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Predicting “Min-Bias” and the “Underlying Event” at the LHC

Predicting “Min-Bias” and the “Underlying Event” at the LHC. Extrapolations from the Tevatron to RHIC and the LHC. Rick Field University of Florida. Outline of Talk. Review of the CDF PYTHIA Tunes. The PYTHIA MPI energy scaling parameter PARP(90). CERN March 2, 2010.

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Predicting “Min-Bias” and the “Underlying Event” at the LHC

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  1. Predicting “Min-Bias” and the “Underlying Event” at the LHC Extrapolations from the Tevatron to RHIC and the LHC Rick Field University of Florida Outline of Talk • Review of the CDF PYTHIA Tunes. • The PYTHIA MPI energy scaling parameter PARP(90). CERN March 2, 2010 • The “underlying event” at STAR. Extrapolations to RHIC. CDF Run 2 • Predicting MB from the activity in the UE. Relationship between MB and the UE. • How precise is precise? • Associated Density Df plots. UE&MB@CMS • QCD Monte-Carlo Models - Overall Goal. CMS at the LHC Rick Field – Florida/CDF/CMS

  2. Proton-Proton Collisions stot = sEL + sSD+sDD+sHC ND “Inelastic Non-Diffractive Component” The “hard core” component contains both “hard” and “soft” collisions. Rick Field – Florida/CDF/CMS

  3. Inelastic Non-Diffractive Cross-Section • The inelastic non-diffractive cross section versus center-of-mass energy from PYTHIA (×1.2). My guess! Linear scale! Log scale! stot = sEL + sSD+sDD+sND • sHC varies slowly. Only a 13% increase between 7 TeV (≈ 58 mb) and 14 teV (≈ 66 mb). Linear on a log scale! Rick Field – Florida/CDF/CMS

  4. “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

  5. 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

  6. 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

  7. Tuning PYTHIA:Multiple Parton Interaction Parameters Hard Core Determines the energy dependence of the MPI! 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

  8. “Transverse” Conesvs “Transverse” Regions • Sum the PT of charged particles in two cones of radius 0.7 at the same h as the leading jet but with |DF| = 90o. • Plot the cone with the maximum and minimum PTsum versus the ET of the leading (calorimeter) jet. “Cone Analysis” (Tano, Kovacs, Huston, Bhatti) Transverse Cone: p(0.7)2=0.49p Transverse Region: 2p/3=0.67p Rick Field – Florida/CDF/CMS

  9. Energy Dependenceof the “Underlying Event” “Cone Analysis” (Tano, Kovacs, Huston, Bhatti) • Sum the PT of charged particles (pT > 0.4 GeV/c) in two cones of radius 0.7 at the same h as the leading jet but with |DF| = 90o. Plot the cone with the maximum and minimum PTsum versus the ET of the leading (calorimeter) jet. • Note that PYTHIA 6.115 is tuned at 630 GeV with PT0 = 1.4 GeV and at 1,800 GeV with PT0 = 2.0 GeV. This implies that e = PARP(90) should be around 0.30 instead of the 0.16 (default). • For the MIN cone 0.25 GeV/c in radius R = 0.7 implies a PTsum density of dPTsum/dhdf = 0.16 GeV/c and 1.4 GeV/c in the MAX cone implies dPTsum/dhdf = 0.91 GeV/c (average PTsum density of 0.54 GeV/c per unit h-f). 630 GeV 1,800 GeV PYTHIA 6.115 PT0 = 1.4 GeV PYTHIA 6.115 PT0 = 2.0 GeV Rick Field – Florida/CDF/CMS

