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Toward an Understanding of Hadron-Hadron Collisions

Toward an Understanding of Hadron-Hadron Collisions. From Feynman-Field to the LHC. Rick Field University of Florida. Outline of Talk. LBNL January 15, 2009. Before Feynman-Field Phenomenology. The early days of Feynman-Field Phenomenology.

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Toward an Understanding of Hadron-Hadron Collisions

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

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

  3. Before Feynman-Field Rick & Jimmie 1970 Rick & Jimmie 1968 Rick & Jimmie 1972 (pregnant!) Rick & Jimmie at CALTECH 1973 Rick Field – Florida/CDF/CMS

  4. Feynman-Field Phenomenology Toward and Understanding of Hadron-Hadron Collisions 1st hat! Feynman and Field • From 7 GeV/c p0’s to 600 GeV/c Jets. The early days of trying to understand and simulate hadron-hadron collisions. Rick Field – Florida/CDF/CMS

  5. The Feynman-Field Days 1973-1983 • 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). “Feynman-Field Jet Model” • 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/CMS

  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/CMS

  7. Quark-Quark Black-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/CMS

  8. Quark-Quark Black-Box Model FF1 1977 (preQCD) Predict increase with increasing CM energy W Predict particle ratios “Beam-Beam Remnants” Predict overall event topology (FFF1 paper 1977) 7 GeV/c p0’s! Rick Field – Florida/CDF/CMS

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

  10. Letter from Feynman July 1976 Rick Field – Florida/CDF/CMS

  11. Letter from Feynman Page 1 Spelling? Rick Field – Florida/CDF/CMS

  12. Letter from Feynman Page 3 It is fun! Onward! Rick Field – Florida/CDF/CMS

  13. Feynman Talk at Coral Gables(December 1976) 1st transparency Last transparency “Feynman-Field Jet Model” Rick Field – Florida/CDF/CMS

  14. QCD Approach: Quarks & 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/CMS

  15. (bk) (ka) (cb) (ba) cc pair bb pair A Parameterization of the Properties of Jets • Assumed that jets could be analyzed on a “recursive” principle. Field-Feynman 1978 Secondary Mesons (after decay) • Let f(h)dh be the probability that the rank 1 meson leaves fractional momentum h to the remaining cascade, leaving quark “b” with momentum P1 = h1P0. Rank 2 Rank 1 • 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(h)), leaving quark “c” with momentum P2 = h2P1 = h2h1P0. Primary Mesons continue • Add in flavor dependence by letting bu = probabliity of producing u-ubar pair, bd = probability of producing d-dbar pair, etc. Calculate F(z) from f(h) and bi! • 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. Original quark with flavor “a” and momentum P0 Rick Field – Florida/CDF/CMS

  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, ....” Rick Field – Florida/CDF/CMS

  17. 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 the past today ISAJET (“FF” Fragmentation) HERWIG (“FW” Fragmentation) PYTHIA tomorrow SHERPA PYTHIA 6.4 Rick Field – Florida/CDF/CMS

  18. High PT Jets CDF (2006) Feynman, Field, & Fox (1978) Predict large “jet” cross-section 30 GeV/c! 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 PT discussed here.” 600 GeV/c Jets! Rick Field – Florida/CDF/CMS

  19. CDF DiJet Event: M(jj) ≈ 1.4 TeV ETjet1 = 666 GeV ETjet2 = 633 GeV Esum = 1,299 GeV M(jj) = 1,364 GeV M(jj)/Ecm≈ 70%!! Rick Field – Florida/CDF/CMS

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

  21. Proton-AntiProton Collisionsat the Tevatron The CDF “Min-Bias” trigger picks up most of the “hard core” cross-section plus a small amount of single & double diffraction. stot = sEL + sIN stot = sEL + sSD+sDD+sHC 1.8 TeV: 78mb = 18mb + 9mb + (4-7)mb + (47-44)mb CDF “Min-Bias” trigger 1 charged particle in forward BBC AND 1 charged particle in backward BBC The “hard core” component contains both “hard” and “soft” collisions. Beam-Beam Counters 3.2 < |h| < 5.9 Rick Field – Florida/CDF/CMS

  22. “Hard Scattering” Component 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). “Underlying Event” • The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or semi-soft multiple parton interactions (MPI). The “underlying event” is an unavoidable background to most collider observables and having good understand of it leads to more precise collider measurements! • Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” observables receive contributions from initial and final-state radiation. Rick Field – Florida/CDF/CMS

  23. 3 charged particles dNchg/dhdf = 3/4p = 0.24 1 charged particle Divide by 4p 1 GeV/c PTsum dNchg/dhdf = 1/4p = 0.08 3 GeV/c PTsum dPTsum/dhdf = 1/4p GeV/c = 0.08 GeV/c dPTsum/dhdf = 3/4p GeV/c = 0.24 GeV/c Particle Densities • Study the charged particles (pT > 0.5 GeV/c, |h| < 1) and form the charged particle density, dNchg/dhdf, and the charged scalar pT sum density, dPTsum/dhdf. Charged Particles pT > 0.5 GeV/c |h| < 1 CDF Run 2 “Min-Bias” DhDf = 4p = 12.6 Rick Field – Florida/CDF/CMS

  24. CDF Run 1 Min-Bias “Associated”Charged Particle Density “Associated” densities do not include PTmax! Highest pT charged particle! • Use the maximum pT charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dNchg/dhdf, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1). It is more probable to find a particle accompanying PTmax than it is to find a particle in the central region! • Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged particle density, dNchg/dhdf, for “min-bias” events. Rick Field – Florida/CDF/CMS

