrections have to be applied for Underlying
  event and Hadronization effects

Calorimeter level
Hadron level
Parton level
At low pT the correction is 20 and it is
negligible above 200 GeV/c
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kT Jets vs D
As D increase the measurement is more sensitive
to the underlying event contribution (important
at low pT).
The results show
that the non-perturbative effect corrections are
under control
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Summary Conclusions

• Inclusive jet cross section measured using
  1fb-1 of CDF Run II data in five rapidity
  regions (up to YJet lt2.1 )

• Using the kT algorithm
• Fully corrected to the hadron level
• Good agreement with theory (corrected for UE /
  Hadronization)

• The kT algorithm works fine in hadron colliders

• CDF publication for central jets with 385 pb-1
• Phys. Rev. Lett.96, 122001 (2006)

• CDF publication for central forward jets with
  1 fb-1
• Submitted to Phys. Rev. D, hep-ex/701051
  (2007)

CDF also performed the measurement using the
Midpoint conebased algorithm
Phys. Rev. D 74, 071103(R) (2006)

• These measurements will contribute to a better
  understanding of the gluon PDF inside the proton

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Back Up
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kT algorithm

• Separate jets according to their relative
  transverse momentum

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Previous results with kT algorithm

• Inclusive Jet Cross Section at Tevatron (Run I)

In pp colliders the undelying event contribution
is important

• Photoproduction at HERA

-
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Correlations on syst. uncertainties

• Correlations among systematic uncertainties in
  different Y and pt jet bins are considered (help
  for the future use of the data)

• An appendix in the PRD includes the
  decomposition of the absolute JES uncertainty
  (according to A. Bhatti et al., Nucl. Instrum.
  Methods A 566, 375 (2006), Determination of the
  Jet Energy Scale at the Collider Detector at
  Fermilab)

? 1.82 on the JES independent of pTjet
coming from
0.5 uncertainty from calorimeter stability
1.0 uncertainty due to the modeling of the
jet fragmentation
0.5 uncertainty from simulation of the EM
calorimeter response
1.3 uncertainty from simulation of the
calorimeter at the boundary
? Description of the calorimeter response to
hadrons
Hadron p range (Gev/c) Uncertainty on e/p () JES uncertainty (lowest pt jet) () JES uncertainty (highest pt jet) ()
plt12 1.5 0.76 0.11
12ltplt20 2.5 0.30 0.35
Pgt20 3.5 0.27 2.0
extracted from hep-ex/0510047

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MC modeling

• Jet Shape measurements

• Test of parton shower models

• Sensitive to the underlying event

CDF publication Phys. Rev. D71, 112002 (2005)
PYTHIA-Tune A provides a proper modeling of the
underlying event contributions