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QCD MC Model Tunes: Universal or Energy-specific?

This presentation explores the universality of QCD Monte Carlo model tunes for different center-of-mass energies and hard QCD subprocesses. It also discusses the need for separate tunes for Min-Bias and the underlying event. The data from Tevatron Energy Scan and comparisons with PYTHIA Tune DW are presented.

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QCD MC Model Tunes: Universal or Energy-specific?

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  1. The Next Stretch of the Higgs Magnificent Mile How Universal are the QCD MC Model Tunes? Rick Field University of Florida Outline Chicago May 2012 • How Universal are the QCD MC Model Tunes? • Do we need a separate tune for each center-of-mass energy? 900 GeV, 1.96 TeV, 7 TeV, etc. • Do we need a separate tune for each hard QCD subprocess? Jet Production, Drell-Yan Production, etc. • Do we need separate tunes for “Min-Bias” (MB) and the “underlying event” (UE) in a hard scattering process? • A close look at two PYTHIA tunes: • PYTHIA 6.2 Tune DW (CDF UE tune). • PYTHIA 6.4 Tune Z1 (CMS UE tune). • New CDF UE Data: The Tevatron Energy Scan (300 GeV, 900 GeV, 1.96 TeV). Rick Field – Florida/CDF/CMS

  2. “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

  3. “Hard Scattering” Component QCD Monte-Carlo Models:Lepton-Pair Production • Start with the perturbative Drell-Yan muon pair production and add initial-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). • Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” observables receive contributions from initial-state radiation. Rick Field – Florida/CDF/CMS

  4. Traditional Approach CDF Run 1 Analysis • Look at charged particle correlations in the azimuthal angle Df relative to a leading object (i.e. CaloJet#1, ChgJet#1, PTmax, Z-boson). For CDF PTmin = 0.5 GeV/c hcut = 1. Charged Particle Df Correlations PT > PTmin |h| < hcut Leading Calorimeter Jet or Leading Charged Particle Jet or Leading Charged Particle or Z-Boson “Transverse” region very sensitive to the “underlying event”! • Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as “Away”. • All three regions have the same area in h-f space, Dh×Df = 2hcut×120o = 2hcut×2p/3. Construct densities by dividing by the area in h-f space. Rick Field – Florida/CDF/CMS

  5. “Transverse” Charged Density • Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 1) at 7 TeVas defined by PTmax, PT(chgjet#1), and PT(muon-pair) from PYTHIATune DWat the particle level (i.e. generator level). Charged particle jets are constructed using the Anti-KT algorithm with d = 0.5. Rick Field – Florida/CDF/CMS

  6. 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

  7. PYTHIA Tune DW CMS ATLAS • ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 2.5. The data are corrected and compared with PYTHIA Tune DW at the generator level. • CMS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2. The data are uncorrected and compared with PYTHIA Tune DW after detector simulation. Rick Field – Florida/CDF/CMS

  8. PYTHIA Tune DW Ratio CMS CMS • Ratio of CMS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2. The data are uncorrected and compared with PYTHIA Tune DW after detector simulation. • CMS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2. The data are uncorrected and compared with PYTHIA Tune DW after detector simulation. Rick Field – Florida/CDF/CMS

  9. Charged Particle Density New Large increase in the UE in going from 1.96 TeV to 7 TeV as predicted by PYTHIA Tune DW! • CDF data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for Drell-Yan production as a function of PT(Z) for the “toward”, “away”, and “transverse” regions compared with PYTHIA Tune DW. CMS CDF: Proton-Antiproton Collisions at 1.96 GeV Lepton Cuts: pT > 20 GeV |h| < 1.0 Mass Cut: 70 < M(lepton-pair) < 110 GeV Charged Particles: pT > 0.5 GeV/c |h| < 1.0 CMS: Proton-Proton Collisions at 7 GeV Lepton Cuts: pT > 20 GeV |h| < 2.4 Mass Cut: 60 < M(lepton-pair) < 120 GeV Charged Particles: pT > 0.5 GeV/c |h| < 2.0 • CMS data at 7 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 2 for Drell-Yan production as a function of PT(Z) for the “toward”, “away”, and “transverse” regions compared with PYTHIA Tune DW. Rick Field – Florida/CDF/CMS

  10. PYTHIA Tune DW Overall PYTHIA Tune DW is in amazingly good agreement with the Tevatron Jet production and Drell-Yan data and did a very good job in predicting the LHC Jet production and Drell-Yan data! (although not perfect) CMS Rick Field – Florida/CDF/CMS

  11. CMS UE Data CMS CMS Tune Z1 Tune Z1 • CMS preliminary data at 900 GeV and 7 TeV on the “transverse” charged PTsum density, dPT/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2.0. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. • CMS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2.0. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. CMS corrected data! CMS corrected data! Very nice agreement! Rick Field – Florida/CDF/CMS