  25. CDF Run 1 Min-Bias “Associated”Charged Particle Density Rapid rise in the particle density in the “transverse” region as PTmax increases! PTmax > 2.0 GeV/c Transverse Region Transverse Region Ave Min-Bias 0.25 per unit h-f PTmax > 0.5 GeV/c • Shows the data on the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” eventswith PTmax > 0.5, 1.0, and 2.0 GeV/c. • Shows “jet structure” in “min-bias” collisions (i.e.the “birth” of the leading two jets!). Rick Field – Florida/CDF/CMS

  26. CDF Run 1: Evolution of Charged Jets“Underlying Event” • 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. Charged Particle Df Correlations PT > 0.5 GeV/c |h| < 1 Look at the charged particle density in the “transverse” region! “Transverse” region very sensitive to the “underlying event”! CDF Run 1 Analysis Rick Field – Florida/CDF/CMS

  27. Factor of 2! Run 1 Charged Particle Density“Transverse” pT Distribution • Compares the average “transverse” charge particle density with the average “Min-Bias” charge particle density (|h|<1, pT>0.5 GeV). Shows how the “transverse” charge particle density and the Min-Bias charge particle density is distributed in pT. PT(charged jet#1) > 30 GeV/c “Transverse” <dNchg/dhdf> = 0.56 “Min-Bias” CDF Run 1 Min-Bias data <dNchg/dhdf> = 0.25 Rick Field – Florida/CDF/CMS

  28. ISAJET 7.32“Transverse” Density ISAJET uses a naïve leading-log parton shower-model which does not agree with the data! • Plot shows average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus PT(charged jet#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 “Hard” Component Beam-Beam Remnants Rick Field – Florida/CDF/CMS

  29. HERWIG 6.4“Transverse” Density • Plot shows average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus PT(charged jet#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 uses a modified leading-log parton shower-model which does agrees better with the data! HERWIG “Hard” Component Beam-Beam Remnants Rick Field – Florida/CDF/CMS

  30. 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/CMS

  31. Tuning PYTHIA:Multiple Parton Interaction Parameters Hard Core Determine by comparing with 630 GeV data! Affects the amount of initial-state radiation! Take E0 = 1.8 TeV Reference point at 1.8 TeV Rick Field – Florida/CDF/CMS

  32. PYTHIA 6.206 Defaults MPI constant probability scattering • Plot shows the “Transverse” charged particle density 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. PYTHIA default parameters Default parameters give very poor description of the “underlying event”! Note Change PARP(67) = 4.0 (< 6.138) PARP(67) = 1.0 (> 6.138) Rick Field – Florida/CDF/CMS

  33. Run 1 PYTHIA Tune A CDF Default! • Plot shows the “transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set B (PARP(67)=1)andSet A(PARP(67)=4)). PYTHIA 6.206 CTEQ5L Run 1 Analysis Old PYTHIA default (more initial-state radiation) Old PYTHIA default (more initial-state radiation) New PYTHIA default (less initial-state radiation) New PYTHIA default (less initial-state radiation) Rick Field – Florida/CDF/CMS

  34. Run 1 vs Run 2: “Transverse” Charged Particle Density “Transverse” region as defined by the leading “charged particle jet” • Shows the data on the average “transverse” charge particle density (|h|<1, pT>0.5 GeV) as a function of the transverse momentum of the leading charged particle jet from Run 1. Excellent agreement between Run 1 and 2! • 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. 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). Rick Field – Florida/CDF/CMS

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

  36. Min-Bias Correlations New • Data at 1.96 TeV on the average pT of charged particles versus the number of charged particles (pT > 0.4 GeV/c, |h| < 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). Rick Field – Florida/CDF/CMS

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

  38. Average PT versus Nchg • Data at 1.96 TeV on the average pT of charged particles versus the number of charged particles (pT > 0.4 GeV/c, |h| < 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 pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. Rick Field – Florida/CDF/CMS

  39. Average PT versus Nchg No MPI! • Z-boson production (with low pT(Z) and no MPI) produces low multiplicity and small <pT>. • High pT Z-boson production produces large multiplicity and high <pT>. • Z-boson production (with MPI) produces large multiplicity and medium <pT>. = + + Rick Field – Florida/CDF/CMS

  40. Average PT(Z) versus Nchg No MPI! • Predictions for the average PT(Z-Boson) versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV) at CDF Run 2. • Data on the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 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). Rick Field – Florida/CDF/CMS

  41. Average PT versus Nchg PT(Z) < 10 GeV/c No MPI! Remarkably similar behavior! Perhaps indicating that MPI playing an important role in both processes. • Predictions for the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, PT(pair) < 10 GeV/c) at CDF Run 2. • Data the average pT of charged particles versus the number of charged particles (pT > 0.5 GeV/c, |h| < 1, excluding the lepton-pair) for for Drell-Yan production (70 < M(pair) < 110 GeV, PT(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). Rick Field – Florida/CDF/CMS

  42. DWT UE&MB@CMS 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 andmuons for Drell-Yan) • 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) Study the “underlying event” by using charged particles and muons! (start as soon as possible) Shapes of the pT(m+m-) distribution at the Z-boson mass. <pT(m+m-)> is much larger at the LHC! • Drell-Yan Studies: Transverse momentum distribution of the lepton-pair versus the mass of the lepton-pair, <pT(pair)>, <pT2(pair)>, ds/dpT(pair) (only requires muons). Event structure for large lepton-pair pT (i.e.mm +jets, requires muons). Rick Field – Florida/CDF/CMS

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