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Inclusive Jet Cross Section at CDF

HRPN-CT-2002-00292 E.U. Research Training Network Probe for New Physics. Inclusive Jet Cross Section at CDF. Régis Lefèvre IFAE Barcelona on behalf of the CDF Collaboration. HEP-EPS 2005 International Europhysics Conference on High Energy Physics July 21 st -27 th 2005, Lisboa, Portugal.

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Inclusive Jet Cross Section at CDF

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  1. HRPN-CT-2002-00292 E.U. ResearchTraining Network Probe for New Physics Inclusive Jet Cross Section at CDF Régis Lefèvre IFAE Barcelona on behalf of the CDF Collaboration HEP-EPS 2005 International Europhysics Conferenceon High Energy Physics July 21st-27th 2005, Lisboa, Portugal

  2. Outline • Introduction • Tevatron • CDF • Motivations • Cone Jet Algorithms and pQCD • KT Algorithm • Framework - Related Topics • Underlying Event • Jet Shapes • Jet Energy Scale • Results • Inclusive Jet Production Cross Section using the KT Algorithm • Inclusive Jet Production Cross Section using the Midpoint Algorithm • Conclusion and Outlook Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  3. Tevatron • Proton-antiproton collisions • s = 1.96 TeV (Run I  1.8 TeV) • 36 bunches: 396 ns crossing time • Peak luminosity ~ 1032 cm-2 s-1 • Weekly integrating 12 to 20 pb-1 • About 1.1 fb-1 delivered Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  4. CDF • Highly upgraded for run II • New silicon tracking • New drift chamber • Upgraded muon chambers • New plug calorimeters • New TOF • Data taking efficiency ~ 85 % • About 0.9 fb-1 on tape • Analysis based on 385 pb-1 Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  5. CTEQ4M PDFsCTEQ4HJ PDFs Run I CDF Inclusive Jet Data(Statistical Errors Only)JetClu RCONE=0.7 0.1<||<0.7R=F=ET /2 RSEP=1.3 Motivations • Legacy from Run I • Great interest on apparent excess at high ET • SM explanation: increased gluon PDFat high x • New PDFs from global fit including CDF/D0 high ET data (CTEQ6, MRST2001) • Stringent test of pQCD • Over ~ 8 order of magnitudes • Tail sensitive to New Physics • Probing distances ~ 10-19 m • PDFs at high Q2 & high x • Enhanced cross section thanks to new s Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  6. below threshold (no jets) above threshold (1 jet) Cone Jet Algorithms and pQCD • Infrared and Collinear Safety • Fixed order pQCD contains not fully cancelled infrared divergences • Inclusive jet cross section affected at NNLO • Run I Cone Algorithm: JetClu • Neither infrared nor collinear safe • Run II Cone Algorithm: Midpoint • Uses midpoints between pairs of proto-jets as additional seeds  Infrared and collinear safety restored • Merging/Splitting • NLO pQCD uses larger cone radius R’=RRSEPto emulate experimental merging/splitting • Arbitrary parameter RSEP: prescription RSEP=1.3 (based on parton level approximate arguments) Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  7. KT Algorithm • Inclusive KT algorithm • Merging pairs of nearby particles in order of increasing relative pT • D parameter controls merging termination and characterizes size of resulting jets • PT classification inspired by pQCD gluon emissions • Infrared and Collinear safeto all orders in pQCD • No merging/splitting • No RSEP issue comparing to pQCD • Successfully used at LEP and HERA • Relatively new in hadron collider • More difficult environment • Underlying Event  Multiple Interactions per crossing (MI) Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  8. Framework - Related Topics • Central jets: 0.1 < |y| < 0.7 • Midpoint: RCONE = 0.7, fMERGE = 75% • KT: D = 0.5, 0.7 and 1.0 • To make sure that Underlying Event and MI contributions are well under control • Data fully corrected to hadron level • Requires a good simulation of the detector • Requires a Monte-Carlo generator able to reproduce the Jet Shapes • Jet fragmentation and parton cascades • NLO pQCD corrected to hadron level • Parton level pQCD calculation correctedfor the Underlying Event and Hadronization • Requires a Monte-Carlo generator able to reproduce the Underlying Event Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  9. Underlying Event • Everything but the hard scattering process • Initial state soft radiations • Beam-beam remnants • Multiple Parton Interactions (MPI) • Studied in the transverse region • Leading jet sample • Back-to-back sample Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  10. Energy Flow Inside Jets Jet shapes governed by multi-gluon emission from primary parton • Test of parton shower models • Sensitive to underlying event structure • Sensitive to quark and gluon mixture in the final state hep-ex/0505013(Accepted by PRD) (1-) 37 < pT < 380 GeV/c Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  11. Jet Energy Scale • Central calorimeter response very well reproduced by the simulation • Absolute Calibration • E/p of isolated tracks used to tune the showering simulation (G-Flash) • Residual discrepancies taken as systematic errors • E/p depends on E (non compensated calorimeters): reasonable simulation of the pT spectrum of the particles within a jet by PYTHIA and HERWIG fragmentation models • Induced difference on Jet Energy Scale < 1% • Photon-jet balance • Data and Simulation agreeat 1% to 2% level • Non uniformity versus  • Dijet balance • Resolution • Bisector method Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  12.  (Hadron Level with MPI) CHAD =  (Parton Level without MPI) Jet Production with KT • NLO pQCD corrected to hadron level using PYTHIA-Tune A • Good data-theory agreement • Over ~ 8 orders of magnitude • PT reach extended by ~ 150 GeV/c with respect to Run I • Experimental uncertainty dominated by jet energy scale • 6% luminosity uncertaintynot included in the plots • Theoretical error dominated by PDFs • Gluon at high x Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  13. KT jets versus D D = 0.5 D = 0.7 D = 1.0 Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  14. Jet Production with Midpoint Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

  15. Conclusion and Outlook • Good agreement with pQCD using both KT and Midpoint • Stringent test of pQCD over ~ 8 orders of magnitude • PT reach extended by ~ 150 GeV/c with respect to Run I • Careful treatment of non perturbative effects • KT study done with 3 different values of the D parameter • Underlying Event and MI contributions seem to be well under control • To be used in future PDF global fits in order to better constrain the gluon PDF at high x • Outlook • Measurements done with 1 fb-1will come soon • Inclusive forward jets productionmeasurement expected soon • Further constrain the PDFs • Search for contact interactions comparing central and forward jet production rates Régis Lefèvre, HEP-EPS 2005, July 21st 2005, Lisboa, Portugal

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