Predicting “Min Predicting “Min-Bias” and the Bias” and the “Underlying Event” at the LHC “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. Outgoing Parton PT(hard) Extrapolations to RHIC. CDF Run 2 Initial-State Radiation Proton Proton � Predicting MB from the activity in the UE. Underlying Event Underlying Event Relationship between MB and the UE. Final-State � How precise is precise? Radiation Outgoing Parton � Associated Density ∆φ ∆φ ∆φ ∆φ plots. � QCD Monte-Carlo Models - Overall UE&MB@CMS UE&MB@CMS CMS at the LHC Goal. Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 1 CERN - March 2, 2010
Proton Proton-Proton Collisions Proton Collisions Elastic Scattering Single Diffraction Double Diffraction M 2 M M 1 σ σ σ tot = σ σ σ EL + σ σ σ + σ SD + + σ + σ + + +σ σ σ σ DD + + +σ + σ σ HC σ ND “Inelastic Non-Diffractive Component” Hard Core The “hard core” component contains both “hard” and “soft” collisions. “Hard” Hard Core (hard scattering) Outgoing Parton “Soft” Hard Core (no hard scattering) PT(hard) Proton Proton Proton Proton Underlying Event Underlying Event Initial-State Radiation Final-State Radiation Outgoing Parton Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 2 CERN - March 2, 2010
Inelastic Non Inelastic Non-Diffractive Cross Diffractive Cross-Section Section Inelastic Non-Diffractive Cross-Section: σ σ σ σ HC Inelastic Non-Diffractive Cross-Section: σ σ HC σ σ 70 70 RDF Preliminary RDF Preliminary 60 60 py Tune DW generator level py Tune DW generator level Cross-Section (mb) Cross-Section (mb) 50 50 40 40 My guess! 30 30 20 20 10 10 K-Factor = 1.2 K-Factor = 1.2 0 0 0 2 4 6 8 10 12 14 0.1 1.0 10.0 100.0 Center-of-Mass Energy (TeV) Center-of-Mass Energy (TeV) Linear scale! Log scale! σ tot = σ σ σ σ σ σ σ EL + σ + σ + σ + σ SD + +σ + + σ σ DD + σ + + +σ σ ND σ σ � The inelastic non-diffractive cross section versus center-of-mass energy from PYTHIA ( × 1.2). � σ σ σ HC varies slowly. Only a 13% increase between 7 TeV ( ≈ 58 mb) and 14 teV ( ≈ 66 mb). Linear σ on a log scale! Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 3 CERN - March 2, 2010
QCD Monte QCD Monte-Carlo Models: Carlo Models: High Transverse Momentum Jets High Transverse Momentum Jets Hard Scattering Outgoing Parton Initial-State Radiation PT(hard) Hard Scattering Outgoing Parton “Jet” “Hard Scattering” Component Initial-State Radiation “Jet” PT(hard) Proton Proton Final-State Radiation Outgoing Parton Underlying Event Underlying Event Proton Proton “Jet” Final-State Radiation Underlying Event Outgoing Parton Underlying Event “Underlying Event” � 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). � 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 � Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event” background to most collider observables observables receive contributions from initial and final-state radiation. and having good understand of it leads to more precise collider measurements! Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 4 CERN - March 2, 2010
CDF Run 1: Evolution of Charged Jets CDF Run 1: Evolution of Charged Jets “Underlying Event” “Underlying Event” Charged Particle ∆φ ∆φ ∆φ ∆φ Correlations Look at the charged Charged Jet #1 particle density in the P T > 0.5 GeV/c | η η | < 1 η η Direction “transverse” region! “Transverse” region 2 π π π π very sensitive to the CDF Run 1 Analysis Away Region “underlying event”! “Toward-Side” Jet Charged Jet #1 ∆φ ∆φ ∆φ ∆φ Transverse Direction Region ∆φ ∆φ ∆φ ∆φ “Toward” φ φ φ φ Leading “Toward” Jet “Transverse” “Transverse” Toward Region “Transverse” “Transverse” Transverse “Away” Region “Away” Away Region “Away-Side” Jet 0 +1 -1 η η η η � Look at charged particle correlations in the azimuthal angle ∆φ ∆φ ∆φ relative to the leading charged ∆φ particle jet. ∆φ | < 60 o as “Toward”, 60 o < | ∆φ ∆φ | < 120 o as “Transverse”, and | ∆φ ∆φ | > 120 o as “Away”. � Define | ∆φ ∆φ ∆φ ∆φ ∆φ ∆φ ∆φ � All three regions have the same size in η η - φ φ space, ∆η ∆η x ∆φ ∆φ = 2x120 o = 4 π π /3. η η φ φ ∆η ∆η ∆φ ∆φ π π Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 5 CERN - March 2, 2010
