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

Predicting “Min-Bias” and the “Underlying Event” at the LHC. Important 900 GeV Measurements. Rick Field University of Florida. Outline of Talk. The inelastic non-diffractive cross section. New CDF charged multiplicity distribution and comparisons with the QCD Monte-Carlo tunes.

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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 Important 900 GeV Measurements Rick Field University of Florida Outline of Talk • The inelastic non-diffractive cross section. • New CDF charged multiplicity distribution and comparisons with the QCD Monte-Carlo tunes. CERN November 10, 2009 • Relationship between the “underlying event” in a hard scattering process and “min-bias” collisions. CDF Run 2 • “Min-Bias at 900 GeV and 2.2 TeV. • The “underlying event” at 900 GeV and 7 TeV. UE&MB@CMS CMS at the LHC • Summary. Rick Field – Florida/CDF/CMS

  2. 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+sHC • 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

  3. 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

  4. 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! No MPI! Tune S320! • The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI). Rick Field – Florida/CDF/CMS

  5. 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

  6. 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

  7. 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

  8. Charged Particle Multiplicity The charged multiplicity distribution does not change between 1.96 and 2.2 TeV and proton-proton is the same as proton-antiproton! • 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. The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (pyAnoMPI). Tune A prediction at 900 GeV! Tune A prediction at 2.2 TeV! Tune A! No MPI! • Prediction from PYTHIA Tune A for proton-proton collisions at 900 GeV and 2.2 TeV. Rick Field – Florida/CDF/CMS

  9. LHC Predictions: 900 GeV • Charged multiplicity distributions for proton-proton collisions at 900 GeV (|h| < 2) from PYTHIA Tune A, Tune DW, Tune S320, and Tune P329. Rick Field – Florida/CDF/CMS

  10. “Transverse” Charged Density PTmax > 5 GeV/c! • 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). • Shows the charged particle multiplicity distribution in the “transverse” region (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

  11. Charged Particle Multiplicity NchgDen = 0.21 The “underlying event” is twice as active as an average HC collision! • Shows the charged particle multiplicity distribution in the “transverse” region (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). • Shows the charged particle multiplicity distribution in HC collisions (pT > 0.5 GeV/c, |h| < 2) at 900 GeVPYTHIATune A,Tune DW, Tune S320, and Tune P329 at the particle level (i.e. generator level). Rick Field – Florida/CDF/CMS

  12. sHC: PTmax > 5 GeV/c • The inelastic non-diffractive PTmax > 5 GeV/c cross section (|h| < 1) versus center-of-mass energy from PYTHIA (×1.2). Still lots of events! Log scale! Linear scale! stot = sEL + sSD+sDD+sHC In 1,000,000 HC collisions at 900 GeV you get 940 with PTmax > 5 GeV/c! • sHC(PTmax > 5 GeV/c) varies more rapidly. Factor of 2.3 increase between 7 TeV (≈ 0.56 mb) and 14 teV (≈ 1.3 mb). Linear on a linear scale! Rick Field – Florida/CDF/CMS

  13. PTmax Cross-Section 900 GeV If we get 3,400,000 HC collisions at 900 GeV we could do both “min-bias” AND the “underlying event” and compare them! Very important to do BOTH “soft” and “hard” physics! • The inelastic non-diffractive PTmax > 5 GeV/c cross section (|h| < 2) at 900 GeV from PYTHIA Tune DW and Tune S320. In 1,000,000 HC collisions at 900 GeV you get ~3,000 with PTmax > 5 GeV/c! stot = sEL + sSD+sDD+sHC Need about 10,000 HC events with PTmax > 5 GeV/c to do a nice analysis! • Number of events with PTmax > PT0 (|h| < 2) for 1,000,000 HC collisions at 900 GeV from PYTHIA Tune DW and Tune S320. Rick Field – Florida/CDF/CMS

  14. 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

  15. 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

  16. “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

  17. Important 900 GeV Measurements It is very important to measure BOTH “min-bias” and the and the “underlying event” at 900 GeV! To do this we need to collect about 5,000,000 CMS min-bias triggers! • The amount of activity in “min-bias” collisions (multiplicity distribution, pT distribution, PTsum distribution, dNchg/dh). For every 1,000 events here We get 3 events here! • The amount of activity in the “underlying event” in hard scattering events (“transverse” Nchg distribution, “transverse” pT distribution, “transverse” PTsum distribution for events with PTmax > 5 GeV/c). • We should map out the energy dependence of the “underlying event” in a hard scattering process from 900 GeV to 14 TeV! Rick Field – Florida/CDF/CMS

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