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Inclusive Jet Production @ CDF

HRPN-CT-2002-00292 E.U. Research Training Network Probe for New Physics. Inclusive Jet Production @ CDF. Régis Lefèvre IFAE Barcelona on behalf of the CDF Collaboration. QCD 06 Montpellier, France July 3 rd -7 th 2006. The Tevatron in Run II. Proton-antiproton collisions

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Inclusive Jet Production @ CDF

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  1. HRPN-CT-2002-00292 E.U. ResearchTraining Network Probe for New Physics Inclusive Jet Production @ CDF Régis Lefèvre IFAE Barcelona on behalf of the CDF Collaboration QCD 06 Montpellier, France July 3rd-7th 2006

  2. The Tevatron in Run II • Proton-antiproton collisions • s = 1.96 TeV • 36 bunches: crossing time = 396 ns • Peak luminosity ~ 1.2 1032 cm-2 s-1 • Collecting ~ 20 pb-1 / week • About 1.6 fb-1 delivered Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  3. 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 1.3 fb-1 on tape • Latest results based on 1 fb-1 Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  4. 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 • Gluon PDF increased at high x • New PDFs from global fit include CDF and D0 jet data from Run I (CTEQ6, MRST2001) • Stringent test of pQCD • Over ~ 8 orders of magnitude • Tail sensitive to New Physics • Probing distances ~ 10-19 m • PDFs at high Q2 & high x • Production enhanced at high pTthanks to new s Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  5. 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, QCD 06, July 3rd 2006, Montpellier, France

  6. The 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-hadron collider • More difficult environment • Underlying Event  Multiple Interactions per crossing (MI) Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  7. Results from ZEUS / D0 Run I D0 Run I • Disagreement at low pT • Suggests Underlying Event not properly accounted for

  8. Framework / Related Topics • Look first at central jets: 0.1 < |y| < 0.7 • Where calorimeter simulation is best • Use 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 particle level • Requires a good simulation of the detector • Monte-Carlo generator should be able to reproduce the Jet Shapes • Jet fragmentation and parton cascades • NLO pQCD corrected to particle level • Parton level pQCD calculation correctedfor the Underlying Event and Hadronization • Requires a Monte-Carlo generator able to reproduce the Underlying Event Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  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, QCD 06, July 3rd 2006, Montpellier, France

  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 Phys. Rev. D 71, 112002 (2005) (1-) 37 < pT < 380 GeV/c Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  11. Calorimeter Response to Jets • (First set electromagnetic scale using Z  e+e-) • Absolute jet energy scale • E/p of isolated tracks used to tune the showering simulation (G-Flash) • Residual discrepancies taken as systematic errors • Induced uncertainty on jet energy scale between 1 and 3% • Reasonable simulation of the pT spectrum of the particles within a jet by PYTHIA and HERWIG fragmentation models (fundamental as non-compensated calorimeters) • Induced difference on jet energy scale < 1% • Photon-jet balance • Data and Simulation agree at 1% to 2% level • Non uniformity versus  • Dijet balance • Relative response known to 0.5% level • Resolution • Bisector method • Jet energy resolutions known within relative uncertainties of few % Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  12.  (hadron level with U.E.) CHAD =  (parton level no U.E.) kT Jets: Published Results • PYTHIA-Tune A used as nominal • HERWIG used for uncertainty D = 0.7 0.1 < |y| < 0.7 Phys. Rev. Lett. 96, 122001 (2006) Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  13. kT Jets vs. D (0.1 < |y| < 0.7) D = 0.5 D = 1.0 Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  14. Forward Jets • Essentials to pin down PDFs vs. eventual New Physicsat higher Q2 in central region • DGLAP gives Q2 evolution • Expend x range toward low x High-x Low-x “Rutherford type” parton backscattering Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  15. kT Jets: Latest Results • D = 0.7 • 5 rapidity regions up to |y| = 2.1 • |y| < 0.1 • 0.1 < |y| < 0.7 • 0.7 < |y| < 1.1 • 1.1 < |y| < 1.6 • 1.6 < |y| < 2.1 •  L ~ 1 fb-1 Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  16. kT Jets with 1 fb-1: Data / Theory Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  17. Midpoint Jets with 1 fb-1: Data / Theory Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  18. Conclusion • Inclusive jet production measured with both kT and Midpoint • Both measurements based on ~ 1 fb-1 • 5 rapidity ranges, up to |y| = 2.1 • Careful treatment of non perturbative effects • Underlying Event well under control • Good agreement with NLO • Stringent test of pQCD over ~ 8 orders of magnitude • For central jets, pT reach extended by ~ 150 GeV/c with respect to Run I • To be used in future PDF global fits in orderto better constrain the gluon PDF at high x • Forward jets essentials Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  19. Backup Slides

  20. jet jet jet jet jet jet jet jet The kT Algorithm Step-by-Step Longitudinally invariant kT algorithm (Ellis-Soper inclusive mode) Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

  21. PERP axis PTJET1 PTPERP  PT//  // axis (bisector) PTJET2 Transverse Plan Bisector Method 0.1 < |y| < 0.7 • //  ISR • PERP  ISR  Detector Resolution • Assuming ISR democratic in  • D =  (2PERP - 2//) /  2  Detector Resolution Régis Lefèvre, QCD 06, July 3rd 2006, Montpellier, France

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