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Toward an Understanding of the Overall Event Structure of Hard Collisions

Toward an Understanding of the Overall Event Structure of Hard Collisions. The Past: Feynman-Field Fenomenology (1973-1980). Outline of Talk. 7 GeV p 0 ’s to 400 GeV “jets”. The Present: Studying the “Underlying Event” at CDF. CDF Collider Phenomenology.

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Toward an Understanding of the Overall Event Structure of Hard Collisions

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  1. Toward an Understanding ofthe Overall Event Structureof Hard Collisions • The Past: Feynman-Field Fenomenology (1973-1980). Outline of Talk 7 GeV p0’s to 400 GeV “jets” • The Present: Studying the “Underlying Event” at CDF. Rick Field - Florida/CDF

  2. CDF ColliderPhenomenology • I am a theorist working in the CDF experimental collaboration. 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. Theorist! • 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). Rick Field - Florida/CDF

  3. Feynman-FieldFenomenology 1973-1980 “Feynman-Field Jet Model” • 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). • FW1: “A QCD Model for e+e- Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, 65-84 (1983). My 1st graduate student! Rick Field - Florida/CDF

  4. Feynman-FieldFenomenology 1973-1980 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-Field Jet Model” • 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). • FW1: “A QCD Model for e+e- Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, 65-84 (1983). My 1st graduate student! Rick Field - Florida/CDF

  5. Hadron-Hadron Collisions FF1 1977 (preQCD) • 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! “Black-Box Model” Rick Field - Florida/CDF

  6. Hadron-Hadron Collisions FF1 1977 (preQCD) • What happens when two hadrons collide at high energy? 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.” • 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! “Black-Box Model” Rick Field - Florida/CDF

  7. Quark-QuarkBlack-Box Model No gluons! 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. Rick Field - Florida/CDF

  8. Quark-QuarkBlack-Box Model No gluons! FF1 1977 (preQCD) Quark Distribution Functions determined from deep-inelastic lepton-hadron collisions 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.” Quark Fragmentation Functions determined from e+e- annihilations Quark-Quark Cross-Section Unknown! Deteremined from hadron-hadron collisions. Rick Field - Florida/CDF

  9. Quark-QuarkBlack-Box Model Predict particle ratios FF1 1977 (preQCD) Predict increase with increasing CM energy W Predict overall event topology (FFF1 paper 1977) Rick Field - Florida/CDF

  10. Telagram from Feynman July 1976 SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITE FEYNMAN Rick Field - Florida/CDF

  11. Letter from Feynman July 1976 Rick Field - Florida/CDF

  12. Letter from Feynman:page 1 Spelling? Rick Field - Florida/CDF

  13. Letter from Feynman:page 3 It is fun! Onward! Rick Field - Florida/CDF

  14. Napkin from Feynman Rick Field - Florida/CDF

  15. QCD ApproachQuarks & Gluons Quark & Gluon Fragmentation Functions Q2 dependence predicted from QCD FFF2 1978 Parton Distribution Functions Q2 dependence predicted from QCD Quark & Gluon Cross-Sections Calculated from QCD Rick Field - Florida/CDF

  16. QCD ApproachQuarks & Gluons Quark & Gluon Fragmentation Functions Q2 dependence predicted from QCD FFF2 1978 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.” Parton Distribution Functions Q2 dependence predicted from QCD Quark & Gluon Cross-Sections Calculated from QCD Rick Field - Florida/CDF

  17. QCD ApproachQuarks & Gluons FFF2 1978 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.” 30 GeV! Rick Field - Florida/CDF

  18. CDF Run II DiJet EventJuly 2002 ETjet1 = 403 GeV ETjet2 = 322 GeV Raw ET values!! Rick Field - Florida/CDF

  19. Monte-Carlo Simulationof Hadron-Hadron Collisions • At short times (small distances) the color forces are weak and the outgoing partons move away from the beam-beam remnants. • 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. • The resulting event consists of hadrons and leptons in the form of two large transverse momentum outgoing jets plus 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. Rick Field - Florida/CDF

  20. Monte-Carlo Simulationof Hadron-Hadron Collisions FF1-FFF1 (1977) “Black-Box” Model FF2 (1978) Monte-Carlo simulation of “jets” F1-FFF2 (1978) QCD Approach FFFW “FieldJet” (1980) QCD “leading-log order” simulation of hadron-hadron collisions “FF” or “FW” Fragmentation ISAJET (“FF” Fragmentation) PYTHIA HERWIG (“FW” Fragmentation) today Rick Field - Florida/CDF

