Predicting MinBias and the Underlying Event at the
Predicting “Min-Bias” and the “Underlying Event” at the LHC Important 900 Ge. V Measurements Rick Field University of Florida Outline of Talk Æ The inelastic non-diffractive cross section. Æ New CDF charged multiplicity CERN November 10, 2009 distribution and comparisons with the QCD Monte-Carlo tunes. Æ Relationship between the “underlying event” in a hard scattering process and “min-bias” collisions. CDF Run 2 Æ “Min-Bias at 900 Ge. V and 2. 2 Te. V. Æ The “underlying event” at 900 Ge. V and 7 Te. V. Æ Summary. CMS-QCD Group Meeting November 10, 2009 CMS at the LHC Rick Field – Florida/CDF/CMS UE&MB@CMS 1
Inelastic Non-Diffractive Cross-Section My guess! Linear scale! Log scale! stot = s. EL + s. SD + s. DD + s. HC Æ The inelastic non-diffractive cross section versus center-of-mass energy from PYTHIA (× 1. 2). Æs. HC varies slowly. Only a 13% increase between 7 Te. V (≈ 58 mb) and 14 te. V (≈ 66 mb). Linear on a log scale! CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 2
Charged Particle Multiplicity 7 decades! No MPI! Tune A! Æ Data at 1. 96 Te. V on the charged particle multiplicity (p. T > 0. 4 Ge. V/c, |h| < 1) for “min-bias” collisions at CDF Run 2. Æ The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (py. Ano. MPI). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 3
Charged Particle Multiplicity No MPI! Tune A! Tune S 320! Æ Data at 1. 96 Te. V on the charged particle multiplicity (p. T > 0. 4 Ge. V/c, |h| < 1) for “min-bias” collisions at CDF Run 2. Æ The data are compared with PYTHIA Tune A and Tune A without multiple parton interactions (py. Ano. MPI). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 4
The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering Hard parton-parton collisions is hard (p. T > ≈2 Ge. V/c) The “underlying-event” (UE)! “Semi-hard” parton collision (p. T < ≈2 Ge. V/c) + Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”. CMS-QCD Group Meeting November 10, 2009 + Rick Field – Florida/CDF/CMS +… Multiple-parton interactions (MPI)! 5
The Inelastic Non-Diffractive Cross-Section Occasionally one of the parton-parton collisions is hard (p. T > ≈2 Ge. V/c) Majority of “minbias” events! “Semi-hard” parton collision (p. T < ≈2 Ge. V/c) + +… CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS Multiple-parton interactions (MPI)! 6
The “Underlying Event” Select inelastic non-diffractive events that contain a hard scattering Hard parton-parton collisions is hard (p. T > ≈2 Ge. V/c) The “underlying-event” (UE)! “Semi-hard” parton collision (p. T < ≈2 Ge. V/c) + Given that you have one hard scattering it is more probable to have MPI! Hence, the UE has more activity than “min-bias”. CMS-QCD Group Meeting November 10, 2009 + Rick Field – Florida/CDF/CMS +… Multiple-parton interactions (MPI)! 7
Charged Particle Multiplicity No MPI! The charged multiplicity distribution does not change between 1. 96 and 2. 2 Te. V and proton-proton is the same as Tune A prediction at proton-antiproton! 900 Ge. V! Tune A prediction at 2. 2 Te. V! Æ Data at 1. 96 Te. V on the charged particle multiplicity (p. T > 0. 4 Ge. V/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 (py. Ano. MPI). Æ Prediction from PYTHIA Tune A for proton-proton collisions at 900 Ge. V and 2. 2 Te. V. CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 8
LHC Predictions: 900 Ge. V Æ Charged multiplicity distributions for proton-proton collisions at 900 Ge. V (|h| < 2) from PYTHIA Tune A, Tune DW, Tune S 320, and Tune P 329. CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 9
“Transverse” Charged Density PTmax > 5 Ge. V/c! Æ Shows the charged particle density in the “transverse” region for charged particles (p. T > 0. 5 Ge. V/c, |h| < 2) at 900 Ge. V as defined by PTmax from PYTHIA Tune DW and Tune S 320 at the particle level (i. e. generator level). Æ Shows the charged particle multiplicity distribution in the “transverse” region (p. T > 0. 5 Ge. V/c, |h| < 2) at 900 Ge. V as defined by PTmax from PYTHIA Tune DW and Tune S 320 at the particle level (i. e. generator level). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 10