  10. “Transverse” Charged DensitiesEnergy Dependence Rick Field Fermilab MC Workshop October 4, 2002! Increasing e produces less energy dependence for the UE resulting in less UE activity at the LHC! Lowering PT0 at 630 GeV (i.e. increasing e) increases UE activity resulting in less energy dependence. • Shows the “transverse” charged PTsum density (|h|<1, PT>0.4 GeV) versus PT(charged jet#1) at 630 GeV predicted by HERWIG 6.4 (PT(hard) > 3 GeV/c, CTEQ5L) and a tuned version of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L, Set A, e = 0, e = 0.16 (default) and e = 0.25 (preferred)). • Also shown are the PTsum densities (0.16 GeV/c and 0.54 GeV/c) determined from the Tano, Kovacs, Huston, and Bhatti “transverse” cone analysis at 630 GeV. Reference point E0 = 1.8 TeV Rick Field – Florida/CDF/CMS

  11. 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

  12. CDF Run 1 PT(Z) Tune used by the CDF-EWK group! PYTHIA 6.2 CTEQ5L • Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune A (<pT(Z)> = 9.7 GeV/c), and PYTHIA Tune AW (<pT(Z)> = 11.7 GeV/c). UE Parameters ISR Parameters Effective Q cut-off, below which space-like showers are not evolved. Intrensic KT The Q2 = kT2 in as for space-like showers is scaled by PARP(64)! Rick Field – Florida/CDF/CMS

  13. Df Jet#1-Jet#2 Jet#1-Jet#2 Df Distribution Jet-Jet Correlations (DØ) • MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5) • L= 150 pb-1 (Phys. Rev. Lett. 94 221801 (2005)) • Data/NLO agreement good. Data/HERWIG agreement good. • Data/PYTHIA agreement good provided PARP(67) = 1.0→4.0 (i.e. like Tune A, best fit 2.5). Rick Field – Florida/CDF/CMS

  14. CDF Run 1 PT(Z) PYTHIA 6.2 CTEQ5L • Shows the Run 1 Z-boson pT distribution (<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA Tune DW, and HERWIG. UE Parameters ISR Parameters Tune DW uses D0’s perfered value of PARP(67)! Intrensic KT Tune DW has a lower value of PARP(67) and slightly more MPI! Rick Field – Florida/CDF/CMS

  15. PYTHIA 6.2 Tunes None of the CDF Tunes included any “min-bias” data in the determination of the parameters! All use LO as with L = 192 MeV! UE Parameters Uses CTEQ6L Tune A energy dependence! ISR Parameter Intrinsic KT Rick Field – Florida/CDF/CMS

  16. PYTHIA 6.2 Tunes These are “old” PYTHIA 6.2 tunes! There are new 6.420 tunes by Peter Skands (Tune S320, update of S0) Peter Skands (Tune N324, N0CR) Hendrik Hoeth (Tune P329, “Professor”) All use LO as with L = 192 MeV! UE Parameters Tune B Tune AW Tune BW Tune A ATLAS energy dependence! ISR Parameter Tune DW Tune D6 Tune D Tune D6T Intrinsic KT CMS Rick Field – Florida/CDF/CMS

  17. “Towards”, “Away”, “Transverse” Look at the charged particle density, the charged PTsum density and the ETsum density in all 3 regions! • Look at correlations in the azimuthal angle Df relative to the leading charged particle jet (|h| < 1) or the leading calorimeter jet (|h| < 2). • Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse ”, and |Df| > 120o as “Away”. Each of the three regions have area DhDf = 2×120o = 4p/3. Df Correlations relative to the leading jet Charged particles pT > 0.5 GeV/c |h| < 1 Calorimeter towers ET > 0.1 GeV |h| < 1 “Transverse” region is very sensitive to the “underlying event”! Z-Boson Direction Rick Field – Florida/CDF/CMS

