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

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

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

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

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

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

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

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, 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

Back Up

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

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 -

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) (%) 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

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, 112002 (2005) PYTHIA-Tune A provides a proper modeling of the underlying event contributions