1. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 1 Toward an Understanding of Hadron-Hadron Collisions Rick Field University of Florida Outline of Talk LBNL January 15, 2009 CMS at the LHC CDF Run 2  The early days of Feynman-Field Phenomenology.  Studying “min-bias” collisions and the “underlying event” at CDF.  Extrapolations to the LHC. From Feynman-Field to the LHC  Before Feynman-Field Phenomenology.

2. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 2 Before Feynman-Field Rick Field 1964 R. D. Field University of California, Berkeley, 1962-66 (undergraduate) University of California, Berkeley, 1966-71 (graduate student) me My sister Sally! The very first “Berkeley Physics Course”! My Ph.D. advisor! J.D.J Bob Cahn Chris Quigg me

3. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 3 Before Feynman-Field Rick & Jimmie 1968 Rick & Jimmie 1970 Rick & Jimmie 1972 (pregnant!) Rick & Jimmie at CALTECH 1973

4. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 4 Toward and Understanding of Hadron-Hadron Collisions  From 7 GeV/c  0 ’s to 600 GeV/c Jets. The early days of trying to understand and simulate hadron- hadron collisions. Feynman-Field Phenomenology FeynmanandField 1 st hat!

5. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 5 “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!

6. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 6 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”

7. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 7 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.”

8. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 8 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!

9. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 9 Telagram from Feynman July 1976 SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE FEYNMAN

10. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 10 Letter from Feynman July 1976

11. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 11 Letter from Feynman Page 1 Spelling?

12. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 12 Letter from Feynman Page 3 It is fun! Onward!

13. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 13 Feynman Talk at Coral Gables (December 1976) “Feynman-Field Jet Model” 1 st transparency Last transparency

14. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 14 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.”

15. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 15 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)

16. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 16 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,....”

17. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 17 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 6.4

18. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 18 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.”

19. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 19 CDF DiJet Event: M(jj) ≈ 1.4 TeV E T jet1 = 666 GeV E T jet2 = 633 GeV E sum = 1,299 GeV M(jj) = 1,364 GeV M(jj)/E cm ≈ 70%!!

20. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 20 The Fermilab Tevatron  I joined CDF in January 1998. CDF “SciCo” Shift December 12-19, 2008 Acquired 4728 nb -1 during 8 hour “owl” shift! My wife Jimmie on shift with me!

21. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 21 Proton-AntiProton Collisions at the Tevatron  tot =  EL  SD   DD   HC 1.8 TeV: 78mb = 18mb + 9mb + (4-7)mb + (47-44)mb The CDF “Min-Bias” trigger picks up most of the “hard core” cross-section plus a small amount of single & double diffraction. The “hard core” component contains both “hard” and “soft” collisions. Beam-Beam Counters 3.2 < |  | < 5.9 CDF “Min-Bias” trigger 1 charged particle in forward BBC AND 1 charged particle in backward BBC  tot =  EL  IN

22. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 22 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!

23. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 23 1 charged particle dN chg /d  d  = 1/4  = 0.08  Study the charged particles (p T > 0.5 GeV/c, |  | < 1) and form the charged particle density, dN chg /d  d , and the charged scalar p T sum density, dPT sum /d  d . Charged Particles p T > 0.5 GeV/c |  | < 1  = 4  = 12.6 1 GeV/c PTsum dPT sum /d  d  = 1/4  GeV/c = 0.08 GeV/cdN chg /d  d  = 3/4  = 0.24 3 charged particles dPT sum /d  d  = 3/4  GeV/c = 0.24 GeV/c 3 GeV/c PTsum CDF Run 2 “Min-Bias” Observable Average Average Density per unit  -  N chg Number of Charged Particles (p T > 0.5 GeV/c, |  | < 1) 3.17 +/- 0.310.252 +/- 0.025 PT sum (GeV/c) Scalar p T sum of Charged Particles (p T > 0.5 GeV/c, |  | < 1) 2.97 +/- 0.230.236 +/- 0.018 Divide by 4  CDF Run 2 “Min-Bias” Particle Densities

24. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 24  Use the maximum p T charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dN chg /d  d , in “min-bias” collisions (p T > 0.5 GeV/c, |  | < 1). “Associated” densities do not include PTmax! Highest p T charged particle!  Shows the data on the  dependence of the “associated” charged particle density, dN chg /d  d , for charged particles (p T > 0.5 GeV/c, |  | < 1, not including PTmax) relative to PTmax (rotated to 180 o ) for “min-bias” events. Also shown is the average charged particle density, dN chg /d  d , for “min-bias” events. It is more probable to find a particle accompanying PTmax than it is to find a particle in the central region! CDF Run 1 Min-Bias “Associated” Charged Particle Density

25. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 25  Shows the data on the  dependence of the “associated” charged particle density, dN chg /d  d , for charged particles (p T > 0.5 GeV/c, |  | 0.5, 1.0, and 2.0 GeV/c. Transverse Region  Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!). Ave Min-Bias 0.25 per unit  -  PTmax > 0.5 GeV/c PTmax > 2.0 GeV/c CDF Run 1 Min-Bias “Associated” Charged Particle Density Rapid rise in the particle density in the “transverse” region as PTmax increases!

26. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 26  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 CDF Run 1: Evolution of Charged Jets “Underlying Event”

27. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 27  Compares the average “transverse” charge particle density with the average “Min-Bias” charge particle density (|  | 0.5 GeV). Shows how the “transverse” charge particle density and the Min-Bias charge particle density is distributed in p T. CDF Run 1 Min-Bias data = 0.25 P T (charged jet#1) > 30 GeV/c “Transverse” = 0.56 Factor of 2! “Min-Bias” Run 1 Charged Particle Density “Transverse” p T Distribution

28. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 28  Plot shows average “transverse” charge particle density (|  | 0.5 GeV) versus P T (charged jet#1) compared to the QCD hard scattering predictions of ISAJET 7.32 (default parameters with P T (hard)>3 GeV/c).  The predictions of ISAJET are divided into two categories: charged particles that arise from the break-up of the beam and target (beam-beam remnants); and charged particles that arise from the outgoing jet plus initial and final-state radiation (hard scattering component). Beam-Beam Remnants ISAJET “Hard” Component ISAJET 7.32 “Transverse” Density ISAJET uses a naïve leading-log parton shower-model which does not agree with the data!

29. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 29  Plot shows average “transverse” charge particle density (|  | 0.5 GeV) versus P T (charged jet#1) compared to the QCD hard scattering predictions of HERWIG 5.9 (default parameters with P T (hard)>3 GeV/c).  The predictions of HERWIG are divided into two categories: charged particles that arise from the break-up of the beam and target (beam-beam remnants); and charged particles that arise from the outgoing jet plus initial and final-state radiation (hard scattering component). Beam-Beam Remnants HERWIG “Hard” Component HERWIG uses a modified leading- log parton shower-model which does agrees better with the data! HERWIG 6.4 “Transverse” Density

30. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 30 MPI: Multiple Parton Interactions  PYTHIA models the “soft” component of the underlying event with color string fragmentation, but in addition includes a contribution arising from multiple parton interactions (MPI) in which one interaction is hard and the other is “semi-hard”.  The probability that a hard scattering events also contains a semi-hard multiple parton interaction can be varied but adjusting the cut-off for the MPI.  One can also adjust whether the probability of a MPI depends on the P T of the hard scattering, P T (hard) (constant cross section or varying with impact parameter).  One can adjust the color connections and flavor of the MPI (singlet or nearest neighbor, q-qbar or glue-glue).  Also, one can adjust how the probability of a MPI depends on P T (hard) (single or double Gaussian matter distribution).

31. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 31 ParameterDefaultDescription PARP(83)0.5Double-Gaussian: Fraction of total hadronic matter within PARP(84) PARP(84)0.2Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the total hadronic matter. PARP(85)0.33Probability that the MPI produces two gluons with color connections to the “nearest neighbors. PARP(86)0.66Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs. PARP(89)1 TeVDetermines the reference energy E 0. PARP(90)0.16Determines the energy dependence of the cut-off P T0 as follows P T0 (E cm ) = P T0 (E cm /E 0 )  with  = PARP(90) PARP(67)1.0A scale factor that determines the maximum parton virtuality for space-like showers. The larger the value of PARP(67) the more initial- state radiation. Hard Core Take E 0 = 1.8 TeV Reference point at 1.8 TeV Determine by comparing with 630 GeV data! Affects the amount of initial-state radiation! Tuning PYTHIA: Multiple Parton Interaction Parameters

32. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 32 Default parameters give very poor description of the “underlying event”! Note Change PARP(67) = 4.0 (< 6.138) PARP(67) = 1.0 (> 6.138) Parameter6.1156.1256.1586.206 MSTP(81)1111 MSTP(82)1111 PARP(81)1.41.9 PARP(82)1.552.1 1.9 PARP(89)1,000 PARP(90)0.16 PARP(67)4.0 1.0  Plot shows the “Transverse” charged particle density versus P T (chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (P T (hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L. PYTHIA default parameters PYTHIA 6.206 Defaults MPI constant probability scattering

33. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 33 Old PYTHIA default (more initial-state radiation) New PYTHIA default (less initial-state radiation) ParameterTune BTune A MSTP(81)11 MSTP(82)44 PARP(82)1.9 GeV2.0 GeV PARP(83)0.5 PARP(84)0.4 PARP(85)1.00.9 PARP(86)1.00.95 PARP(89)1.8 TeV PARP(90)0.25 PARP(67)1.04.0 Old PYTHIA default (more initial-state radiation) New PYTHIA default (less initial-state radiation)  Plot shows the “transverse” charged particle density versus P T (chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set B (PARP(67)=1) and Set A (PARP(67)=4)). Run 1 Analysis Run 1 PYTHIA Tune A PYTHIA 6.206 CTEQ5L CDF Default!

34. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 34  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. 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). Run 1 vs Run 2: “Transverse” Charged Particle Density “Transverse” region as defined by the leading “charged particle jet”

35. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 35 PYTHIA Tune A Min-Bias “Soft” + ”Hard”  PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with P T (hard) > 0. One can simulate both “hard” and “soft” collisions in one program.  The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned. Tuned to fit the CDF Run 1 “underlying event”! 12% of “Min-Bias” events have P T (hard) > 5 GeV/c! 1% of “Min-Bias” events have P T (hard) > 10 GeV/c!  This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2 parton-parton scattering with P T (hard) > 5 GeV/c (1% with P T (hard) > 10 GeV/c)! Lots of “hard” scattering in “Min-Bias” at the Tevatron! PYTHIA Tune A CDF Run 2 Default Tune A Tune AW Tune B Tune BW Tune D Tune DW Tune D6 Tune D6T These are “old” PYTHIA 6.2 tunes! There are new 6.4 tunes by Arthur Moraes (ATLAS) Hendrik Hoeth (MCnet) Peter Skands (Tune S0)

36. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 36 Min-Bias Correlations  Data at 1.96 TeV on the average p T of charged particles versus the number of charged particles (p T > 0.4 GeV/c, |  | < 1) for “min-bias” collisions at CDF Run 2. The data are corrected to the particle level and are compared with PYTHIA Tune A at the particle level (i.e. generator level).

37. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 37 Min-Bias: Average PT versus Nchg =+ +  Beam-beam remnants (i.e. soft hard core) produces low multiplicity and small with independent of the multiplicity.  Hard scattering (with no MPI) produces large multiplicity and large.  Hard scattering (with MPI) produces large multiplicity and medium. The CDF “min-bias” trigger picks up most of the “hard core” component! This observable is sensitive to the MPI tuning!

38. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 38 Average PT versus Nchg  Data at 1.96 TeV on the average p T of charged particles versus the number of charged particles (p T > 0.4 GeV/c, |  | < 1) for “min-bias” collisions at CDF Run 2. The data are corrected to the particle leveland are compared with PYTHIA Tune A, Tune DW, and the ATLAS tune at the particle level (i.e. generator level).  Particle level predictions for the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.

39. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 39 Average PT versus Nchg =+  Z-boson production (with low p T (Z) and no MPI) produces low multiplicity and small. +  High p T Z-boson production produces large multiplicity and high.  Z-boson production (with MPI) produces large multiplicity and medium. No MPI!

40. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 40 Average PT(Z) versus Nchg  Data on the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (i.e. generator level). No MPI!  Predictions for the average P T (Z-Boson) versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2.

41. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 41 Average PT versus Nchg  Predictions for the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, P T (pair) < 10 GeV/c) at CDF Run 2.  Data the average p T of charged particles versus the number of charged particles (p T > 0.5 GeV/c, |  | < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, P T (pair) < 10 GeV/c) at CDF Run 2. The data are corrected to the particle level and are compared with various Monte-Carlo tunes at the particle level (i.e. generator level). P T (Z) < 10 GeV/c No MPI! Remarkably similar behavior! Perhaps indicating that MPI playing an important role in both processes.

42. Lawrence Berkeley Laboratory January 15, 2009 Rick Field – Florida/CDF/CMSPage 42 UE&MB@CMS  “Underlying Event” Studies: The “transverse region” in “leading Jet” and “back-to-back” charged particle jet production and the “central region” in Drell-Yan production. (requires charged tracks and muons for Drell- Yan)  Drell-Yan Studies: Transverse momentum distribution of the lepton-pair versus the mass of the lepton-pair,,, d  /dp T (pair) (only requires muons). Event structure for large lepton-pair p T (i.e.  +jets, requires muons).  Min-Bias Studies: Charged particle distributions and correlations. Construct “charged particle jets” and look at “mini-jet” structure and the onset of the “underlying event”. (requires only charged tracks) UE&MB@CMS Study the “underlying event” by using charged particles and muons! (start as soon as possible) is much larger at the LHC! Shapes of the p T (  +  - ) distribution at the Z-boson mass. DWT