  18. Event Topologies • “Leading Jet” events correspond to the leading calorimeter jet (MidPoint R = 0.7) in the region |h| < 2 with no other conditions. “Leading Jet” subset • “Inclusive 2-Jet Back-to-Back” events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (Df12 > 150o) with almost equal transverse energies (PT(jet#2)/PT(jet#1) > 0.8) with no other conditions . “Inc2J Back-to-Back” subset “Exc2J Back-to-Back” • “Exclusive 2-Jet Back-to-Back” events are selected to have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (Df12 > 150o) with almost equal transverse energies (PT(jet#2)/PT(jet#1) > 0.8) and PT(jet#3) < 15 GeV/c. “Charged Jet” • “Leading ChgJet” events correspond to the leading charged particle jet (R = 0.7) in the region |h| < 1 with no other conditions. • “Z-Boson” events are Drell-Yan events with 70 < M(lepton-pair) < 110 GeV with no other conditions. Z-Boson Rick Field – Florida/CDF/CMS

  19. Observables at theParticle and Detector Level “Leading Jet” “Back-to-Back” Rick Field – Florida/CDF/CMS

  20. “Towards”, “Away”, “Transverse” • Data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “leading jet” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A at the particle level (i.e. generator level). “Leading Jet” Factor of ~13 Factor of ~16 Factor of ~4.5 • Data at 1.96 TeV on the charged particle scalar pT sum density, dPT/dhdf, with pT > 0.5 GeV/c and |h| < 1 for “leading jet” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A at the particle level (i.e. generator level). • Data at 1.96 TeV on the particle scalar ET sum density, dET/dhdf, for |h| < 1 for “leading jet” events as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A at the particle level (i.e. generator level). Rick Field – Florida/CDF/CMS

  21. “Transverse” Charged Density 0.6 • Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 1) at 1.96 TeVas defined by PTmax, PT(chgjet#1), and PT(jet#1) from PYTHIATune Aat the particle level (i.e. generator level). Rick Field – Florida/CDF/CMS

  22. Min-Bias “Associated”Charged Particle Density 35% more at RHIC means 26% less at the LHC! • Shows the “associated” charged particle density in the “transverse” regions as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV and 14 TeVfrom PYTHIA Tune DW and Tune DWT at the particle level (i.e. generator level). The STAR data from RHIC favors Tune DW! ~1.35 ~1.35 0.2 TeV → 14 TeV (~factor of 70 increase) RHIC LHC Rick Field – Florida/CDF/CMS

  23. Min-Bias “Associated”Charged Particle Density • Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 1.96 TeV and 14 TeVpredicted by PYTHIA Tune DW at the particle level (i.e. generator level). ~1.9 ~2.7 0.2 TeV → 1.96 TeV (UE increase ~2.7 times) 1.96 TeV → 14 TeV (UE increase ~1.9 times) RHIC LHC Tevatron Rick Field – Florida/CDF/CMS

  24. The “Underlying Event” at STAR • At STAR they have measured the “underlying event at W = 200 GeV (|h| < 1, pT > 0.2 GeV) and compared their uncorrected data with PYTHIA Tune A + STAR-SIM. Rick Field – Florida/CDF/CMS

  25. Preliminary The “Underlying Event” at STAR Charged PTsum Density “Back-to-Back” Charged Particles (|h|<1.0, PT>0.2 GeV/c) Data uncorrected PYTHIA Tune A + STAR-SIM “Toward” 0.55 “Away” ~1.5 “Transverse” 0.37 “Leading Jet” PT(jet#1) (GeV/c) “Back-to-Back” • Data on the charged particle scalar pT sum density, dPT/dhdf, as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions compared with PYTHIA Tune A. Rick Field – Florida/CDF/CMS

  26. Min-Bias “Associated”Charged Particle Density • Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeVpredicted by PYTHIA Tune DW at the particle level (i.e. generator level). LHC14 LHC10 LHC7 Tevatron 900 GeV RHIC 0.2 TeV → 1.96 TeV (UE increase ~2.7 times) 1.96 TeV → 14 TeV (UE increase ~1.9 times) RHIC LHC Tevatron Linear scale! Rick Field – Florida/CDF/CMS

