1. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 1 Fermilab Tevatron University Rick Field University of Florida CDF Run 2 Toward an Understanding of Hadron-Hadron Collisions From Feynman-Field to the Tevatron Fermilab 2006

2. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 2 Toward and Understanding of Hadron-Hadron Collisions  From 7 GeV/c  0 ’s to 600 GeV/c Jets.  Some things we have learned about quark and gluon jets at CDF.  Jet algorithms and the “jet” cross section at CDF. From Feynman-Field to the Tevatron FeynmanandField 1 st hat!

3. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 3 “Feynman-Field Jet Model” The Feynman-Field Days  FF1: “Quark Elastic Scattering as a Source of High Transverse Momentum Mesons”, R. D. Field and R. P. Feynman, Phys. Rev. D15, 2590-2616 (1977).  FFF1: “Correlations Among Particles and Jets Produced with Large Transverse Momenta”, R. P. Feynman, R. D. Field and G. C. Fox, Nucl. Phys. B128, 1-65 (1977).  FF2: “A Parameterization of the properties of Quark Jets”, R. D. Field and R. P. Feynman, Nucl. Phys. B136, 1-76 (1978).  F1: “Can Existing High Transverse Momentum Hadron Experiments be Interpreted by Contemporary Quantum Chromodynamics Ideas?”, R. D. Field, Phys. Rev. Letters 40, 997-1000 (1978).  FFF2: “A Quantum Chromodynamic Approach for the Large Transverse Momentum Production of Particles and Jets”, R. P. Feynman, R. D. Field and G. C. Fox, Phys. Rev. D18, 3320-3343 (1978). 1973-1983  FW1: “A QCD Model for e + e - Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, 65-84 (1983). My 1 st graduate student!

4. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 4 Hadron-Hadron Collisions  What happens when two hadrons collide at high energy?  Most of the time the hadrons ooze through each other and fall apart (i.e. no hard scattering). The outgoing particles continue in roughly the same direction as initial proton and antiproton.  Occasionally there will be a large transverse momentum meson. Question: Where did it come from?  We assumed it came from quark-quark elastic scattering, but we did not know how to calculate it! FF1 1977 (preQCD) Feynman quote from FF1 “The model we shall choose is not a popular one, so that we will not duplicate too much of the work of others who are similarly analyzing various models (e.g. constituent interchange model, multiperipheral models, etc.). We shall assume that the high P T particles arise from direct hard collisions between constituent quarks in the incoming particles, which fragment or cascade down into several hadrons.” “Black-Box Model”

5. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 5 Quark-Quark Black-Box Model FF1 1977 (preQCD) Quark Distribution Functions determined from deep-inelastic lepton-hadron collisions Quark Fragmentation Functions determined from e + e - annihilations Quark-Quark Cross-Section Unknown! Deteremined from hadron-hadron collisions. No gluons! Feynman quote from FF1 “Because of the incomplete knowledge of our functions some things can be predicted with more certainty than others. Those experimental results that are not well predicted can be “used up” to determine these functions in greater detail to permit better predictions of further experiments. Our papers will be a bit long because we wish to discuss this interplay in detail.”

6. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 6 Quark-Quark Black-Box Model FF1 1977 (preQCD) Predict particle ratios Predict increase with increasing CM energy W Predict overall event topology (FFF1 paper 1977) “Beam-Beam Remnants” 7 GeV/c  0 ’s!

7. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 7 Telagram from Feynman July 1976 SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE FEYNMAN

8. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 8 Letter from Feynman July 1976

9. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 9 Letter from Feynman Page 1 Spelling?

10. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 10 Letter from Feynman Page 3 It is fun! Onward!

11. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 11 Feynman Talk at Coral Gables (December 1976) “Feynman-Field Jet Model” 1 st transparency Last transparency

12. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 12 QCD Approach: Quarks & Gluons FFF2 1978 Parton Distribution Functions Q 2 dependence predicted from QCD Quark & Gluon Fragmentation Functions Q 2 dependence predicted from QCD Quark & Gluon Cross-Sections Calculated from QCD Feynman quote from FFF2 “We investigate whether the present experimental behavior of mesons with large transverse momentum in hadron-hadron collisions is consistent with the theory of quantum-chromodynamics (QCD) with asymptotic freedom, at least as the theory is now partially understood.”

13. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 13 High P T Jets 30 GeV/c! Predict large “jet” cross-section Feynman, Field, & Fox (1978) CDF (2006) 600 GeV/c Jets! Feynman quote from FFF “At the time of this writing, there is still no sharp quantitative test of QCD. An important test will come in connection with the phenomena of high P T discussed here.”

14. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 14 A Parameterization of the Properties of Jets  Assumed that jets could be analyzed on a “recursive” principle. Field-Feynman 1978 Original quark with flavor “a” and momentum P 0 bb pair (ba)  Let f(  )d  be the probability that the rank 1 meson leaves fractional momentum  to the remaining cascade, leaving quark “b” with momentum P 1 =  1 P 0. cc pair (cb)(cb) Primary Mesons  Assume that the mesons originating from quark “b” are distributed in presisely the same way as the mesons which came from quark a (i.e. same function f(  )), leaving quark “c” with momentum P 2 =  2 P 1 =  2  1 P 0.  Add in flavor dependence by letting  u = probabliity of producing u-ubar pair,  d = probability of producing d- dbar pair, etc.  Let F(z)dz be the probability of finding a meson (independent of rank) with fractional mementum z of the original quark “a” within the jet. Rank 2 continue Calculate F(z) from f(  ) and  i ! (bk)(bk)(ka) Rank 1 Secondary Mesons (after decay)

15. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 15 Feynman-Field Jet Model R. P. Feynman ISMD, Kaysersberg, France, June 12, 1977 Feynman quote from FF2 “The predictions of the model are reasonable enough physically that we expect it may be close enough to reality to be useful in designing future experiments and to serve as a reasonable approximation to compare to data. We do not think of the model as a sound physical theory,....”

16. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 16 Monte-Carlo Simulation of Hadron-Hadron Collisions FF1-FFF1 (1977) “Black-Box” Model F1-FFF2 (1978) QCD Approach FF2 (1978) Monte-Carlo simulation of “jets” FFFW “FieldJet” (1980) QCD “leading-log order” simulation of hadron-hadron collisions ISAJET (“FF” Fragmentation) HERWIG (“FW” Fragmentation) PYTHIA today “FF” or “FW” Fragmentation the past tomorrow SHERPAPYTHIA 6.3

17. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 17 QCD Monte-Carlo Models: High Transverse Momentum Jets  Start with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and final- state gluon radiation (in the leading log approximation or modified leading log approximation). “Hard Scattering” Component “Underlying Event”  The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or semi-soft multiple parton interactions (MPI).  Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” observables receive contributions from initial and final-state radiation. The “underlying event” is an unavoidable background to most collider observables and having good understand of it leads to more precise collider measurements!

18. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 18 Monte-Carlo Simulation of Quark and Gluon Jets  ISAJET: Evolve the parton-shower from Q 2 (virtual photon invariant mass) to Q min ~ 5 GeV. Use a complicated fragmentation model to evolve from Q min to outgoing hadrons. Q2Q2 Field-Feynman hadrons 5 GeV1 GeV 200 MeV  HERWIG: Evolve the parton-shower from Q 2 (virtual photon invariant mass) to Q min ~ 1 GeV. Form color singlet clusters which “decay” into hadrons according to 2-particle phase space.  MLLA: Evolve the parton-shower from Q 2 (virtual photon invariant mass) to Q min ~ 230 MeV. Assume that the charged particles behave the same as the partons with N chg /N parton = 0.56! CDF Distribution of Particles in Jets MLLA Curve! = ln(E jet /p particle )

19. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 19 Distribution of Particles in Jets  Ratio of charged hadron multiplicities in gluon and quark jets agrees with NNLLA  Gluon-Quark Ratio = 1.6  0.2  Momentum distribution of charged hadrons in jets well described by MLLA!  Dijet mass range 80-600 GeV  Cutoff Q eff = 230  40 MeV  N charged-hadrons /N partons = 0.56  0.10 CDF Run 1 Analysis Ratio = N g-jet / N q-jet Q = E jet   cone Both PYTHIA and HERWIG predict a Gluon-Quark Ratio that is smaller than the data!

20. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 20 Charged Multiplicity in Quark and Gluon Jets  CDF Run 1 data on the average charged particle multiplicities in gluon and quark jets versus Q = E jet ×  cone compared with NLLA, PYTHIA, and HERWIG.  HERWIG and PYTHIA correctly predict the charged multiplicity for gluon jets.  Both HERWIG and PYTHIA over-estimate the charged multiplicity in quark jets by ~30%! CDF Run 1 Analysis

21. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 21 Distribution of Particles in Quark and Gluon Jets  Momentum distribution of charged particles in gluon jets. HERWIG 5.6 predictions are in a good agreement with CDF data. PYTHIA 6.115 produces slightly more particles in the region around the peak of distribution. x = 0.37 0.14 0.05 0.02 0.007  Momentum distribution of charged particles in quark jets. Both HERWIG and PYTHIA produce more particles in the central region of distribution. p chg = 2 GeV/c Both PYTHIA and HERWIG predict more charged particles than the data for quark jets! CDF Run 1 Analysis

22. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 22 Evolution of Charged Jets “Underlying Event”  Look at charged particle correlations in the azimuthal angle  relative to the leading charged particle jet.  Define |  | 120 o as “Away”.  All three regions have the same size in  -  space,  x  = 2x120 o = 4  /3. Charged Particle  Correlations P T > 0.5 GeV/c |  | < 1 Look at the charged particle density in the “transverse” region! “Transverse” region very sensitive to the “underlying event”! CDF Run 1 Analysis

23. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 23 “Transverse” Charged Particle Density “Transverse” Charged Particle Density  Shows the data on the average “transverse” charge particle density (|  | 0.5 GeV) as a function of the transverse momentum of the leading charged particle jet from Run 1.  Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1. The errors on the (uncorrected) Run 2 data include both statistical and correlated systematic uncertainties. “Transverse” region as defined by the leading “charged particle jet” Excellent agreement between Run 1 and 2! PYTHIA Tune A was tuned to fit the “underlying event” in Run I!  Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after CDFSIM).

24. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 24 Charged Multiplicity in Charged Particle Jets  Plot shows the average number of charged particles (p T > 0.5 GeV, |  | < 1) within the leading charged particle jet (R = 0.7) as a function of the P T of the leading charged jet. The solid (open) points are Min-Bias (JET20) data. The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. The QCD “hard scattering” theory curves (Herwig 5.9, Isajet 7.32, Pythia 6.115) are corrected for the track finding efficiency. PYTHIA predict more charged particles than the data for charged jets! Includes charged particles from the “underlying event”! CDF Run 1 Analysis

25. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 25 Charged Multiplicity in Charged Particle Jets  CDF Run 1 data on the multiplicity distribution of charged particles (p T > 0.5 GeV and |  | 5 and 30 GeV compared with the QCD “hard scattering” Monte-Carlo predictions of HERWIG 5.9, ISAJET 7.32, and PYTHIA 6.115. Plot shows the percentage of events in which the leading charged jet (R = 0.7) contains N chg charged particles. CDF Run 1 Analysis Includes charged particles from the “underlying event”!

26. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 26 Radial Charged Distribution in Charged Particle Jets  Charged multiplicity flow in the radial distance R in  -  space from chgjet#1 (leading charged jet) for charged particles with p T > 0.5 GeV and |  | 5 and 30 GeV. The points are in a 0.02 bin of R.  Charged PTsum flow in the radial distance R in  -  space from chgjet#1 (leading charged jet) for charged particles with p T > 0.5 GeV and |  | 5 and 30 GeV. The points are the scalar in a 0.02 bin of R.

27. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 27 Run 1 Fragmentation Function  CDF Run 1 data on the momentum distribution of charged particles (p T > 0.5 GeV and |  | < 1) within chgjet#1 (leading charged jet). The points are the charged number density, F(z) = dN chg /dz, where z = p chg /P(chgjet#1) is the ratio of the charged particle momentum to the charged momentum of chgjet#1. The integral of F(z) is the average number of particles within chgjet#1. Includes charged particles from the “underlying event”! CDF Run 1 Analysis

28. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 28 Run 1 Fragmentation Function  CDF Run 1 data from on the momentum distribution of charged particles (p T > 0.5 GeV and |  | 5 GeV compared with the QCD “hard scattering” Monte-Carlo predictions of HERWIG, ISAJET, and PYTHIA. The points are the charged number density, F(z) = dN chg /dz, where z = p chg /P(chgjet#1) is the ratio of the charged particle momentum to the charged momentum of chgjet#1. CDF Run 1 Analysis PYTHIA does not agree at high z!

29. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 29 Run 1 Fragmentation Function  Data from Fig. 3.8 on the momentum distribution of charged particles (p T > 0.5 GeV and |  | 30 GeV compared with the QCD “hard scattering” Monte-Carlo predictions of HERWIG, ISAJET, and PYTHIA. The points are the charged number density, F(z) =dNchg/dz, where z = p chg /P(chgjet#1) is the ratio of the charged particle momentum to the charged momentum of chgjet#1. CDF Run 1 Analysis PYTHIA does not agree at high z!

30. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 30 The “Transverse” Regions as defined by the Leading Jet  Look at charged particle correlations in the azimuthal angle  relative to the leading calorimeter jet (JetClu R = 0.7, |  | < 2).  Define |  | 120 o as “Away”. Each of the two “transverse” regions have area  = 2x60 o = 4  /6. The overall “transverse” region is the sum of the two transverse regions (  = 2x120 o = 4  /3). Charged Particle  Correlations p T > 0.5 GeV/c |  | < 1 “Transverse” region is very sensitive to the “underlying event”! Look at the charged particle density in the “transverse” region! CDF Run 2 Analysis

31. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 31 Charged Particle Density  Dependence  Look at the “transverse” region as defined by the leading jet (JetClu R = 0.7, |  | 150 o ) with almost equal transverse energies (E T (jet#2)/E T (jet#1) > 0.8) and with E T (jet#3) < 15 GeV.  Shows the  dependence of the charged particle density, dN chg /d  d , for charged particles in the range p T > 0.5 GeV/c and |  | < 1 relative to jet#1 (rotated to 270 o ) for 30 < E T (jet#1) < 70 GeV for “Leading Jet” and “Back-to-Back” events. Refer to this as a “Leading Jet” event Refer to this as a “Back-to-Back” event Subset

32. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 32 “Transverse” Charge Density PYTHIA Tune A vs HERWIG  Shows the average charged particle density, dN chg /d  d , in the “transverse” region (p T > 0.5 GeV/c, |  | < 1) versus E T (jet#1) for “Leading Jet” and “Back-to-Back” events. “Leading Jet” “Back-to-Back” Now look in detail at “back-to-back” events in the region 30 < E T (jet#1) < 70 GeV!  Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM.

33. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 33 Charged Particle Density PYTHIA Tune A vs HERWIG HERWIG (without multiple parton interactions) produces too few charged particles in the “transverse” region for 30 < E T (jet#1) < 70 GeV! PYTHIA produces too many particle in the “away-side” jet!

34. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 34 “Transverse” PTsum Density PYTHIA Tune A vs HERWIG  Shows the average charged PTsum density, dPT sum /d  d , in the “transverse” region (p T > 0.5 GeV/c, |  | < 1) versus E T (jet#1) for “Leading Jet” and “Back-to-Back” events.  Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM. “Leading Jet” “Back-to-Back” Now look in detail at “back-to-back” events in the region 30 < E T (jet#1) < 70 GeV!

35. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 35 Charged PTsum Density PYTHIA Tune A vs HERWIG HERWIG (without multiple parton interactions) does not produces enough PTsum in the “transverse” region for 30 < E T (jet#1) < 70 GeV! PYTHIA produces too many particle in the “away-side” jet!

36. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 36 Jet Algorithms  Clustering algorithms are used to combine calorimeter towers or charged particles into “jets” in order to study the event topology and to compare with the QCD Monte-Carlo Models.  We do not detect partons! The outgoing partons fragment into hadrons before they travel a distance of about the size of the proton. At long distances the partons manifest themselves as “jets”. The “underlying event” can also form “jets”. Most “jets” are a mixture of particles arising from the “hard” outgoing partons and the “underlying event”.  Every “jet” algorithms correspond to a different observable and different algorithms give different results.  Since we measure hadrons every observable is infrared and collinear safe. There are no divergences at the hadron level!  Studying the difference between the algorithms teaches us about the event structure.

37. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 37 Jet Corrections & Extrapolations  Calorimeter Level Jets → Hadron Level Jets:  We measure “jets” at the “hadron level” in the calorimeter.  We certainly want to correct the “jets” for the detector resolution and efficiency.  Also, we must correct the “jets” for “pile-up”.  Must correct what we measure back to the true “hadron level” (i.e. particle level) observable!  Particle Level Jets (with the “underlying event” removed):  Do we want to make further model dependent corrections?  Do we want to try and subtract the “underlying event” from the observed “particle level” jets.  This cannot really be done, but if you trust the Monte-Carlo modeling of the “underlying event” you can do it by using the Monte-Carlo models (use PYTHIA Tune A).  This is no longer an observable, it is a model dependent extrapolation!  Hadron Level Jets → Parton Level Jets:  Do we want to use the data to try and extrapolate back to the parton level? What parton level, PYTHIA (Leading Log) or fixed order NLO?  This also cannot really be done, but again if you trust the Monte- Carlo models you can try and do it by using the Monte-Carlo models (use PYTHIA Tune A) including ISR and FSR.  Cannot extrapolate the data to fixed order NLO! I do not believe we should extrapolate the data to the parton level! We should publish what we measure (i.e. hadron level with the “underlying event”)! To compare with theory we should “extrapolate” the parton level to the hadron level (i.e. add hadronization and the “underlying event” to the parton level)! PYTHIA, HERWIG, MC@NLO Hadron ← Parton Useless without a model of hadronization! Next-to-leading order parton level calculation 0, 1, 2, or 3 partons!

38. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 38 Good and Bad Algorithms  In order to correct what we see in the calorimeter back to the hadron level we must use an algorithm that can be defined at both the calorimeter and particle level.  If you insist on extrapolating the data to the parton level then it is better to use an algorithm that is well defined at the parton level (i.e. infrared and collinear safe at the parton level). Infrared Safety (Parton Level) Soft parton emission changes jet multiplicity below threshold (no jets) above threshold (1 jet) Collinear Safety (Parton Level)  If you hadronize the parton level and add the “underlying event” (i.e. PYTHIA, HERWIG, MC@NLO) then you do not care if the algorithm is infrared and collinear safe at the parton level. You can predict any hadron level observable!

39. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 39 Four Jet Algorithms  JetClu is bad because the algorithm cannot be defined at the particle level. Bad  The MidPoint and Modified MidPoint (i.e. Search Cone) algorithms are not infrared and collinear safe at the parton level. Towers not included in a jet (i.e. “dark towers”)!

40. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 40 K T Algorithm  kT Algorithm:  Cluster together calorimeter towers by their kT proximity.  Infrared and collinear safe at all orders of pQCD.  No splitting and merging.  No ad hoc Rsep parameter necessary to compare with parton level.  Every parton, particle, or tower is assigned to a “jet”.  No biases from seed towers.  Favored algorithm in e+e- annihilations! K T Algorithm Only towers with E T > 0.5 GeV are shown Raw Jet E T = 533 GeV Raw Jet E T = 618 GeV Will the K T algorithm be effective in the collider environment where there is an “underlying event”? CDF Run 2

41. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 41 K T Inclusive Jet Cross Section  K T Algorithm (D = 0.7)  Data corrected to the hadron level  L = 385 pb -1  0.1 < |y jet | < 0.7  Compared with NLO QCD (JetRad) corrected to the hadron level. Sensitive to UE + hadronization effects for P T < 300 GeV/c!

42. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 42 Search Cone Inclusive Jet Cross Section  Modified MidPoint Cone Algorithm (R = 0.7, f merge = 0.75)  Data corrected to the hadron level and the parton level  L = 1.04 fb -1  0.1 < |y jet | < 0.7  Compared with NLO QCD (JetRad, R sep = 1.3) Sensitive to UE + hadronization effects for P T < 200 GeV/c!

43. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 43 Hadronization and “Underlying Event” Corrections  Compare the hadronization and “underlying event” corrections for the K T algorithm (D = 0.7) and the MidPoint algorithm (R = 0.7)! MidPoint Cone Algorithm (R = 0.7) The K T algorithm is slightly more sensitive to the “underlying event”!  We see that the K T algorithm (D = 0.7) is slightly more sensitive to the underlying event than the cone algorithm (R = 0.7), but with a good model of the “underlying event” both cross sections can be measured at the Tevatrun! Note that DØ does not make any corrections for hadronization or the “underlying event”!?

44. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 44 Summary and Conclusions  Neither HERWIG or PYTHIA describe perfectly the distribution charged particles in quark and gluon jets at the Tevatron!  To learn about the fragmentation function at large z we should compare the inclusive “jet” cross-section to the inclusive charged particle cross section!  We have events with 600 GeV “jets” so we must have events with 300 GeV/c charged particles! Was this measured in Run 1?  A lot of work has been done in comparing to analytic MLLA calculations (Korytov and students), but more work needs to be done in improving the fragmentation models in HERWIG and PYTHIA!  I wish I could show you the following:  CDF measured fragmentation functions at different Q 2 compared with PYTHIA and HERWIG.  The k T distribution of charged particles within “jets” compared with PYTHIA and HERWIG.  The ratio of the inclusive charged particle cross-section to the inclusive “jet” cross-section compared with PYTHIA and HERWIG. In 1 fb -1 we have thousands of charged tracks with p T > 100 GeV/c! Charged Particle k T Distribution in Jets Shape Comparison Only Sergo’s latest “blessing” from the CDF-QCD group!

45. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 45 Inclusive & Exclusive 3-Jet Study CDF Run 2 CDF analysis using 1fb -1. At least 1 Jet (“trigger” jet) (P T > PT trig, |  | < 1.0) Exactly 3 jets (Exclusive) (P T > PT min, |  | < 2.5) More than 2 jets (Inclusive) (P T > PT min, |  | < 2.5) ProtonAnti-proton Order Jets by P T Jet1 highest P T, etc. Jet1 Jet2 Jet3 Jet4 MidPoint R = 0.4 and JetClu R = 0.4 Charged Particle Jets RDF Algorithm R = 0.4

46. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 46 MIT Search Scheme 12 Exclusive 3 Jet Final State Challenge Bruce KnutesonMarkus Klute Khaldoun Makhoul Georgios Choudalakis Ray Culbertson Conor Henderson Gene Flanagan Exactly 3 jets (P T > 20 GeV/c, |  | < 2.5) At least 1 Jet (“trigger” jet) (P T > 40 GeV/c, |  | < 1.0) CDF Data (MIT JetClu R=0.4) PYTHIA Tune A Normalized to 1 Order Jets by P T Jet1 highest P T, etc. R(j2,j3)

47. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 47 Exc3J R(j2,j3) Normalized  Let Ntrig40 equal the number of events with at least one jet with P T > 40 GeV/c and |  | < 1.0 (this is the “offline” trigger).  Let N3Jexc20 equal the number of events with exactly three jets with P T > 20 GeV/c and |  | 40 GeV/c and |  | < 1.0.  Let N3JexcFr = N3Jexc20/Ntrig40. The is the fraction of the “offline” trigger events that are exclusive 3-jet events.  The CDF data (MIT JetClu R=0.4) on dN/dR(j2,j3) at 1.96 TeV compared with PYTHIA Tune AW (PARP(67)=4), Tune DW (PARP(67)=2.5), Tune BW (PARP(67)=1).  PARP(67) affects the initial-state radiation which contributes primarily to the region R(j2,j3) > 1.0. Normalized to N3JexcFr R > 1.0 The data have more 3 jet events with small R(j2,j3)!? CDF Data (MIT JetClu R=0.4) data corrected using “jet corrections”!

48. Fermilab Tevatron University December 14, 2006 Rick Field – Florida/CDF/CMSPage 48 Exc3J R(j2,j3) Normalized  Let Ntrig40 equal the number of events with at least one jet with P T > 40 GeV/c and |  | < 1.0 (this is the “offline” trigger).  Let N3Jexc20 equal the number of events with exactly three jets with P T > 20 GeV/c and |  | 40 GeV/c and |  | < 1.0.  Let N3JexcFr = N3Jexc20/Ntrig40. The is the fraction of the “offline” trigger events that are exclusive 3-jet events.  The CDF data (MIT JetClu R=0.4) on dN/dR(j2,j3) at 1.96 TeV compared with PYTHIA Tune DW (PARP(67)=2.5) and HERWIG (without MPI).  Final-State radiation contributes to the region R(j2,j3) < 1.0. Normalized to N3JexcFr  If you ignore the normalization and normalize all the distributions to one then the data prefer Tune BW, but I believe this is misleading. R < 1.0 UF-MIT (and Steve Mrenna) are working to understand the CDF inclusive and exclusive 3-jet data!