Inclusive Jet Cross Section Measurement at CDF

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 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

3. 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. jet jet 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

7. kT Jetsvs 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-1of 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, 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

9. Back Up

10. Compute for each pair (i,j) and for each particle (i) the quantities: • Starting from smallest {dij ,di}: • - If it is a dithen it is called a jetand is removed from the list • - If it is a dijthe particles are combined in “proto-jets”(E scheme) • Iterate until all particles are in jets kT algorithm • Separate jets according to their relative transverse momentum

11. jet jet jet jet jet jet 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 -

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”)  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: *** extracted from hep-ex/0510047

13. 1 P ( 0 , r ) å Y = T ( r ) N P R ( 0 , ) jets jets T 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