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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)