PYTHIA 6.206 Defaults PYTHIA 6.206 Defaults MPI constant probability scattering PYTHIA default parameters "Transverse" Charged Particle Density: dN/d η η η d φ η φ φ φ 1.00 Parameter 6.115 6.125 6.158 6.206 CDF Data Pythia 6.206 (default) "Transverse" Charged Density MSTP(82)=1 data uncorrected theory corrected PARP(81) = 1.9 GeV/c 0.75 MSTP(81) 1 1 1 1 MSTP(82) 1 1 1 1 0.50 PARP(81) 1.4 1.9 1.9 1.9 0.25 PARP(82) 1.55 2.1 2.1 1.9 1.8 TeV | η η η η |<1.0 PT>0.5 GeV PARP(89) 1,000 1,000 1,000 0.00 0 5 10 15 20 25 30 35 40 45 50 PARP(90) 0.16 0.16 0.16 PT(charged jet#1) (GeV/c) PARP(67) 4.0 4.0 1.0 1.0 CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20 � Plot shows the “Transverse” charged particle density versus P T (chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (P T (hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L. Default parameters give Note Change very poor description of PARP(67) = 4.0 (< 6.138) the “underlying event”! PARP(67) = 1.0 (> 6.138) Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 6 CERN - March 2, 2010
Tuning PYTHIA: Tuning PYTHIA: Multiple Parton Interaction Parameters Multiple Parton Interaction Parameters Parameter Default Description PARP(83) 0.5 Double-Gaussian: Fraction of total hadronic matter within PARP(84) PARP(84) 0.2 Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the Multiple Parton Interaction total hadronic matter. Color String Determines the energy PARP(85) 0.33 Probability that the MPI produces two gluons dependence of the MPI! Color String with color connections to the “nearest neighbors. Determine by comparing Multiple Parton Interaction PARP(86) 0.66 Probability that the MPI produces two gluons Affects the amount of with 630 GeV data! either as described by PARP(85) or as a closed initial-state radiation! gluon loop. The remaining fraction consists of Color String quark-antiquark pairs. Hard-Scattering Cut-Off PT0 PARP(89) 1 TeV Determines the reference energy E 0 . 5 PARP(82) 1.9 The cut-off P T0 that regulates the 2-to-2 PYTHIA 6.206 scattering divergence 1/PT 4 → 1/(PT 2 +P T02 ) 2 ε = 0.25 (Set A)) ε GeV/c ε ε 4 PT0 (GeV/c) Take E 0 = 1.8 TeV PARP(90) 0.16 Determines the energy dependence of the cut-off 3 ε with P T0 as follows P T0 (E cm ) = P T0 (E cm /E 0 ) ε ε ε ε = PARP(90) ε ε ε 2 ε ε ε ε = 0.16 (default) PARP(67) 1.0 A scale factor that determines the maximum 1 parton virtuality for space-like showers. The 100 1,000 10,000 100,000 CM Energy W (GeV) larger the value of PARP(67) the more initial- Reference point state radiation. at 1.8 TeV Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 7 CERN - March 2, 2010
“Transverse” Cones “Transverse” Cones vs “Transverse” Regions vs “Transverse” Regions 2 π π π π “Cone Analysis” 2 π π π π Transverse Away Region (Tano, Kovacs, Huston, Bhatti) Cone: π π (0.7) 2 =0.49 π π π π π π 6 P T90 (GeV/c) Transverse CDF PRELIMINARY MAX Data Cone 1 Region MAX Herwig+QFL MAX Pythia6.115+QFL (tuned) 5 MIN Data φ φ φ φ φ φ φ φ Leading Leading MIN Herwig+QFL Jet Jet MIN Pythia6.115+QFL (tuned) 4 Toward Region Transverse Transverse Cone 2 Region Region: 3 2 π π /3=0.67 π π π π π π Away Region 0 0 +1 -1 2 +1 -1 η η η η η η η η � Sum the P T of charged particles in two cones of radius 0.7 at the same η η as the leading jet but with | ∆Φ η η ∆Φ | = 90 o . ∆Φ ∆Φ 1 � Plot the cone with the maximum and minimum PT sum versus the E T of the leading (calorimeter) jet. 0 50 100 150 200 250 E T of leading jet (GeV) Joint UE&MB@LHC Working Group Rick Field – Florida/CDF/CMS Page 8 CERN - March 2, 2010
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