  27. Min-Bias “Associated”Charged Particle Density • Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2 TeV, 0.9 TeV, 1.96 TeV, 7 TeV, 10 TeV, 14 TeVpredicted by PYTHIA Tune DW at the particle level (i.e. generator level). LHC14 LHC10 LHC7 Tevatron 900 GeV RHIC 7 TeV → 14 TeV (UE increase ~20%) LHC7 LHC14 Linear on a log plot! Log scale! Rick Field – Florida/CDF/CMS

  28. “Transverse” Charge Density factor of 2! 900 GeV → 7 TeV (UE increase ~ factor of 2.1) LHC 900 GeV LHC 7 TeV • Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 2) at 900 GeVas defined by PTmax from PYTHIATune DW and Tune S320 at the particle level (i.e. generator level). Rick Field – Florida/CDF/CMS

  29. “Transverse” Charged Particle Density • Fake data (from MC) at 900 GeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2. The fake data (from PYTHIA Tune DW) are generated at the particle level (i.e. generator level) assuming 0.5 M min-bias events at 900 GeV (361,595 events in the plot). 361,595 events • Fake data (from MC) at 900 GeV on the “transverse” charged PTsum density, dPT/dhdf, as defined by the leading charged particle (PTmax) and the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2. The fake data (from PYTHIA Tune DW) are generated at the particle level (i.e. generator level) assuming 0.5 M min-bias events at 900 GeV (361,595 events in the plot). Talk by Edward Wenger Yesterday Rick Field – Florida/CDF/CMS

  30. PYTHIA Tune A Min-Bias“Soft” + ”Hard” Tuned to fit the CDF Run 1 “underlying event”! PYTHIA Tune A CDF Run 2 Default 12% of “Min-Bias” events have PT(hard) > 5 GeV/c! 1% of “Min-Bias” events have PT(hard) > 10 GeV/c! • 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. 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

  31. Charged Particle Multiplicity New • Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2. Tune A! No MPI! 7 decades! • The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI). Rick Field – Florida/CDF/CMS

  32. The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering Hard parton-parton collisions is hard (pT > ≈2 GeV/c) “Semi-hard” parton-parton collision (pT < ≈2 GeV/c) The “underlying-event” (UE)! + + + … Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”. Multiple-parton interactions (MPI)! Rick Field – Florida/CDF/CMS

  33. The Inelastic Non-Diffractive Cross-Section Occasionally one of the parton-parton collisions is hard (pT > ≈2 GeV/c) Majority of “min-bias” events! “Semi-hard” parton-parton collision (pT < ≈2 GeV/c) + + + + … Multiple-parton interactions (MPI)! Rick Field – Florida/CDF/CMS

  34. The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering Hard parton-parton collisions is hard (pT > ≈2 GeV/c) “Semi-hard” parton-parton collision (pT < ≈2 GeV/c) The “underlying-event” (UE)! + + + … Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”. Multiple-parton interactions (MPI)! Rick Field – Florida/CDF/CMS

  35. Charged Particle Multiplicity • Data at 1.96 TeV on the charged particle multiplicity (pT > 0.4 GeV/c, |h| < 1) for “min-bias” collisions at CDF Run 2. Tune A prediction at 900 GeV! No MPI! Tune A! • The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI). • Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV. Rick Field – Florida/CDF/CMS

  36. LHC Predictions: 900 GeV • Compares the 900 GeV data with my favorite PYTHIA Tunes (Tune DW and Tune S320 Perugia 0). Tune DW uses the old Q2-ordered parton shower and the old MPI model. Tune S320 uses the new pT-ordered parton shower and the new MPI model. The numbers in parentheses are the average value of dN/dh for the region |h| < 0.6. Rick Field – Florida/CDF/CMS

  37. LHC Predictions: 900 GeV Off by 11%! CMS dN/dh • Shows the individual HC, DD, and SD predictions of PYTHIA Tune DW and Tune S320 Perugia 0. The numbers in parentheses are the average value of dN/dh for the region |h| < 0.6. I do not trust PYTHIA to model correctly the DD and SD contributions! I would like to know how well these tunes model the HC component. We need to look at observables where only HC contributes! Rick Field – Florida/CDF/CMS