  12. ATLAS UE Data ATLAS ATLAS Tune Z1 Tune Z1 • ATLAS published data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 2.5. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. • ATLAS published data at 900 GeV and 7 TeV on the “transverse” charged PTsum density, dPT/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 2.5. The data are corrected and compared with PYTHIA Tune Z1 at the generrator level. ATLAS publication – arXiv:1012.0791 December 3, 2010 Rick Field – Florida/CDF/CMS

  13. CMS-ATLAS UE Data CMS: Chgjet#1 Tune Z1 Tune Z1 ATLAS: PTmax • CMS preliminary data at 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2.0 together with the ATLAS published data at 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 2.5 The data are corrected and compared with PYTHIA Tune Z1 at the generator level. Amazing agreement! Rick Field – Florida/CDF/CMS

  14. Jet Radius Dependence The UE activity is higher for large jet radius! Tune Z1 • The charged particle density in the “transverse” region as defined by the leading charged particle jet from PYTHIA Tune Z1. The charged particles are in the region pT > 0.5 GeV/c and |h| < 2.5. Charged particle jets are constructed using the Anti-KT algorithm with d = 0.2, 0.5, and 1.0 from charged particles in the region pT > 0.5 GeV/c and |h| < 2.5, however, the leading charged particle jet is required to have |h(chgjet#1)| < 1.5. It seems that large jet radius “biases” the UE to be more active! Rick Field – Florida/CDF/CMS

  15. PYTHIA Tune Z1 Tune Z1 describes the energy dependence fairly well! CMS • CDF data at 1.96 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 1 for Drell-Yan production as a function of PT(Z) for the “toward”, “away”, and “transverse” regions compared with PYTHIA Tune Z1. • CMS data at 7 TeV on the density of charged particles, dN/dhdf, with pT > 0.5 GeV/c and |h| < 2 for Drell-Yan production as a function of PT(Z) for the “toward”, “away”, and “transverse” regions compared with PYTHIA Tune Z1. Rick Field – Florida/CDF/CMS

  16. PYTHIA Tune Z1 Tune Z1 Tune Z1 • CMS data at 900 GeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle jet (chgjet#1) for charged particles with pT > 0.5 GeV/c and |h| < 2.0. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. • CDF data at 1.96 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading calorimeter jet (jet#1) for charged particles with pT > 0.5 GeV/c and |h| < 1.0. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. Rick Field – Florida/CDF/CMS

  17. PYTHIA Tune Z1 Overall amazingly good agreement with the LHC and Tevatron Jet production and Drell-Yan! (although not perfect yet) Tune Z1 Tune Z1 What about Min-Bias? Tune Z1 Tune Z1 Rick Field – Florida/CDF/CMS

  18. 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

  19. The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering 1/(pT)4→ 1/(pT2+pT02)2 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

  20. Model of sND Allow leading hard scattering to go to zero pT with same cut-off as the MPI! “Semi-hard” parton-parton collision (pT < ≈2 GeV/c) 1/(pT)4→ 1/(pT2+pT02)2 Model of the inelastic non-diffractive cross section! + + + + … Multiple-parton interactions (MPI)! Rick Field – Florida/CDF/CMS

  21. UE Tunes Allow primary hard-scattering to go to pT = 0 with same cut-off! “Underlying Event” Fit the “underlying event” in a hard scattering process. 1/(pT)4→ 1/(pT2+pT02)2 “Min-Bias” (ND) “Min-Bias” (add single & double diffraction) + + + Predict MB (ND)! + … Predict MB (IN)! Rick Field – Florida/CDF/CMS

  22. Min-Bias Collisions ALICE INEL = NSD + SD NSD = ND + DD CMS Tune Z1 Tune Z1 • CMS NSD data on the charged particle rapidity distribution at 7 TeV compared with PYTHIA Tune Z1. The plot shows the average number of particles per NSD collision per unit h, (1/NNSD) dN/dh. • ALICE NSD data on the charged particle rapidity distribution at 900 GeV compared with PYTHIA Tune Z1. The plot shows the average number of particles per INEL collision per unit h, (1/NINEL) dN/dh. Okay not perfect, but remember we know that SD and DD are not modeled well! Rick Field – Florida/CDF/CMS

  23. MB versus UE Divide be 2p NSD = ND + DD CMS Tune Z1 • CMS NSD data on the charged particle rapidity distribution at 7 TeV compared with PYTHIA Tune Z1. The plot shows the average number of charged particles per NSD collision per unit h, (1/NNSD) dN/dh. • CMS NSD data on the charged particle rapidity distribution at 7 TeV compared with PYTHIA Tune Z1. The plot shows the average number of charged particles per NSD collision per unit h-f, (1/NNSD) dN/dhdf. Rick Field – Florida/CDF/CMS

  24. MB versus UE CMS Tune Z1 NSD = ND + DD Factor of 2! Tune Z1 • Shows the density of charged particles in the “transverse” region as a function of PTmax for charged particles (All pT, |h| < 2) at 7 TeV from PYTHIATune Z1. • CMS NSD data on the charged particle rapidity distribution at 7 TeV compared with PYTHIA Tune Z1. The plot shows the average number of charged particles per NSD collision per unit h-f, (1/NNSD) dN/dhdf. Rick Field – Florida/CDF/CMS

