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

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain2 Proton-antiproton collisions  s = 1.96 TeV 36 bunches: crossing time = 396 ns Peak luminosity ~ 1.2  cm -2 s -1 The Tevatron in Run II Collecting ~ 20 pb -1 / week About 1.6 fb -1 delivered

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain3 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 6 th 2006, El Escorial, Madrid, Spain4 Motivations Legacy from Run I –Great interest on apparent excess at high E T –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 ~ m PDFs at high Q 2 & high x Production enhanced at high p T thanks to new  s Run I CDF Inclusive Jet Data (Statistical Errors Only) JetClu R CONE = <|  |<0.7  R =  F =E T /2 R SEP =1.3 CTEQ4M PDFs CTEQ4HJ PDFs

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain5 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  R SEP to emulate experimental merging/splitting Arbitrary parameter R SEP : prescription R SEP = 1.3 (based on parton level approximate arguments) below threshold (no jets) above threshold (1 jet)

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain6 The k T Algorithm Inclusive k T algorithm –Merging pairs of nearby particles in order of increasing relative p T –D parameter controls merging termination and characterizes size of resulting jets p T classification inspired by pQCD gluon emissions –Infrared and Collinear safe to all orders in pQCD –No merging/splitting No R SEP 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)

Results from ZEUS / D0 Run I D0 Run I Disagreement at low p T  Suggests Underlying Event not properly accounted for

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain8 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 corrected for the Underlying Event and Hadronization Requires a Monte-Carlo generator able to reproduce the Underlying Event

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain9 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 6 th 2006, El Escorial, Madrid, Spain10 Energy Flow Inside Jets (1-  ) 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 (2005) 37 < p T < 380 GeV/c

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain11 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 p T 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 6 th 2006, El Escorial, Madrid, Spain12 Theoretical Predictions NLO pQCD: JETRAD –Scale:  R =  F = max (P T JET ) / 2 –PDFs: CTEQ6.1M package –Main uncertainty comes from PDFs Gluon PDF at high x C HAD = 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  (parton level no U.E.)  (hadron level with U.E.) C HAD = PDF uncertainty C HAD D=0.7 and 0.1 < |y| < 0.7

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain13 Published Results Phys. Rev. Lett (2006) D = < |y| < 0.7

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain14 k T Jets vs. D (0.1 < |y| < 0.7) D = 0.5 D = 1.0

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain15 Forward Jets Essentials to pin down PDFs vs. eventual New Physics at higher Q 2 in central region –DGLAP gives Q 2 evolution Expend x range toward low x High-xLow-x “Rutherford type” parton backscattering

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain16 New Results D = 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 6 th 2006, El Escorial, Madrid, Spain17 Data / Theory

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain18 Conclusion Good agreement with NLO –Stringent test of pQCD over ~ 8 orders of magnitude p T 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 order to better constrain the gluon PDF at high x –Forward jets essentials Prospect –cos  * vs. dijet invariant mass Limit on contact interactions

Backup Slides

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain20 k T Algorithm Step-by-Step jet Longitudinally invariant k T algorithm (Ellis-Soper inclusive mode)

Régis Lefèvre, IMFP 2006, April 6 th 2006, El Escorial, Madrid, Spain21  P T //  P T PERP PERP axis // axis (bisector) Transverse Plan P T JET2 P T JET1   Bisector Method  //  ISR  PERP  ISR  Detector Resolution Assuming ISR democratic in   D =  (  2 PERP -  2 // ) /  2  Detector Resolution 0.1 < |y| < 0.7