1. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 1 Toward an Understanding of Hadron-Hadron Collisions  Lecture 1: From Field-Feynman to the Tevatron.  Lecture 2: A Detailed Study of the “Underlying Event” at the Tevatron.  From 7 GeV/c  0 ’s to 600 GeV/c Jets!  QCD Monte-Carlo Models (PYTHIA Tune A).  “Min-Bias” Collisions at the Tevatron. → extrapolations to the LHC!  QCD Monte-Carlo Models tunes at the Tevatron. → extrapolations to the LHC! CMS at the LHC University of Perugia UE&MB@CMS Florida-Perugia

2. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 2 The Fermilab Tevatron  Fermi National Laboratory (Fermilab) is near Chicago, Illinois. CDF and DØ are the the two collider detector experiments at Fermilab.  Protons collide with antiprotons at a center-of- mass energy of almost 2 TeV (actually 1.96 TeV).

3. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 3 “Feynman-Field Jet Model” Feynman-Field Phenomenology  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). 1973-1980  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. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 7 Telagram from Feynman July 1976 SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE FEYNMAN

8. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 8 Letter from Feynman July 1976

9. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 9 Letter from Feynman: page 1 Spelling?

10. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 10 Letter from Feynman: page 3 It is fun! Onward!

11. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 11 Feynman Talk at Coral Gables in December 1976 “Feynman-Field Jet Model” 1 st transparency Last transparency

12. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 15 A Parameterization of the Properties of Jets 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. University of Perugia - Lecture 1 March 30, 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. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 17 Monte-Carlo Simulation of Hadron-Hadron Collisions  Color singlet proton collides with a color singlet antiproton.  A red quark gets knocked out of the proton and a blue antiquark gets knocked out of the antiproton.  At short times (small distances) the color forces are weak and the outgoing partons move away from the beam-beam remnants.  At long times (large distances) the color forces become strong and quark-antiquark pairs are pulled out of the vacuum and hadrons are formed.  The resulting event consists of hadrons and leptons in the form of two large transverse momentum outgoing jets plus the beam-beam remnants.

18. University of Perugia - Lecture 1 March 30, 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!

19. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 19 Collider Coordinates  The z-axis is defined to be the beam axis with the xy-plane being the “transverse” plane.   cm is the center-of-mass scattering angle and  is the azimuthal angle. The “transverse” momentum of a particle is given by P T = P cos(  cm ).  cm 090 o 140 o 215 o 36o6o 42o2o  Use  and  to determine the direction of an outgoing particle, where  is the “pseudo-rapidity” defined by  = -log(tan(  cm /2)).  The “rapidity” is defined by y = log((E+p z )/(E-p z ))/2 and is equal to  in the limit E >> mc 2.

20. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 20 Quark & Gluon Jets  The CDF calorimeter measures energy deposited in a cell of size  x  = 0.11x15 o, whch is converted into transverse energy, E T = E cos(  cm ).  “Jets” are defined to be clusters of transverse energy with a radius R in  -  space. A “jet” is the representation in the detector of an outgoing parton (quark or gluon).  The sum of the E T of the cells within a “jet” corresponds roughly to the E T of the outgoing parton and the position of the cluster in the grid gives the parton’s direction. Calorimeter Jets Can also construct jets from the charged particles!

21. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 21 CDF Run 2 DiJet Event July 2002 E T jet1 = 403 GeV E T jet2 = 322 GeV Raw E T values!!

22. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 22 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

23. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 23 Proton-AntiProton Collisions at the Tevatron  “Hard core” does not imply that a “hard” parton-parton collision has occured?  90% of “hard core” collisions are “soft hard core” and the proton and antiproton ooze through each other and fall apart (i.e. no hard scattering, P T (hard) < 5 GeV/c). The outgoing particles continue in roughly the same direction as initial proton and antiproton.  10% of the “hard core” collisions arise from a “hard” parton-parton collision (P T (hard) > 5 GeV/c) resulting in large transverse momentum outgoing partons.  About 0.3% of all parton-parton collisions produce a b-bbar quark pair (about 1/1,000 of all interactions).

24. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 24 CDF “Min-Bias” Data Charged Particle Density  Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity at 630 and 1,800 GeV. There are about 4.2 charged particles per unit  in “Min-Bias” collisions at 1.8 TeV (|  | < 1, all P T ). = 4.2 = 0.67  Convert to charged particle density, dN chg /d  d  by dividing by 2 . There are about 0.67 charged particles per unit  -  in “Min-Bias” collisions at 1.8 TeV (|  | < 1, all P T ).

25. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 25 1 charged particle dN chg /d  d  = 1/4  = 0.08 Particle Densities  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”

26. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 26 CDF “Min-Bias” Data Energy Dependence  Shows the center-of-mass energy dependence of the charged particle density, dN chg /d  d  for “Min-Bias” collisions at  = 0. Also show a log fit (Fit 1) and a (log) 2 fit (Fit 2) to the CDF plus UA5 data. = 0.51  = 0 630 GeV  What should we expect for the LHC? = 0.63  = 0 1.8 TeV LHC? 24% increase

27. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 27 Herwig “Soft” Min-Bias  Shows the center-of-mass energy dependence of the charged particle density, dN chg /d  d  for “Min-Bias” collisions compared with the HERWIG “Soft” Min-Bias Monte-Carlo model. Note: there is no “hard” scattering in HERWIG “Soft” Min-Bias.  HERWIG “Soft” Min-Bias contains no hard parton-parton interactions and describes fairly well the charged particle density, dN chg /d  d , in “Min-Bias” collisions.  HERWIG “Soft” Min-Bias predicts a 45% rise in dN chg /d  d  at  = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). 4 charged particles per unit  becomes 6. Can we believe HERWIG “soft” Min-Bias? Can we believe HERWIG “soft” Min-Bias? No! LHC?

28. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 28 CDF “Min-Bias” Data P T Dependence  Shows the P T dependence of the charged particle density, dN chg /d  d  dP T, for “Min-Bias” collisions at 1.8 TeV collisions compared with HERWIG “Soft” Min-Bias.  HERWIG “Soft” Min-Bias does not describe the “Min-Bias” data! The “Min-Bias” data contain a lot of “hard” parton-parton collisions which results in many more particles at large P T than are produces by any “soft” model.  Shows the energy dependence of the charged particle density, dN chg /d  d  for “Min-Bias” collisions compared with HERWIG “Soft” Min-Bias. Lots of “hard” scattering in “Min-Bias”!

29. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 29 Min-Bias: Combining “Hard” and “Soft” Collisions  HERWIG “hard” QCD with P T (hard) > 3 GeV/c describes well the high P T tail but produces too many charged particles overall. Not all of the “Min-Bias” collisions have a hard scattering with P T (hard) > 3 GeV/c!  One cannot run the HERWIG “hard” QCD Monte-Carlo with P T (hard) < 3 GeV/c because the perturbative 2-to-2 cross-sections diverge like 1/P T (hard) 4 ? HERWIG “soft” Min-Bias does not fit the “Min-Bias” data! No easy way to “mix” HERWIG “hard” with HERWIG “soft”.  HC HERWIG diverges! PYTHIA cuts off the divergence. Can run P T (hard)>0!

30. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 30 Monte-Carlo Simulation of Hadron-Hadron Collisions  The underlying event in a hard scattering process has a “hard” component (particles that arise from initial & final-state radiation and from the outgoing hard scattered partons) and a “soft?” component (“beam-beam remnants”).  Clearly? the “underlying event” in a hard scattering process should not look like a “Min- Bias” event because of the “hard” component (i.e. initial & final-state radiation).  However, perhaps “Min-Bias” collisions are a good model for the “beam-beam remnant” component of the “underlying event”. Are these the same?  The “beam-beam remnant” component is, however, color connected to the “hard” component so this comparison is (at best) an approximation. Maybe not all “soft”!

31. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 31 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).

32. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 32 PYTHIA 6.2: Multiple Parton Interaction Parameters Pythia uses multiple parton interactions to enhance the underlying event. ParameterValueDescription MSTP(81)0Multiple-Parton Scattering off 1Multiple-Parton Scattering on MSTP(82)1Multiple interactions assuming the same probability, with an abrupt cut-off P T min=PARP(81) 3Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a single Gaussian matter distribution, with a smooth turn- off P T0 =PARP(82) 4Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a double Gaussian matter distribution (governed by PARP(83) and PARP(84)), with a smooth turn-off P T0 =PARP(82) Hard Core Multiple parton interaction more likely in a hard (central) collision! and now HERWIG ! Jimmy: MPI J. M. Butterworth J. R. Forshaw M. H. Seymour Same parameter that cuts-off the hard 2-to-2 parton cross sections!

33. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 33 Tuning PYTHIA 6.2: Multiple Parton Interaction Parameters 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!

34. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 34 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) Tuned PYTHIA 6.206  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)). PYTHIA 6.206 CTEQ5L CDF Default! Run 1 Analysis

35. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 35 PYTHIA 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 “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”! PYTHIA Tune A CDF Run 2 Default

36. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 36 Min-Bias “Associated” Charged Particle Density  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!

37. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 37 Min-Bias “Associated” Charged Particle Density  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 Rapid rise in the particle density in the “transverse” region as PTmax increases!

38. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 38 Min-Bias “Associated” Charged PTsum Density  Use the maximum p T charged particle in the event, PTmax, to define a direction and look at the the “associated” PTsum density, dPT sum /d  d .  Shows the data on the  dependence of the “associated” charged PTsum density, dPT sum /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, dPT sum /d  d , for “min-bias” events. “Associated” densities do not include PTmax! Highest p T charged particle!

39. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 39 Min-Bias “Associated” Charged PTsum Density  Shows the data on the  dependence of the “associated” charged PTsum density, dPT sum /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 0.24 GeV/c per unit  -  Rapid rise in the PTsum density in the “transverse” region as PTmax increases!

40. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 40 Min-Bias “Associated” Charged Particle Density  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 GeV/c and PTmax > 2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).  PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e. Tune A “min-bias” is a bit too “jetty”). PTmax > 2.0 GeV/c PTmax > 0.5 GeV/c Transverse Region PY Tune A

41. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 41 Min-Bias “Associated” Charged PTsum Density  Shows the data on the  dependence of the “associated” charged PTsum density, dPT sum /d  d , for charged particles (p T > 0.5 GeV/c, |  | 0.5 GeV/c and PTmax > 2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).  PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e. Tune A “min-bias” is a bit too “jetty”). PTmax > 2.0 GeV/c PTmax > 0.5 GeV/c Transverse Region PY Tune A

42. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 42 PYTHIA Tune A LHC Predictions  PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV and 630 GeV.  Shows the center-of-mass energy dependence of the charged particle density, dN chg /d  d  for “Min-Bias” collisions compared with PYTHIA Tune A with P T (hard) > 0.  PYTHIA Tune A predicts a 42% rise in dN chg /d  d  at  = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). Similar to HERWIG “soft” min-bias, 4 charged particles per unit  becomes 6. LHC?

43. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 43 PYTHIA Tune A LHC Predictions  Shows the center-of-mass energy dependence of the charged particle density, dN chg /d  d  dP T, for “Min-Bias” collisions compared with PYTHIA Tune A with P T (hard) > 0.  PYTHIA Tune A predicts that 1% of all “Min-Bias” events at 1.8 TeV are a result of a hard 2-to-2 parton-parton scattering with P T (hard) > 10 GeV/c which increases to 12% at 14 TeV! 1% of “Min-Bias” events have P T (hard) > 10 GeV/c! 12% of “Min-Bias” events have P T (hard) > 10 GeV/c! LHC?

44. University of Perugia - Lecture 1 March 30, 2006 Rick Field – Florida/CDF/CMSPage 44 LHC Min-Bias Predictions Tevatron LHC  Both HERWIG and the tuned PYTHIA Tune A predict a 40-45% rise in dN chg /d  d  at  = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). 4 charged particles per unit  at the Tevatron becomes 6 per unit  at the LHC. 12 times more likely to find a 10 GeV “jet” in “Min-Bias” at the LHC!  The tuned PYTHIA Tune A predicts that 1% of all “Min-Bias” events at the Tevatron (1.8 TeV) are the result of a hard 2-to-2 parton-parton scattering with P T (hard) > 10 GeV/c which increases to 12% at LHC (14 TeV)!