Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 1 Toward an Understanding of the Overall Event Structure of Hard Collisions  The Past: Feynman-Field Fenomenology ( ).  The Present: Studying the “Underlying Event” at CDF. Outline of Talk 7 GeV  0 ’s to 400 GeV “jets”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 2 CDF Collider Phenomenology  I am a theorist working in the CDF experimental collaboration.  I work on collider phenomenology related to CDF.  Only by working in the experimental collaboration am I able to have access to data and do the kind of phenomenology I enjoy (i.e. the kind of phenomenology I did with Feynman many years ago). Theorist! In addition to being an exceptional theoretical physicist (and very good at math!), Feynman was a great phenomenologist and he enjoyed very much talking with experimenters.

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 3 “Feynman-Field Jet Model” Feynman-Field Fenomenology  FF1: “Quark Elastic Scattering as a Source of High Transverse Momentum Mesons”, R. D. Field and R. P. Feynman, Phys. Rev. D15, (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, (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, (1978)  FW1: “A QCD Model for e + e - Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, (1983). My 1 st graduate student!

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 4 “Feynman-Field Jet Model” Feynman-Field Fenomenology  FF1: “Quark Elastic Scattering as a Source of High Transverse Momentum Mesons”, R. D. Field and R. P. Feynman, Phys. Rev. D15, (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, (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, (1978)  FW1: “A QCD Model for e + e - Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, (1983). My 1 st graduate student! Many people have contributed to our understanding of hadron-hadron collisions! I will say a few words about Feynman’s influence on the field.

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 5 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! FF (preQCD) “Black-Box Model”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 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! FF (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 PT particles arise from direct hard collisions between constituent quarks in the incoming particles, which fragment or cascade down into several hadrons.” “Black-Box Model”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 7 Quark-Quark Black-Box Model FF (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 Festival August 23, 2002 Rick Field - Florida/CDFPage 8 Quark-Quark Black-Box Model FF (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.”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 9 Quark-Quark Black-Box Model FF (preQCD) Predict particle ratios Predict increase with increasing CM energy W Predict overall event topology (FFF1 paper 1977)

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 10 Telagram from Feynman July 1976 SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE FEYNMAN

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 11 Letter from Feynman July 1976

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 12 Letter from Feynman: page 1 Spelling?

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 13 Letter from Feynman: page 3 It is fun! Onward!

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 14 Napkin from Feynman

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 15 QCD Approach Quarks & Gluons FFF 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 Festival August 23, 2002 Rick Field - Florida/CDFPage 16 QCD Approach Quarks & Gluons FFF 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.”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 17 QCD Approach Quarks & Gluons FFF GeV! Predict large “jet” cross-section Feynman quote from FFF2: “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 PT discussed here.”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 18 CDF Run II DiJet Event July 2002 E T jet1 = 403 GeV E T jet2 = 322 GeV Raw E T values!!

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 19 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.

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 20 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

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 21 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 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,....”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 22 The “Underlying Event” in Hard Scattering Processes  What happens when a proton and an antiproton collide with a center-of- mass energy of 2 TeV?  Most of the time the proton and antiproton 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 “hard” parton-parton collision resulting in large transverse momentum outgoing partons.  The “underlying event” is everything except the two outgoing hard scattered “jets”. It is an unavoidable background to many collider observables.

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 23 Min-Bias? Beam-Beam Remnants  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).  However the “soft” component is color connected to the “hard” component so this separation is (at best) an approximation.  For ISAJET (no color flow) the “soft” and “hard” components are completely independent and the model for the beam-beam remnant component is the same as for min-bias (“cut pomeron”) but with a larger.  HERWIG breaks the color connection with a soft q-qbar pair and then models the beam-beam remnant component the same as HERWIG min-bias (cluster decay).

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 24 Studying the “Underlying Event” at CDF  The underlying event in a hard scattering process is a complicated and not very well understood object. It is an interesting region since it probes the interface between perturbative and non-perturbative physics.  There are two CDF analyses which quantitatively study the underlying event and compare with the QCD Monte-Carlo models.  It is important to model this region well since it is an unavoidable background to all collider observables. Also, we need a good model of min-bias (zero-bias) collisions. The Underlying Event: beam-beam remnants initial-state radiation multiple-parton interactions CDF Cone Analysis Valeria Tano Eve Kovacs Joey Huston Anwar Bhatti CDF Evolution of Charged Jets Rick Field David Stuart Rich Haas Ph.D. Thesis PRD65:092002, 2002

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 25 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

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 26 Charged Multiplicity versus P T (chgjet#1)  Data on the average number of “toward” (|  | 120 o ) charged particles (P T > 0.5 GeV, |  | in a 1 GeV bin. The solid (open) points are the Min-Bias (JET20) data. The errors on the (uncorrected) data include both statistical and correlated systematic uncertainties. Underlying Event “plateau” Factor of 2 more active than an average Min-Bias event!

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 27 ISAJET: “Transverse” Nchg versus P T (chgjet#1) ISAJET: “Transverse” Nchg versus P T (chgjet#1)  Plot shows the “transverse” vs P T (chgjet#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 Outgoing Jets plus Initial & Final-State Radiation

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 28 HERWIG: “Transverse” Nchg versus P T (chgjet#1)  Plot shows the “transverse” vs P T (chgjet#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 Outgoing Jets plus Initial & Final-State Radiation HERWIG

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 29 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).

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 30 PYTHIA: Multiple Parton Interactions Pythia uses multiple parton interactions to enhace 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 ! Herwig MPI J. M. Butterworth J. R. Forshaw M. H. Seymour

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 31 Parameter MSTP(81)1111 MSTP(82)1111 PARP(81) PARP(82) PARP(89)1,000 PARP(90)0.16 PARP(67) PYTHIA Defaults PYTHIA default parameters Constant Probability Scattering Default parameters give very poor description of the “underlying event”!  Plot shows “Transverse” versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA (P T (hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L.

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 32 ParameterTune 1Tune 2 MSTP(81)11 MSTP(82)33 PARP(82)1.6 GeV1.7 GeV PARP(85)1.0 PARP(86)1.0 PARP(89)1.8 TeV PARP(90)0.16 PARP(67) Old PYTHIA default (less initial-state radiation) New PYTHIA default (less initial-state radiation) Tuned PYTHIA Can we distinguish between PARP(67)=1 and PARP(67)=4?  Plot shows “Transverse” versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA (CTEQ5L, PARP(67)=1 and PARP(67)=4). PYTHIA CTEQ5L Old PYTHIA default (less initial-state radiation) New PYTHIA default (less initial-state radiation)

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 33 Collider Phenomenology From 7 GeV/c  o ’s to 400 GeV “Jets” FF1 (1977) 7 GeV/c  0 ’s NLO QCD (2002) 400 GeV “jets”

Feynman Festival August 23, 2002 Rick Field - Florida/CDFPage 34 Collider Phenomenology From 7 GeV/c  o ’s to 400 GeV “Jets” FF1 (1977) 7 GeV/c  0 ’s NLO QCD (2002) 400 GeV “jets” Rick Field (Feynman Festival): “At the time of this writing, there is still no sharp quantitative test of QCD. We believe it is the correct theory of strong interactions because it qualitatively describes an enormous variety and amount of data over many decades of Q 2.” Feynman played an enormous role in our understanding of hadron-hadron collisions and his influence is still being felt!