  25. MB versus UE CMS ATLAS Tune Z1 NSD = ND + DD Factor of 2! • ATLAS data on the density of charged particles in the “transverse” region as a function of PTmax for charged particles (pT > 0.1 GeV/c, |h| < 2.5) at 7 TeV compared with PYTHIATune Z1. • CMS NSD data on the charged particle rapidity distribution at 7 TeV compared with PYTHIA Tune Z1. The plot shows the average number of charged particles per NSD collision per unit h-f, (1/NNSD) dN/dhdf. Rick Field – Florida/CDF/CMS

  26. NSD Multiplicity Distribution Difficult to produce enough events with large multiplicity! CMS Tune Z1 • Generator level charged multiplicity distribution (all pT, |h| < 2) at 900 GeV and 7 TeV. Shows the NSD = HC + DD prediction for Tune Z1. Also shows the CMS NSD data. Okay not perfect! But not that bad! Rick Field – Florida/CDF/CMS

  27. MB & UE “Underlying Event” “Min-Bias” CMS CMS Tune Z1 Tune Z1 Difficult to produce enough events with large multiplicity! Difficult to produce enough events with large “transverse” multiplicity at low hard scale! • CMS corrected data at 900 GeV and 7 TeV on the charged particle multiplicity distribution in the “transverse” region for charged particles (pT > 0.5 GeV/c, |h| < 2) as defined by the leading charged particle jet with PT(chgjet#1) > 3 GeV/c compared with PYTHIA Tune Z1 at the generator level. • Generator level charged multiplicity distribution (all pT, |h| < 2) at 900 GeV and 7 TeV. Shows the NSD = HC + DD prediction for Tune Z1. Also shows the CMS NSD data. Rick Field – Florida/CDF/CMS

  28. MB&UE Working Group MB & UE Common Plots CMS ATLAS • The LPCC MB&UE Working Group has suggested several MB&UE “Common Plots” the all the LHC groups can produce and compare with each other. Rick Field – Florida/CDF/CMS

  29. CMS Common Plots Direct charged particles (including leptons) corrected to the particle level with no corrections for SD or DD. Rick Field – Florida/CDF/CMS

  30. ALICE-ATLAS UE ALICE ATLAS Tune Z1 Tune Z1 • ALICE preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 0.8. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. • ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 0.8. The data are corrected and compared with PYTHIA Tune Z1 at the generrator level. Rick Field – Florida/CDF/CMS

  31. ALICE-ATLAS UE Rick Field – Florida/CDF/CMS

  32. Tevatron Energy Scan • Just before the shutdown of the Tevatron CDF has collected more than 10M “min-bias” events at several center-of-mass energies! 900 GeV 300 GeV 1.96 TeV 300 GeV 12.1M MB Events 900 GeV 54.3M MB Events Rick Field – Florida/CDF/CMS

  33. New CDF Energies Tune Z1 • ATLAS preliminary data at 900 GeV and 7 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 0.8. The data are corrected and compared with PYTHIA Tune Z1 at the generator level. • Predictions for CDF on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 0.8 from PYTHIA Tune Z1 at the generator level. Rick Field – Florida/CDF/CMS

  34. CDF Common Plots Rick Field – Florida/CDF/CMS

  35. gmbsar Files = 273 Events = 66,374,130 Size = 803,837,367 KB 1.96 TeV 1 and only 1 Q12 Vertex P0-5 19,420,876 Events 900 GeV 0 or 1 Q12 Vertex 38,306,169 Events • Raw CDF data at 300 GeV, 900 GeV, and 1.96 TeV on the “transverse” charged particle density, dN/dhdf, as defined by the leading charged particle (PTmax) for charged particles with pT > 0.5 GeV/c and |h| < 1.0. 300 GeV 0 or 1 Q12 Vertex 7,484,514 Events Rick Field – Florida/CDF/CMS

  36. PARP(82) PARP(90) Color Diffraction Connections How Universal are the Tunes? What we are learning should allow for more precise predictions at future LHC energies (10 TeV, 13 TeV)! • Do we need a separate tune for each center-of-mass energy? 900 GeV, 1.96 TeV, 7 TeV, etc. PYTHIA Tune DW did a nice (although not perfect) job predicting the LHC Jet Production and Drell-Yan UE data. I am still hoping for a single tune that will describe all energies! Tune Z1 also very good! Soon we will have UE data at 300 GeV, 900 GeV, 1.96 TeV, 7 TeV, & 8 TeV and can map out the energy dependence! • Do we need a separate tune for eachhard QCD subprocess? Jet Production, Drell-Yan Production, etc. The same tune can describe both Jet Production and Drell-Yan! • Do we need separate tunes for “Min-Bias” (MB) and the “underlying event” (UE) in a hard scattering process? PHTHIA Tune Z1 does fairly well at both the UE and MB, but you cannot expect such a naïve approach to be perfect! Rick Field – Florida/CDF/CMS

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