  38. “Transverse” Charged Particle Density A Closer Look! Room for 10% increase! • Data at 1.96 TeV on the charged particle density, with pT > 0.5 GeV/c and |h| < 1 for the “transverse” region for “Leading Jet” events as a function of the leading jet pT. The data are corrected to the particle level (with errors that include both the statistical error and the systematic uncertainty) and are compared with PYTHIA Tune A and HERWIG (without MPI) at the generator level (i.e. particle level). Rick Field – Florida/CDF/CMS

  39. PYTHIA Tune X1 • Tune X1 (modify Tune DW slightly, PYTHIA 6.42). Uses old Q2 ordered shower and old UE model. 10% increase at Tevatron! 20% increase at 900 GeV! 22% increase at 200 GeV! Change pT0 = PARP(82) slightly at the Tevtron. Change e = PARP(90). Change color connection back to those in Tune A. Rick Field – Florida/CDF/CMS

  40. Preliminary The “Underlying Event” at STAR A Closer Look! Charged Particle Density “Back-to-Back” Charged Particles (|h|<1.0, PT>0.2 GeV/c) Data uncorrected PYTHIA Tune A + STAR-SIM “Toward” “Away” “Transverse” Room for 30% increase! PT(jet#1) (GeV/c) “Back-to-Back” • Data at 200 GeV on the charged particle density, dN/dhdf, as a function of the leading jet pT for the “toward”, “away”, and “transverse” regions compared with PYTHIA Tune A. Rick Field – Florida/CDF/CMS

  41. LHC Predictions: 900 GeV 10% increase at 900 GeV! • Shows the individual HC, DD, and SD predictions of PYTHIA Tune DW and Tune S320 Perugia 0. The numbers in parentheses are the average value of dN/dh for the region |h| < 0.6 Better! But not perfect! Rick Field – Florida/CDF/CMS

  42. 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

  43. 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

  44. Min-Bias “Associated”Charged Particle Density PY Tune A PTmax > 2.0 GeV/c Transverse Region Transverse Region 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 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”). Rick Field – Florida/CDF/CMS

  45. Min-Bias “Associated”Charged PTsum Density PY Tune A PTmax > 2.0 GeV/c Transverse Region Transverse Region PTmax > 0.5 GeV/c • Shows the data on the Df dependence of the “associated” charged PTsum density, dPTsum/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 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”). Rick Field – Florida/CDF/CMS

  46. “Associated” Charged Particle Density • Shows the Df dependence of the “associated” charged particle density, dNchg/dhdf, for charged particles (pT > 0.5 GeV/c, |h| < 2, not including PTmax) relative to PTmax at 900 GeVwith PTmax > 2.0 GeV/c from PYTHIA Tune DW,Tune DWPro, andTune S320(generator level). PY Tune DW PY Tune DWPro PY Tune S320 Rick Field – Florida/CDF/CMS

  47. My Dream! The Goal – QCD MC Stay tuned! UE studies at 900 GeV coming soon from CMS and ATLAS. • Do not want a separate MC tune for MB at each energy (200 GeV. 630 GeV, 900 GeV, 1.96 TeV, and 7 TeV)! Want “universal” tune that predicts correctly the energy dependence of MB! • Do not want a separate MC tune for the UE at each energy (200 GeV. 630 GeV, 900 GeV, 1.96 TeV, and 7 TeV)! Want “universal” tune that predicts correctly the energy dependence of the UE! • Do not want a separate tune for PTmax, PT(jet), and Drell-Yan! Want “universal” tune for all hard scattering processes! • Do not want a separate tune for MB and the UE! Want “universal” tune that describes both MB and the UE! How precise does this have to be before one considers it a great success? Rick Field – Florida/CDF/CMS

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