Charged Particle Multiplicity The “underlying event” is twice as active as an average HC collision! Nchg. Den = 0. 21 Æ Shows the charged particle multiplicity distribution in the “transverse” region (p. T > 0. 5 Ge. V/c, |h| < 2) at 900 Ge. V as defined by PTmax from PYTHIA Tune DW and Tune S 320 at the particle level (i. e. generator level). Æ Shows the charged particle multiplicity distribution in HC collisions (p. T > 0. 5 Ge. V/c, |h| < 2) at 900 Ge. V PYTHIA Tune A, Tune DW, Tune S 320, and Tune P 329 at the particle level (i. e. generator level). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 11
s. HC: PTmax > 5 Ge. V/c Still lots of events! Log scale! Linear scale! stot = s. EL + s. SD + s. DD + s. HC In 1, 000 HC collisions at 900 Ge. V you get 940 with PTmax > 5 Ge. V/c! Æ The inelastic non-diffractive PTmax > 5 Ge. V/c cross section (|h| < 1) versus center-of-mass energy from PYTHIA (× 1. 2). Æs. HC(PTmax > 5 Ge. V/c) varies more rapidly. Factor of 2. 3 increase between 7 Te. V (≈ 0. 56 mb) and 14 te. V (≈ 1. 3 mb). Linear on a linear scale! CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 12
PTmax Cross-Section 900 Ge. V Very important to do BOTH “soft” and “hard” physics! If we get 3, 400, 000 HC collisions at 900 Ge. V we could do both “min-bias” AND the “underlying event” In 1, 000 HC collisions at 900 Ge. V you get ~3, 000 with them! stot = s. ELand + compare s. SD PTmax+ > 5 s Ge. V/c! DD + s. HC Æ The inelastic non-diffractive PTmax > 5 Ge. V/c cross section (|h| < 2) at 900 Ge. V from PYTHIA Tune DW and Tune S 320. 10, 000 HC events. Ge. V with from Æ Number of events with PTmax > PT 0 (|h| < 2) for 1, 000 Need HCabout collisions at 900 PTmax > 5 Ge. V/c to do a nice analysis! PYTHIA Tune DW and Tune S 320. CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 13
Min-Bias “Associated” Charged Particle Density LHC 14 LHC 7 LHC 10 Tevatron 900 Ge. V RHIC 0. 2 Te. V → 1. 96 Te. V (UE increase ~2. 7 times) Tevatron 1. 96 Te. V → 14 Te. V (UE increase ~1. 9 times) LHC Æ Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (p. T > 0. 5 Ge. V/c, |h| < 1, not including PTmax) for “min-bias” events at 0. 2 Te. V, 0. 9 Te. V, 1. 96 Te. V, 7 Te. V, 10 Te. V, 14 Te. V predicted by PYTHIA Tune DW at the particle Linear scale! level (i. e. generator level). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 14
Min-Bias “Associated” Charged Particle Density LHC 14 LHC 10 LHC 7 Tevatron 900 Ge. V RHIC LHC 7 7 Te. V → 14 Te. V (UE increase ~20%) LHC 14 Linear on a log plot! Æ Shows the “associated” charged particle density in the “transverse” region as a function of PTmax for charged particles (p. T > 0. 5 Ge. V/c, |h| < 1, not including PTmax) for “min-bias” events at 0. 2 Te. V, 0. 9 Te. V, 1. 96 Te. V, 7 Te. V, 10 Te. V, 14 Te. V predicted by PYTHIA Tune DW at the particle Log scale! level (i. e. generator level). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 15
“Transverse” Charge Density factor of 2! LHC 900 Ge. V → 7 Te. V (UE increase ~ factor of 2. 1) LHC 7 Te. V Æ Shows the charged particle density in the “transverse” region for charged particles (p. T > 0. 5 Ge. V/c, |h| < 2) at 900 Ge. V as defined by PTmax from PYTHIA Tune DW and Tune S 320 at the particle level (i. e. generator level). CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 16
Important 900 Ge. V Measurements Æ The amount of activity in “min-bias” collisions (multiplicity distribution, p. T distribution, PTsum distribution, d. Nchg/dh). It is very important to measure BOTH “min-bias” and the “underlying event” at 900 Ge. V! To do this we need to collect Æ The amount of activity in the “underlying event” in hard scattering events (“transverse” Nchg distribution, “transverse” p distribution, about 5, 000 CMS “transverse” PTsum distribution for events with PTmax > 5 Ge. V/c). min-bias triggers! For every 1, 000 events here We get 3 events here! T Æ We should map out the energy dependence of the “underlying event” in a hard scattering process from 900 Ge. V to 14 Te. V! CMS-QCD Group Meeting November 10, 2009 Rick Field – Florida/CDF/CMS 17
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