Inclusive Jet Cross Section Measurement at CDF
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Transcript of Inclusive Jet Cross Section Measurement at CDF
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Inclusive Jet Cross Section Inclusive Jet Cross Section Measurement at CDFMeasurement at CDF
Olga Norniella
IFAE-Barcelona
CDF
On behalf of the CDF Collaboration
La Thuile Tuesday 20th 2007
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Testing the Standard Testing the Standard ModelModel
• Over 8 orders of magnitude
• Probes distances up to 10-19 m
• Tail sensitive to New Physics
• Stringent test of pQCD
Measure inclusive jet cross section
Precise search algorithm is necessary to compare with theory
• Infrared/collinear safe to all orders in pQCD
• No merging/splitting procedure No Rsep parameter is needed for comparison to pQCD
• Higher jet with respect to Run I• Increased pT range for jet production
• kT algorithm is preferred by theory
• Separate jets according to their relative transverse momentum
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2,2
,2 ),min(
DR
ppd jTiTij
2
, )( iTi pd
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Constraining the PDFs
Measurements in the forward region allow to constrain the gluon PDFs
gluon PDF at high-x not well known
Measurements in the forward region are important
• Sensitive to PDFs
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Jet cross sections with kT
algorithm
Good agreement
with NLO pQCD
Results |yJet | <2.1
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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 UE/Hadronization correctionscorrections
At low pT the correction is ~20% and it is negligible above 200 GeV/c
For comparison to NLO pQCD calculations corrections have to be applied for Underlying event and Hadronization effects
Calorimeter level
Hadron level
Parton level
jet
jet
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kT Jets vs D2
2,2
,2 ),min(
DR
PPd jTiTij
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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Inclusive jet cross section measured using ~1fb-1 of CDF Run II data in five rapidity regions (up to |YJet | <2.1 )
• 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
Summary & Conclusions
• 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)
These measurements will contribute to a better understanding of the gluon PDF inside the proton
CDF also performed the measurement using the Midpoint conebased algorithm
Phys. Rev. D 74, 071103(R) (2006)
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Back Up
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kT algorithm
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2,2
,2 ),min(
DR
PPd jTiTij
2
, )( iTi Pd
1. Compute for each pair (i,j) and for each particle (i) the quantities:
2. Starting from smallest {dij ,di}: - If it is a di then it is called a jet
and is removed from the list - If it is a dij the particles are
combined in “proto-jets” (E scheme)
3. Iterate until all particles are in jets
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)
jet
jet
jet
Photoproduction at HERA
-
jet
jet
jet
In pp colliders the undelying event contribution is important
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Correlations on syst. Correlations on syst. uncertaintiesuncertainties
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) (%)
p<12 1.5 ~ 0.76 ~ 0.11
12<p<20 2.5 ~ 0.30 ~ 0.35
P>20 3.5 ~ 0.27 ~ 2.0
*** extracted from hep-ex/0510047
Correlations among systematic uncertainties in different Y and pt jet bins are considered (help for the future use of the data)
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MC modeling
=jets T
T
jets RPrP
Nr
),0(),0(1
)(
)(1 r Jet Shape measurements
• Sensitive to the underlying event
• Test of parton shower models
PYTHIA-Tune A provides a proper modeling of the underlying event contributions
CDF publication: Phys. Rev. D71, 112002 (2005)