  21. Monte-Carlo Simulationof Hadron-Hadron Collisions FF1-FFF1 (1977) “Black-Box” Model FF2 (1978) Monte-Carlo simulation of “jets” F1-FFF2 (1978) QCD Approach 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, ....” FFFW “FieldJet” (1980) QCD “leading-log order” simulation of hadron-hadron collisions “FF” or “FW” Fragmentation ISAJET (“FF” Fragmentation) PYTHIA HERWIG (“FW” Fragmentation) today Rick Field - Florida/CDF

  22. The “Underlying Event” inHard 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. Rick Field - Florida/CDF

  23. 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. Min-Bias? • 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 <PT>. • 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). Rick Field - Florida/CDF

  24. Studying the “Underlying Event”at CDF The Underlying Event: beam-beam remnants initial-state radiation multiple-parton interactions • 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. CDF Evolution of Charged Jets Rick Field David Stuart Rich Haas CDF Cone Analysis Valeria Tano Eve Kovacs Joey Huston Anwar Bhatti PRD65:092002, 2002 Ph.D. Thesis Rick Field - Florida/CDF

  25. Evolution of Charged Jets“Underlying Event” Charged Particle Df Correlations PT > 0.5 GeV/c |h| < 1 • Look at charged particle correlations in the azimuthal angle Df relative to the leading charged particle jet. • Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as “Away”. • All three regions have the same size in h-f space, DhxDf = 2x120o = 4p/3. Rick Field - Florida/CDF

  26. Charged Multiplicity versus PT(chgjet#1) • Data on the average number of “toward” (|Df|<60o), “transverse” (60<|Df|<120o), and “away” (|Df|>120o) charged particles (PT > 0.5 GeV, |h| < 1, including jet#1) as a function of the transverse momentum of the leading charged particle jet. Each point corresponds to the <Nchg> 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! Rick Field - Florida/CDF

  27. ISAJET: “Transverse” Nchg versus PT(chgjet#1) • Plot shows the “transverse” <Nchg> vs PT(chgjet#1) compared to the QCD hard scattering predictions of ISAJET 7.32 (default parameters with PT(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). ISAJET Outgoing Jets plus Initial & Final-State Radiation Beam-Beam Remnants Rick Field - Florida/CDF

  28. HERWIG: “Transverse” Nchg versus PT(chgjet#1) • Plot shows the “transverse” <Nchg> vs PT(chgjet#1) compared to the QCD hard scattering predictions of HERWIG 5.9(default parameters with PT(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). HERWIG Outgoing Jets plus Initial & Final-State Radiation Beam-Beam Remnants Rick Field - Florida/CDF

  29. MPI: Multiple PartonInteractions • 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 PT of the hard scattering, PT(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 PT(hard) (single or double Gaussian matter distribution). Rick Field - Florida/CDF

  30. PYTHIA: Multiple PartonInteractions and now HERWIG! Pythia uses multiple parton interactions to enhace the underlying event. Herwig MPI J. M. Butterworth J. R. Forshaw M. H. Seymour Multiple parton interaction more likely in a hard (central) collision! Hard Core Rick Field - Florida/CDF

  31. PYTHIA 6.206 Defaults PYTHIA default parameters • Plot shows “Transverse” <Nchg> versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (PT(hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L. Constant Probability Scattering Default parameters give very poor description of the “underlying event”! Rick Field - Florida/CDF

  32. Tuned PYTHIA 6.206 PYTHIA 6.206 CTEQ5L • Plot shows “Transverse” <Nchg> versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, PARP(67)=1 and PARP(67)=4). Can we distinguish between PARP(67)=1 and PARP(67)=4? New PYTHIA default (less initial-state radiation) New PYTHIA default (less initial-state radiation) Old PYTHIA default (less initial-state radiation) Old PYTHIA default (less initial-state radiation) Rick Field - Florida/CDF

  33. Collider PhenomenologyFrom 7 GeV/c po’s to 400 GeV “Jets” NLO QCD (2002) 400 GeV “jets” FF1 (1977) 7 GeV/c p0’s Rick Field - Florida/CDF

  34. Collider PhenomenologyFrom 7 GeV/c po’s to 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 Q2.” NLO QCD (2002) 400 GeV “jets” Feynman played an enormous role in our understanding of hadron-hadron collisions and his influence is still being felt! FF1 (1977) 7 GeV/c p0’s Rick Field - Florida/CDF

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