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

2. 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 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

3. gluon PDF at high-x not well known
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

4. Jet cross sections with kT algorithm
Results |yJet | <2.1
Good agreement with NLO pQCD

5. Data/NLO
Measurements in the forward region will contribute to a better understanding of the gluon PDF

6. UE/Hadronization corrections
For comparison to NLO pQCD calculations corrections have to be applied for Underlying event and Hadronization effects
jet
Calorimeter level
Hadron level
Parton level
At low pT the correction is ~20% and it is negligible above 200 GeV/c

7. 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

8. Summary & Conclusions
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
CDF publication for central jets with 385 pb-1
Phys. Rev. Lett.96, (2006)
CDF publication for central + forward jets with 1 fb-1
Submitted to Phys. Rev. D, hep-ex/ (2007)
CDF also performed the measurement using the Midpoint conebased algorithm
Phys. Rev. D 74, (R) (2006)
These measurements will contribute to a better understanding of the gluon PDF inside the proton

9. Back Up

10. kT algorithm
Separate jets according to their relative transverse momentum
Compute for each pair (i,j) and for each particle (i) the quantities:
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)
Iterate until all particles are in jets

11. Previous results with kT algorithm
Inclusive Jet Cross Section at Tevatron (Run I)
jet
In pp colliders the undelying event contribution is important
Photoproduction at HERA
jet -

12. 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”)
 % 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/

13. CDF publication: Phys. Rev. D71, 112002 (2005)
MC modeling
Jet Shape measurements
Test of parton shower models å = Y
jets T R P r N ) , ( 1
Sensitive to the underlying event
CDF publication: Phys. Rev. D71, (2005)
PYTHIA-Tune A provides a proper modeling of the underlying event contributions