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Inclusive Jet Production using the k T Algorithm at CDF

HRPN-CT-2002-00292 E.U. Research Training Network Probe for New Physics. Inclusive Jet Production using the k T Algorithm at CDF. Régis Lefèvre Analysis done with Mario Martínez and Olga Norniella IFAE Barcelona. IMFP2006 XXXIV International Meeting on Fundamental Physics

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Inclusive Jet Production using the k T Algorithm at CDF

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  1. HRPN-CT-2002-00292 E.U. ResearchTraining Network Probe for New Physics Inclusive Jet Production using the kT Algorithm at CDF Régis Lefèvre Analysis done with Mario Martínez and Olga Norniella IFAE Barcelona IMFP2006 XXXIV International Meeting on Fundamental Physics April 2nd-7th 2006, Madrid, Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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 • New results based on 1 fb-1 Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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 order of magnitudes • 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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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 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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  12.  (hadron level with U.E.) CHAD =  (parton level no U.E.) Theoretical Predictions PDF uncertainty • NLO pQCD: JETRAD • Scale: R = F = max (PTJET) / 2 • PDFs: CTEQ6.1M package • Main uncertainty comes from PDFs • Gluon PDF at high x • CHAD = parton-to-hadron correction factor • Accounts for non perturbative contributions • Underlying Event (U.E.) • Hadronization • PYTHIA-Tune A used as nominal • HERWIG used for uncertainty D=0.7 and 0.1 < |y| < 0.7 CHAD Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  13. Published Results D = 0.7 0.1 < |y| < 0.7 Phys. Rev. Lett. 96 122001 (2006) Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  14. kT Jets vs. D (0.1 < |y| < 0.7) D = 0.5 D = 1.0 Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  15. 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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  16. New 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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  17. Data / Theory Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  18. Conclusion • Good agreement with NLO • 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 • Underlying Event well under control • To be used in future PDF global fits in orderto better constrain the gluon PDF at high x • Forward jets essentials • Prospect • cos * vs. dijet invariant mass • Limit on contact interactions Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  19. Backup Slides

  20. jet jet jet jet jet jet jet jet kT Algorithm Step-by-Step Longitudinally invariant kT algorithm (Ellis-Soper inclusive mode) Régis Lefèvre, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

  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, IMFP 2006, April 6th 2006, El Escorial, Madrid , Spain

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